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Quantifiable astigmatism correction: Concepts and suggestions, 1986
Quantifiable astigmatism correction: Concepts and suggestions, 1986 Lee T. Nordan, M.D. La JoHa, California
ABSTRACT Astigmatism control and •correction. is of great· concern to .refractive, cataract, and corneal surgeons. This paper presents a. systematic surgical approach to astigmatism based on my experience. Concepts to improve predictability of astigmatic keratotomy· are offered for consideration. Key Words: astigmatic keratotomy, astigmatism, cylinder, radial keratotomy, Ruiz procedure
Considerations for correcting or controlling astigmatism influence virtually all anterior segment surgical techniques. Undoubtedly, astigmatism has become the common denominator uniting cataract, refractive, and corneal specialties. The quantifiable correction of astigmatism by keratotomy is now possible and is a major surgical advance based upon the keratotomy knowledge of Sato and Fyodorov. Although current techniques are certain to be refined in the future, astigmatic keratotomy presently offers patients an excellent chance of significant improvement and may be performed on a routine clinical basis. The concepts presented in this paper are substantiated by actual cases in my clinical practice but for this paper emphasis is placed on a generalized approach to astigmatism. Since the field of refractive surgery is growing and changing so rapidly, I thought a paper that presents the current state of the art in a comprehensive fashion would be of value. The treatment of many astigmatic cases has been deferred because of a natural reluctance to treat these challenging and often difficult situations. However, high astigmats, primary or postoperative, are truly troubled by spectacles or contact lenses and are grateful for even moderate improvements. A patient's willingness to accept moderate improvement allows the surgeon's goals to be conservative even though he or she may be performing innovative and demanding surgery. Of course, realistic patient expectations is a key factor determining the success or failure of any refractive surgical procedure.
The ability to correct astigmatism quantifiably has increased dramatically in the past several years and should be documented. For some surgeons, routine surgical experience now includes astigmatic correction combined with radial keratotomy (RK), cataract extraction and intraocular lens (IOL) implantation, penetrating keratoplasty (PKP), lamellar corneal graft, myopic keratomileusis, and hyperopic keratomileusis. Some of these experiences may help others gain further insight into astigmatism control and correction and prompt them to develop even better techniques. All information stated below is based upon my clinical experience and has been used successfully by other refractive surgeons. This paper is intended to be a guide for the practicing surgeon and is often purposely anecdotal. Of course, different opinions may be expressed by other surgeons and any new ideas or constructive criticism is welcome. Credit is given to individuals who introduced various concepts and techniques to me by placing their names in parentheses throughout the text. An apology is offered in advance to anyone who has been inadvertently forgotten.
PREOPERATIVE CONSIDERATIONS Patient Selection 1. Young patients may be excellent candidates for astigmatism keratotomy. The first Ruiz procedure performed in the United States (1982) was on a 9-year-old female with a refraction of +0.25 - 1.50 x 180 = 20/30 in the right eye and - 2.00 - 5.75 x
Reprint requests to Lee T. Nordan, M.D., Scripps Memorial Hospital Medical Building, 9834 Genesee Avenue, Suite 209, La Jolla, California 92037.
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175 = 20/50 in the left eye after forceps injury and characteristic Descemet's striae as well as contact lens intolerance. Two years postoperatively she had a refraction of - 4.25 - 2.25 x 150 = 20/40 in the left eye and was wearing a to ric soft contact lens with no difficulty. 2. Be sure that a pre-presbyope or presbyope is not converted into a hyperope by removing minus cylinder and creating a more hyperopic refraction (see Patient Evaluation, 3).
Patient Evaluation 1. Routine keratometry measures the corneal meridian with the greatest refractive power (highest K reading, smallest radius of curvature) and the least refractive power (lowest K reading, largest radius of curvature). These meridians should not be referred to as the axis of the cornea since an axis pertains to the correcting cylindrical lens. Ensure that all office personnel and referring sources agree on notation or surgery in the wrong meridian may occur (Beeler). For example: a) 41 x 180° 46 x 90°
Preoperative: plano - 4.00 x 90° spherical equivalent = -2.00 D spherical component = plano SURGERY ~1
I---~f---~ 44
Astigmatic Keratotomy
t+t-+-t--+-H-t-t-I
41
b) 41 x 46 x 90°
c) 41 (iJ 180° 46 (a; 90°
Postoperative: - 1.00 sph
Some ophthalmologists and optometrists assume that the 90° axis pertains to the flatter meridian in example "b". Others assume that the 90° relates to the number closest to it, which in example "b" is 46 diopters (D). There is no right or wrong; just be consistent. Notation "c" is probably the most accurate and least confusing since the "X" can be reserved for axis measurement, as when writing a refraction. 2. All astigmatism cases should be considered in minus cylinder form to design the surgery since this allows accurate spherical component determination. Then transpose to plus cylinder form and perform the astigmatic keratotomy at the axis of the plus cylinder that corresponds to the steeper meridian. Consider the following actual case: Original refraction: OD - 5.00 OS - 6.50 1st surgery: OD/RK Postoperative: OD - 3.00
+ 6.00 x 100° + 5.25 x 85° + 5.25 x 100°
The surgeon probably considered the patient a myope since the spherical component was - 5.00 and the spherical equivalent was - 2.00. However, in minus cylinder form, the patient is + 1.00 - 6.00 x 10 and clearly an excellent Ruiz procedure candidate. Spherical myopic surgery was not the surgery of choice. 3. Astigmatic keratotomy flattens the steeper meridian and allows for steepening of the flatter meridian 508
(even if a very small amount), which induces myopia. This effect is similar to squeezing a tennis ball that has been cut in half; as you squeeze, one meridian becomes steeper as the one 90 degrees away becomes flatter. A postoperative astigmatic patient who is now spherical has a spherical equivalent that is more hyperopic than preoperatively but a spherical component that is more myopic. Example:
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The spherical component has gone from plano to - 1.00; more myopic. The spherical equivalent has gone from - 2.00 to - 1.00; more hyperopic. This increased myopic component can be used to negate preoperative hyperopia. However, the spherical equivalent, which has now become more hyperopic, may disappoint a presbyope who had fair uncorrected vision preoperatively. Example: Preoperative: 42 year old: + 1.25 - 2.00 = 20/20 VA sc = 20/50 spherical equivalent + 0.25 D Postoperative: + 1.00 sphere = 20/20 VA sc = 20/80 spherical equivalent = 1.00 D Surgery might have been inadvisable for this patient if he had expected improved uncorrected vision. 4. Corneoscope pictures may document that the peripheral cornea is abnormal (burns, scarring). The corneoscope need not be used routinely since the B & L keratometer is a quantifiable corneoscope with one ring. The corneoscope is currently a qualitative instrument, not quantitative, and does not change the surgical plan in a routine case. The visual axis may be documented by corneoscopic pictures (Ruiz) but this is also done easily by other means at surgery (see Clinical Planning, Cutting, 2). 5. Ocular landmarks such as iris nevi or scleral blood vessels may aid orientation at surgery. Preoperative Polaroid photographs or diagrams are useful.
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6. Cycloplegic refraction is not routinely used since surgery is performed for the manifest refractive error. 7. Be sure that hard contact lenses have be2n stopped long enough for stable K readings and refraction. One hour with a soft lens is usually sufficient for any transient corneal edema to resolve. Hard contact lens wearers must be checked for longer periods of time to ensure the return of original corneal topography. This usually takes one to four weeks. The three conditions that must be met are (1) regular keratometry mires, (2) achievement of best-corrected vision with glasses as achieved with contact lenses, and (3) repeatable, stable readings for conditions one and two at least one week apart. Be alert for mild keratoconus cases that will occasionally be discovered in which the patient will relate a history of not having worn glasses since age 16 because vision had always been better with hard contact lenses.
TERMINOLOGY 1. As with any new and developing surgery, contradictory and confusing terminology abounds. Since transverse incisions are the most important portion of an astigmatic keratotomy, terminology based upon the T (transverse) incision is appropriate. The following is a possible scheme for identifying various forms of astigmatic keratotomy. (Spencer Thornton, M.D., proposed the term "jump T cut".)
+ t 1
bare T cut
/-\
radial bare T cut (Thornton, Jensen)
I='\
radial 4 bare T cut (Ruiz procedure)
\ I
inverse 4 bare T cut (inverse Ruiz)
radial2bareTcut
straight 4 bare
T cut (straight Ruiz)
•
5 radial mid T cut (TL of Fyodorov)
Double bare T cut 6 mm, OZ = 9 jump T cut
staggered T cut (Berkeley)
jump staggered T cut
Single 2 jump T cuts 1 mm, OZ = 7 and 8
end T cut
I
/=\
T cuts can be identified by their location from the visual axis by noting the appropriate optical zone (OZ) diameter. Single signifies that the configuration is performed on one side of the visual axis and double signifies that it is performed on both sides of the visual axis. The length of each T cut in millimeters is stated from the radial. If the T cut does not intersect a radial, the entire length is noted. Examples of terminology using the proposed scheme for some arbitrary confIgurations are as follows:
mid T cut
-I
2 bare T cut
jump radial T cut (Mallinger)
jump end T cut (Arrowsmith)
Use of eponyms for complicated patterns saves time and energy but it may cause confusion. This specific terminology scheme is advocated for use when agreement on incision identification is not universal. J CATARACT REFRACT SURG-VOL 12, SEPTEMBER 1986
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ASTIGMATIC THEORY
45
48
1. BASIC ANATOMY
43--.
!
43.5
T cut length 2.5 mm Change vertically: 43.0-43.5 = +0.5
45
Total change = 3.5 D Residual cylinder = 5.0 - 3.5 = 1.5 D
Distance between 16 cut RK = 2.35 mm
44.5 T cut length 5 mm Corrects vertically -3.0
~nce
Chord length for 90° T cut = 8 mm
+ 1. 5
Total change = 4.5 D Residual cylinder = 0.5 D
2. Astigmatic keratotomy is expected and designed to flatten the steeper meridian of the cornea. The meridian in which the astigmatic keratotomy is performed is called the primary meridian; 90 degrees away from the primary meridian is called the secondary meridian. 3. Variance of up to 10 degrees between the actual steeper meridian and the surgical meridian is usually not clinically significant. The Ruiz procedure is less forgiving than most other T-cut procedures if "off axis" and may induce irregular astigmatism for several weeks or months. 4. An astigmatic keratotomy that flattens the steeper meridian will tend to steepen the flatter meridian. This ratio is quantifiable and more noticeable for larger amounts of preoperative cylinder. This steepening of the flatter meridian has gone unnoticed for small degrees of cylinder since surgeons have not considered true induced corneal change but rather have judged postoperative success by resultant refractive error only. 5. Ruiz' s great contribution has been to document that the ratio of flattening by the primary meridian and steepening of the secondary meridian is dependent on the length of the transverse incision of a given procedure. The longer the transverse incision the more effect on the secondary meridian. The~e is no increase in effect on the primary meridian despite changes in the transverse incision length. Changes in the primary meridian depend on OZ, incision depth, and specific astigmatic keratotomy configuration (i. e., number ofT cuts). Example: 510
Corrects horizontally
between 8 cut RK = 4.70 mm
J CATARACT
(OZ = 3.5 mm)
Notice that the vertical change is constant and the horizontal meridian has changed more because of the longer transverse incision length. The ratio of secondary/primary change may be expressed as presented in the figure below (Ruiz's concept, Nordan's experience). Remember that the total amount of astigmatism corrected equals the absolute change of the primary meridian added to that of the secondary meridian, since these meridians are changing in opposite directions. The ratio of the change within the total amount is important because the change of the secondary meridian determines the amount of myopic spherical component induced. 112
Secondary Meridian Primary Meridian
-,.._ _~118
5.0
4.0
3.0
Length of Transverse Incision (mm) Ruiz Procedure
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2.0
1.5
CHANGE
Another figure depicting the same concept shows that the ratio of change linking the primary to the secondary meridian varies as the length of the transverse incision is varied while correcting a hypothetical patient with 6 D of astigmatism. The OZ must be enlarged as the transverse length is lengthened to ensure a constant total astigmatic correction. Clinical Option 2
Clinical Option 1 Diopters of Change
6
6
6
Clinical Option 3
6
6
OZ
3.15
T ransverse Length
1.5
.. 0
3.0
•. 0
5.0
Secondari: Primary
118
116
lIS
113
112
JL
.J!L
...L
.il..
..1..
Actual Dioptric Change
5.33
3.50
5.15
5
3.75
•. 5
will be induced, which will equal 1/9 of the preoperative cylinder. Expected postoperative refraction = -1. 00 sphere. Example:
+ 2.00 - 6.00 x,90° Induced myopia of -2.00 is desired to negate the + 2.00 of hyperopia; -2.00 = 1/3 of - 6.00 cylinder; therefore, a ratio of 1/2 secondary/primary is desired. Use a 5-mm length T cut with a 3. 75-mm optical zone. A different optical zone would be necessary to correct a given amount of cylinder if the transverse incision length changed. 6. This steepening of the flatter meridian tends to negate a radial keratotomy, which is designed to flatten a steep meridian. Therefore, a compensatory factor must be added to the sphere of the refraction when RK and astigmatism are corrected together if the surgeon is aiming for emmetropia (Nordan rule). This compensatory factory is not large when dealing with small preoperative cylinder. This compensatory factor equals one half the preoperative cylinder, which means that I operate on the spherical equivalent not the spherical component when correcting a compound myopic astigmat by combined RK and astigmatic keratotomy. Since a mild undercorrection is desirable, the difference between the two approaches is not clinically significant for low degrees of astigmatism. Example:
•
This allows a surgeon to predict the amount of myopia induced because it equals the amount of steepening of the secondary meridian. This may be expressed as a percentage of the total astigmatism to be corrected.
- 2.00 - 1.50 x 180 0 Choice 1: Consider spherical component only a. RK: OZ to correct 2 D == 4.0 mm h. Jump T cut, OZ 7 mm/1.5 mm to correct 1.50 D of cylinder
Plano -9.00 x 90° Ruiz procedure T length 1.5 mm Postoperative: - 1. 00 sphere Surgeon's View
Eight diopters of change horizontally (flattening) is expected for every 1 D of change vertically (steepening). Therefore, the 9 D total of cylinder will be corrected by 9 (8/9) = 8 D horizontally and by 9 (1/9) = 1 D vertically. One diopter of myopia
Choice 2: Consider spherical component to be the spherical equivalent a, Consider as - 2,75 - 1. 50 x 180 0 (Nordan Rule) h. RK: OZ to correct - 2,75 D == 3.75 mm c, Jump cut, OZ 7 mm/ 1.5 mm to correct 1.50 D of cylinder
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But now consider the following:
7.
-2.00 - 6.00 x 180°
-----I
RK OZ = 4.0 mm to correct 2 D of myopia Ruiz OZ = 3.5 mm to correct 6 D of cylinder I predict a result of -2.00 D, undercorrected sphere
8.
9. Nordan Rule -2.00 -6.00: Considers as a -5.00 -6.00 by adding 'h of the cylinder (3) to the sphere.
RK OZ = 3.0 with redeepening of radials at 5 and 7 to correct - 5.00 D. Actually only 2 D of myopia will be corrected.
10.
Ruiz OZ = 3.5 to correct ~6.00 D of cylinder. (The transverse length of a Ruiz with RK is always 1.5 mm to induce as little myopia as possible.)
11.
In other words, you must treat for 5 D to achieve 2 D in face of the Ruiz procedure, or "it's difficult to overcorrect sphere with a strong astigmatic keratotomy in position."
12.
It is interesting that both the jump end T cut of 6 mm, OZ 8 (Arrowsmith) and the radial 4 bare T cuts, 5 mm, (Ruiz) have essentially the same effect on the secondary meridian. The larger the cylinder correction, the harder it is to correct the spherical myopia. The maximum myopic spherical correction possible in conjunction with the Ruiz procedure is 3.5 D to 4.0 D. The effect of a transverse incision is indirectly proportional to its distance from the visual axis. For a 30-year-old - 6.00 - 4.00 x 180°, some compromise is necessary. Perform either a maximum 16-cut RK for spherical correction and attempt a T-cut procedure for astigmatism correction, expecting a result of plano - 2.00 x 180°, or use a stronger T-cut procedure for astigmatism combined with an 8-cut RK and expect - 2.00 sphere. I would pick the first alternative if uncorrected vision was to be maximized and the second alternative if contact lens wear was desired. Always use a Ruiz of l.5 mm T cut for compound myopic astigmatism because it induces the least myopia. Limit the transverse length of any astigmatic incision to 5 mm because a paradoxical flattening of the secondary meridian can occur with incisions longer than this. Keratometry postoperatively is often inaccurate after astigmatic keratotomy. The keratometer measures only one point of an aspheric cornea.
Each surgeon should be able to document his or her compensatory factor after analyzing several compound myopic astigmats who have been treated by combined RK and astigmatic keratotomy. Ajump end T cut, 6 mm, OZ = 8 mm (Arrowsmith) tends to steepen the secondary meridian by about one half to the full amount of flattening of the primary meridian. This causes either a mild hyperopic shift or no change in the spherical equivalent. Again, I would operate on the spherical equivalent for the RK portion of the procedure. Example: -2.00 - 3.00 x 180 0 Consider as
~3.50 ~3.oo
sphere x 180
RK OZ = 3.25 mm to correct ~3.50 D sphere
1----
T cut to correct 3.00 D cyl
.512
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13. This aspheric cornea allows better uncorrected vision than expected when considering the patient's refraction. Also, presbyopes often experience inappropriately better reading vision along with excellent distance vision. 14. A residual myopia of - 0.75 Dafter RK will function the same as a-I. 50 D add and still allow 20/25 distance vision. Refractive astigmatism is equal to corneal astigmatism plus lenticular astigmatism (assuming normal posterior pole) in a vector sense. 15. Actual corneal change induced by an astigmatic keratotomy is equal to the postoperative corneal cylinder minus the preoperative corneal cylinder in a vector sense. Also, subtraction of the preoperative refractive astigmatism from the postoperative refractive astigmatism (in a vector sense) will establish induced corneal change.
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Vector Analysis of Astigmatic Keratotomy
c R r---------=='*------ 180°
9(}0
9(}0
L
L
135°
135°
Pre-op Plano - 4.00 x K
= 41
9(}0;
@ 80°; C 44 @ 170°
Post-op plano - 1.00 x 45°; R = -1.00
R = -4.00
= -3.00
45° (post-op) KI
Induced corneal change = KI KI = (astigmatism post-op) - (astigmatism pre-op)
90° ------------~~~---------
R = Refractive astigmatic vector L = Lenticular astigmatic vector C = Corneal astigmatic vector
16. 17. 18.
19.
Axes are labeled one half their normal amount to allow addition of vectors without compensatory mathematics (Tate). Operate on the steeper keratometric meridian to avoid irregular astigmatism. Operate on the refractive astigmatic power to minimize postoperative cylinder. This is important when large amounts oflenticular astigmatism exist. Operating on the refractive axis is clinically acceptable because it usually corresponds closely to the steeper keratometric meridian, but be alert to occasional cases with large degrees of lenticular astigmatism. Irregular astigmatism refracts more hyperopic.
20. Irregular astigmatism is often associated with poorly healed incisions and will resolve in a few weeks as the incisions heal. 21. Irregular astigmatism after astigmatic keratotomy is basically an irregularity of the stroma that is reflected in the epithelium. The air-epithelium interface is the site of action but not the cause of the defect.
~----...~-' 22. Irregular astigmatism can be caused by epithelial disease, i.e., punctate keratopathy, bullous keratopathy.
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23. Regular and irregular astigmatism may coexist. 24. Astigmatic keratotomy only treats regular astigmatism. CLINICAL PLANNING Thinking 1. Mid T cuts and jump cuts may be performed as singles -on only one side of the visual axis (Berkeley). 2. Bare T cuts and the Ruiz procedure should be performed on both sides of the visual axis. 3. If single T cuts are performed, the preferred location is under the upper lid or nasally. 4. Ruiz procedure - 3.5 OZ or greater to avoid glare and diplopia. 5. Astigmatic keratotomy should be centered about the visual axis, not the corneal center. 6. Avoid four-corner incisions; they cause increased scarring, pain, and recurrent erosion. 7. Consider treating astigmatism combined with RK at - 1.25 D with the rule, - 1.00 D against the rule. 8. Astigmatism correction is not greatly affected by age and lOP as is RK surgery.
Cutting 1. Mark visual axis accurately; a miotic pupil is valuable. 2. The proper meridian for an astigmatic procedure may be marked by a. Judgment and approximation (experienced surgeon) b. Microscope reticle (Fenzl) c. Circular marker (Mendez) Remember that the K readings, patient placement, microscope placement all have a 5 degree margin of error. 3. Use epithelial markers as indicated. 4. Use an ultrasound pachymeter to ensure consistent depth. In my opinion, 85% achieved depth of corneal thickness is optimal for transverse incisions. 5. Measure over or near PKP scars and change blade depth as necessary. Often scarred areas are thinner than the surrounding tissue. 6. A front-cutting blade should be used for long transverse incisions to allow maximum visibility. 7. A front-cutting diamond blade cuts to a depth of approximately 90% of corneal thickness. A bias of - 5% from corneal thickness is necessary to achieve an 85% depth cut. 8. It is useful to fixate the globe with a Kremer forceps at the meridian 90 degrees away from the operative meridian to ensure proper orientation. POSTOPERATIVE 1. Transverse incisions must gape to achieve significant astigmatic correction. 2. Patch with antibiotic ointment or drops until the epithelium is intact. 514
3. Do not use a T lens for seven to 10 days postoperatively because tight lens syndrome is common. 4. Lateral gape of Ruiz pseudoradial incisions is common after PKP. 5. Hyperopia caused by irregular astigmatism will resolve as the irregular astigmatism resolves.
ADDITIONAL ASTIGMATIC PEARLS 1. Astigmatism after PKP-reduce goal by 40%. If preop PKP astigmatism is + 6.0 D, aim for 3.5 D. 2. Ruiz procedure combined with cataract-adjust the IOL power for expected change in spherical equivalent. 3. Cataract after previous astigmatic keratotomy and RK-do your best routine cataract and IOL procedure but be sure to compute IOL power accurately. Two methods for IOL power calculations after astigmatic keratotomy include the following: (1) current K readings and axial length. Be aware of possible keratometry inaccuracies. (2) Compute IOL power by using original Ks and axial length. Compute the difference in refraction between preop and postop keratotomy. Add this difference to the computed IOL power. Until further advances are made, I recommend using both methods of determining IOL power after refractive surgery. Examples: Pre-keratotomy refraction: + 1.00 - 3.00 x goo K: 40x 43 @ 180° AL: 23.5 Post-keratotomy refraction: + 0.50 sphere K: 40.50 x 41 @ 180° AL: 23.5 Method 1: Using postop Ks: AL 23.5 Average K = 40.75 (40.5 + 41.(0) IOL = 21.50 D 2 Method 2: Using preop Ks and accounting for change in refraction from keratotomy procedure: AL 23.5 Postop refraction minus preop refraction spherical equivalent: + 0.50 - (-0.50) = +1.00 postop preop Original IOL power preop calculated at 23.5, K = 41.5, IOL = 20.5: 20.5 + 1.00 = 21.5 D In other words, the IOL power must compensate for the increase in hyperopia after RK or astigmatic keratotomy by becoming stronger than the original preoperative calculation would indicate. 4. Ruiz after RK-reduce goal by 40% as with PKP. 5. To determine if a patient needs an RK in conjunction with an astigmatic procedure, consider the following rule: Multiply the -cyl by 20% and algebrai-
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cally add this to the sphere value of the refraction. If the result is more myopic than - 0.50 D, then an RK based on spherical equivalent (adjusted by appropriate factors) is indicated ifthe goal is emmetropia.
CHARTS See Appendix A, B, C, D: These charts represent my philosophy of refractive surgery. CLINICAL EXAMPLES Several clinical examples are listed below with my preferred method of correction. The assumed goal is emmetropia in all cases. Of course, appropriate factors for each surgeon which pertain to the patient's age, lOP, sex must be taken into account. Preoperative Surgery 1. - 2.00 - 0.75 x 180° a) RK; no rx for cylinder 2. - 2.00 - 1.50 x 180°
7.
+ 3.00 - 6.00 x 180°
Ruiz; 3.5 mm OZ, 5 mm length at 90°
8. PKP with 8 D of astigmatism
Ruiz; plan for 5.0 D, length 2.5 mm
9. - 5.00 - 2.50 x 180°
a) RK for - 6.25 D b) double jump radial T cuts at 7.0 mm OZ, length 2.5 mm
10. RK post-op jump T cut at 7.0 mm OZ, + 0.50 - 2.00 x 180° 90° superior; reopen radials radials at 90° and 180° at 90° superior and inferior 11. RK post-op
+ 0.50 - 2.00
x 180° radials "off axis"
double radial bare T cut (Thorn ton, Jensen) and reopen adjacent radials
b) RK for -2.37 D
12. RK post-op + 1.00 - 5.00 x 180°
Ruiz; 2.5 mm, plan for 3.0 D
a) RK for -2.75 D b) single jump radial Tcut at 7 mm OZ; length 1.5 mm at 90° c) any of the T cuts will function well d) consider double bare T cut 7.0 mm OZ, 2.5 mm; rotate accordingly (Thornton, Jensen)
13. - 6.00 - 5.00 x 180°
Myopic keratomileusis and Ruiz procedure at 90°
3. - 2.00 - 3.00 x 180°
a) RK for - 3.50 b) double jump radial T cut, 7.0 mm OZ or double jump T cut, 7.0 mm OZ or double jump end T cut, 9.0 mm OZ, 6 mm length or double jump staggered T cut, 7.00 mm OZ, length 2.0 mm
4. - 2.00 - 5.00 x 180°
a) 6 cut RK for - 4.50 b) double straight 4 bare T cut, 1.5 mm length (straight Ruiz) at 90°
5. + 1.50 - 2.00 x 180°
a) 20-year-old; single jump radial Tcut at 7.0 mm OZ, length 2.00 mm at 90° b) 50-year-old; no surgery; presbyope and spherical equivalent will become more hyperopic with astigmatism correction
6. + 1.00 - 6.00 x 180°
Ruiz; 3.5 mm OZ, 2.5 mm length at 90°
14.
+ 2.00 - 4.00 x 180°
Ruiz; 5.0 mm length
15. Cataract 460.) 90° 43 @ 180°
manipulate wound by allowing recession at 90° to correct astigmatism
16. Cataract 46 @ 90° 40 0) 180°
double bare T cut at 7.0 mm OZ, 3.5 mm length, axis 90°; manipulate phaco wound as necessary under keratometric control to achieve appropriate postop corneal shape
17. Cataract 90° 40 46 @ 180°
double bare T cut at 7.0 mm OZ, 3.5 mm length, axis 180°; manipulate phaco wound as necessary under keratometric control to achieve appropriate pas top corneal shape
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CATARACT/IOL ASTIGMATISM CONSIDERATIONS Cataract surgery has been advanced immeasurably by the introduction of the IOL, especially the posterior chamber IOL. However, excellent results require that significant astigmatism be corrected or that minimal astigmatism be maintained. Intraocular lens surgery benefits from refractive surgery techniques. Astigmatic keratotomy and wound manipulation may be used at the time of surgery to minimize postoperative astigmatism (Martin, Maloney). Recession (loose suturing) of a cataract wound is more stable than a resection (tight suturing). The concept of always operating on the steep meridian and performing a wound recession is an excellent one, but many surgeons find operating from the side tedious (Terry). It is hoped that astigmatic keratotomy can allow surgery from above in all cases and provide enough astigmatic control so wound manipulation need not be pursued beyond its appropriate limits.
1.25 - 1.75 D
Double bare T cut with peripheral radial; OZ=7; length ofT cut= 3.5 mm 2.0 - 2.5 D
In cataract/IOL surgery, the approach to wound management is based on preoperative keratometry. The options available to the surgeon to correct astigmatism usually include the following possibilities: 1. Wound superiorly-tighten, neutral, loosen 2. Wound rotated temporally-loosen 3. Wound enlarged from normal choice (i. e., 3 to 6 mm; 6 to 12 mm) to gain increased astigmatic control 4. Wound plus astigmatic keratotomy
Double 2 bare T cut with step-ladder radial; OZ=7.9; length of Tcut= 3.5 mm
I believe that long-term correction of significant against-the-rule astigmatism (flatter meridian vertical) is not achieved by using tight sutures with a wound position along the flatter meridian. A loose wound (recession), on the other hand, allows the steeper meridian to flatten and does lead to more effective longterm astigmatism correction. The larger the wound, the larger the astigmatism correction possible up to the limit of maintaining a watertight wound. I assume the following approximate relationshps:
WOUND LENGTH
3 mm 6 mm 10-12 mm
MAXIMUM ASTIGMATIC CORRECTION BY LOOSENING
o diopters 2.5 diopters 4.5 diopters
The total amount of astigmatism correction obtained is determined by the wound's effect plus that of the keratotomy. I currently use three keratotomy patterns with cataract surgery and have assigned them a dioptric astigmatism correction value as follows: 516
4.0 - 5.0 D
Ruiz; OZ=4.25 mm; length of transverse=3.5 mm
Qualitative or quantitative keratometry during cataract surgery is possible after astigmatic keratotomy since the OZ is 7.0 mm. The relative relationship between the primary and secondary meridia is important, not the absolute number of the quantitative keratometer since the aspheric shape of the cornea may make this number inaccurate.
J CATARACT REFRACT SURG-VOL
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Preoperatively the surgeon may plan for total astigmatism correction by considering the amount of astigmatism to be gained by a recession of the wound and then adding the specific astigmatic keratotomy necessary. During surgery the astigmatic keratotomy is performed before the anterior chamber is entered. The surgeon should maintain a conservative attitude and aim for a combined effect of perhaps one diopter less than the total preoperative astigmatic error. This allows an astigmatic keratotomy of the lowest value (and least number of incisions) to be used. The surgeon must be very confident of the predictability of his or her normal wound closure technique to allow for the anticipated cylinder changes
associated with this wound closure combined with the astigmatic keratotomy. Recently I have been using a simple intraoperative tonometer based on the Barraquer tonometer design, which ensures similar lOP during all keratometry measurements (Kratz). CONCLUSION Astigmatism is a problem that can effectively be approached by astigmatic keratotomy. Certainly, astigmatic keratotomy sophistication will improve in the future but currently it appears to be safe and quantifiable enough to establish it as a routine part of our surgical armamentarium. Many difficult astigmatic cases can now be tackled by concerned eye surgeons to benefit these deserving patients.
APPENDIX A
RUIZ TECHNIQUE - CORRECTION OF ASTIGMATISM DJOPTERS OF ASTIGMATISM
LENGTH OF STEP LADDER INCISIONS
(SMALL) 2.Smm
(LARGE) Smm
2
3
4
5
6
7
8
5.25 (-0.3)
4.75 (-0.5)
4.25 (-0.7)
3.75 (-0.9)
3.50 ( -1.0)
3.25 (-1.2)
3.00 (-1.3)
5.50 (-0.5)
5.00 (-0.8)
4.50 (-1.00)
4.00 (-1.3)
3.75 (-1.5)
3.50 (-1.8)
3.25 (-2.00)
INSTRUCTIONS REMEMBER: 1. 2. 3. 4. 5. 6. 7. 8. 9.
Refraction in negative cylinder format. Find column for diopters of astigmatism correction desired. Choose either middle or lower box of column depending upon amount of induced myopia desired (number in parentheses). The number above the parentheses is the proper optical zone. The box to the extreme left of the chosen row is the length of thestep-Iadder incision. Surgeon's own factor for patient age, etc., must be taken into account. If spherical component less than or equal to 0, then use 1.5 mm step-ladder incisions. Combine with radial keratotomy if desired. Adjust your technique according to your experience. This chart assumes incision depth of 80% depth for all incisions.
J CATARACT REFRACT SURG-VOL
RUIZ TECHNIQUE PERFORMED AT STEEPER MERIDIAN EQUALS AXIS OF PLUS CYLINDER REFRACTION OR 90° AWAY FROM NEGATIVE CYLINDER REFRACTION. FEET
90"
leo~3~S:800
.s:zrs?35
0
90°
HEAD RUIZ AT 90"
12, SEPTEMBER 1986
SURGEON'S VIEW
AUIZ AT 180 0
517
APPENDIX B
T-CUTS FOR ASTIGMATIC CORRECTION 1.75-2.25
1.0-1.50
DIOPTERS
OIOPTERS
GUIDELINES
1. No incisions intersect 2.
Place T-cuts above 180° meridian on cornea when possible.
3. Place staggered T-cuts al 7 mm oplical zone.
3.25-3.50
2.50-3.0
OIOPTERS
DIOPTERS
4. Change according 10 your experience.
5. Perform T -cuts in steeper meridian = axis of positive cylinder refraction or 90° away from axis of negalive cylinder refraction
SURGEON'S VIEW
APPENDIX D
APPENDIX C
COMBINED RADIAL KERATOTOMY
REFRACTIVE SURGERY SELECTION GUIDE
and
RUIZ TECHNIQUE
1985
-sph
GUIDELINES
-cyl
(original reiraction)
-cyl
'new' refraction for optical zone considerations
+
1. Refraction in negative cylinder format.
2. Find sphere on vertical scale. 3. Proceed horizontally to right until cylinder power reached.
H Y P E R 0
P I
A
4.
This location determines choiclI of surgery.
5.
Adjust chart to your preferences and experience.
7.0
0
P I
A
3.0 4.0 5.0 6.0 7.0 0 9. 0 10. 0 11.0
518
HKM+ RUIZ
HKM
6.0 5.0 4.0 3.0 2.0 1.0 0 1.0 2.0
M Y
-sph + 1_
9.0 8.0
RUIZ 1.5mml
H·EPI
RUIZ (4.5mm)
RK + RUIZ
RK
@ /1'
RK
+
@ /1.'-
MKM
T·CUT
8.0 8.5 7.0 7.5
~
r-----: _____ J
I
450
400
INSTRUCTIONS
--'-----j
C-----------;UIZ (2.5 mm) 0.5 10 1.5 2.0 2.5 3.0 3.5 \ 4.0 4.5 5.0 5.5
.00
C;II
cyl
J
1.
2. 3.
4. 5. 6.
Refraction in negative cylinder format. Use RUIZ with 1.5 mm tangential incisions. Choose optical zone for Ruiz.
Choose optical zone for 6 Incision RK based on 'new' sphere. Maximum limit of spherical correction equals 3.5 D. Change technique according to your experience.
375
325
300
REMEMBER:
RUIZ TECHNIQUE PERFORMED AT STEEPER MERIDIAN EQUALS AXIS OF PLUS CYLINDER REFRACTION OR (90·)AWAY FROM AXIS OF
MINUS CYLINDER REFRACTION.
~EET
"'.
,JSJ2:\':". .~350
MK+RUIZ
",'
MY·EPI
J CATARACT REFRACT
SURG-VOL 12, SEPTEMBER 1986
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ABSTRACT Astigmatism control and •correction. is of great· concern to .refractive, cataract, and corneal surgeons. This paper presents a. systematic surgical approach to astigmatism based on my experience. Concepts to improve predictability of astigmatic keratotomy· are offered for consideration. Key Words: astigmatic keratotomy, astigmatism, cylinder, radial keratotomy, Ruiz procedure
Considerations for correcting or controlling astigmatism influence virtually all anterior segment surgical techniques. Undoubtedly, astigmatism has become the common denominator uniting cataract, refractive, and corneal specialties. The quantifiable correction of astigmatism by keratotomy is now possible and is a major surgical advance based upon the keratotomy knowledge of Sato and Fyodorov. Although current techniques are certain to be refined in the future, astigmatic keratotomy presently offers patients an excellent chance of significant improvement and may be performed on a routine clinical basis. The concepts presented in this paper are substantiated by actual cases in my clinical practice but for this paper emphasis is placed on a generalized approach to astigmatism. Since the field of refractive surgery is growing and changing so rapidly, I thought a paper that presents the current state of the art in a comprehensive fashion would be of value. The treatment of many astigmatic cases has been deferred because of a natural reluctance to treat these challenging and often difficult situations. However, high astigmats, primary or postoperative, are truly troubled by spectacles or contact lenses and are grateful for even moderate improvements. A patient's willingness to accept moderate improvement allows the surgeon's goals to be conservative even though he or she may be performing innovative and demanding surgery. Of course, realistic patient expectations is a key factor determining the success or failure of any refractive surgical procedure.
The ability to correct astigmatism quantifiably has increased dramatically in the past several years and should be documented. For some surgeons, routine surgical experience now includes astigmatic correction combined with radial keratotomy (RK), cataract extraction and intraocular lens (IOL) implantation, penetrating keratoplasty (PKP), lamellar corneal graft, myopic keratomileusis, and hyperopic keratomileusis. Some of these experiences may help others gain further insight into astigmatism control and correction and prompt them to develop even better techniques. All information stated below is based upon my clinical experience and has been used successfully by other refractive surgeons. This paper is intended to be a guide for the practicing surgeon and is often purposely anecdotal. Of course, different opinions may be expressed by other surgeons and any new ideas or constructive criticism is welcome. Credit is given to individuals who introduced various concepts and techniques to me by placing their names in parentheses throughout the text. An apology is offered in advance to anyone who has been inadvertently forgotten.
PREOPERATIVE CONSIDERATIONS Patient Selection 1. Young patients may be excellent candidates for astigmatism keratotomy. The first Ruiz procedure performed in the United States (1982) was on a 9-year-old female with a refraction of +0.25 - 1.50 x 180 = 20/30 in the right eye and - 2.00 - 5.75 x
Reprint requests to Lee T. Nordan, M.D., Scripps Memorial Hospital Medical Building, 9834 Genesee Avenue, Suite 209, La Jolla, California 92037.
J CATARACT REFRACT SURG-VOL
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175 = 20/50 in the left eye after forceps injury and characteristic Descemet's striae as well as contact lens intolerance. Two years postoperatively she had a refraction of - 4.25 - 2.25 x 150 = 20/40 in the left eye and was wearing a to ric soft contact lens with no difficulty. 2. Be sure that a pre-presbyope or presbyope is not converted into a hyperope by removing minus cylinder and creating a more hyperopic refraction (see Patient Evaluation, 3).
Patient Evaluation 1. Routine keratometry measures the corneal meridian with the greatest refractive power (highest K reading, smallest radius of curvature) and the least refractive power (lowest K reading, largest radius of curvature). These meridians should not be referred to as the axis of the cornea since an axis pertains to the correcting cylindrical lens. Ensure that all office personnel and referring sources agree on notation or surgery in the wrong meridian may occur (Beeler). For example: a) 41 x 180° 46 x 90°
Preoperative: plano - 4.00 x 90° spherical equivalent = -2.00 D spherical component = plano SURGERY ~1
I---~f---~ 44
Astigmatic Keratotomy
t+t-+-t--+-H-t-t-I
41
b) 41 x 46 x 90°
c) 41 (iJ 180° 46 (a; 90°
Postoperative: - 1.00 sph
Some ophthalmologists and optometrists assume that the 90° axis pertains to the flatter meridian in example "b". Others assume that the 90° relates to the number closest to it, which in example "b" is 46 diopters (D). There is no right or wrong; just be consistent. Notation "c" is probably the most accurate and least confusing since the "X" can be reserved for axis measurement, as when writing a refraction. 2. All astigmatism cases should be considered in minus cylinder form to design the surgery since this allows accurate spherical component determination. Then transpose to plus cylinder form and perform the astigmatic keratotomy at the axis of the plus cylinder that corresponds to the steeper meridian. Consider the following actual case: Original refraction: OD - 5.00 OS - 6.50 1st surgery: OD/RK Postoperative: OD - 3.00
+ 6.00 x 100° + 5.25 x 85° + 5.25 x 100°
The surgeon probably considered the patient a myope since the spherical component was - 5.00 and the spherical equivalent was - 2.00. However, in minus cylinder form, the patient is + 1.00 - 6.00 x 10 and clearly an excellent Ruiz procedure candidate. Spherical myopic surgery was not the surgery of choice. 3. Astigmatic keratotomy flattens the steeper meridian and allows for steepening of the flatter meridian 508
(even if a very small amount), which induces myopia. This effect is similar to squeezing a tennis ball that has been cut in half; as you squeeze, one meridian becomes steeper as the one 90 degrees away becomes flatter. A postoperative astigmatic patient who is now spherical has a spherical equivalent that is more hyperopic than preoperatively but a spherical component that is more myopic. Example:
J CATARACT REFRACT
The spherical component has gone from plano to - 1.00; more myopic. The spherical equivalent has gone from - 2.00 to - 1.00; more hyperopic. This increased myopic component can be used to negate preoperative hyperopia. However, the spherical equivalent, which has now become more hyperopic, may disappoint a presbyope who had fair uncorrected vision preoperatively. Example: Preoperative: 42 year old: + 1.25 - 2.00 = 20/20 VA sc = 20/50 spherical equivalent + 0.25 D Postoperative: + 1.00 sphere = 20/20 VA sc = 20/80 spherical equivalent = 1.00 D Surgery might have been inadvisable for this patient if he had expected improved uncorrected vision. 4. Corneoscope pictures may document that the peripheral cornea is abnormal (burns, scarring). The corneoscope need not be used routinely since the B & L keratometer is a quantifiable corneoscope with one ring. The corneoscope is currently a qualitative instrument, not quantitative, and does not change the surgical plan in a routine case. The visual axis may be documented by corneoscopic pictures (Ruiz) but this is also done easily by other means at surgery (see Clinical Planning, Cutting, 2). 5. Ocular landmarks such as iris nevi or scleral blood vessels may aid orientation at surgery. Preoperative Polaroid photographs or diagrams are useful.
SURG-VOL 12, SEPTEMBER 1986
6. Cycloplegic refraction is not routinely used since surgery is performed for the manifest refractive error. 7. Be sure that hard contact lenses have be2n stopped long enough for stable K readings and refraction. One hour with a soft lens is usually sufficient for any transient corneal edema to resolve. Hard contact lens wearers must be checked for longer periods of time to ensure the return of original corneal topography. This usually takes one to four weeks. The three conditions that must be met are (1) regular keratometry mires, (2) achievement of best-corrected vision with glasses as achieved with contact lenses, and (3) repeatable, stable readings for conditions one and two at least one week apart. Be alert for mild keratoconus cases that will occasionally be discovered in which the patient will relate a history of not having worn glasses since age 16 because vision had always been better with hard contact lenses.
TERMINOLOGY 1. As with any new and developing surgery, contradictory and confusing terminology abounds. Since transverse incisions are the most important portion of an astigmatic keratotomy, terminology based upon the T (transverse) incision is appropriate. The following is a possible scheme for identifying various forms of astigmatic keratotomy. (Spencer Thornton, M.D., proposed the term "jump T cut".)
+ t 1
bare T cut
/-\
radial bare T cut (Thornton, Jensen)
I='\
radial 4 bare T cut (Ruiz procedure)
\ I
inverse 4 bare T cut (inverse Ruiz)
radial2bareTcut
straight 4 bare
T cut (straight Ruiz)
•
5 radial mid T cut (TL of Fyodorov)
Double bare T cut 6 mm, OZ = 9 jump T cut
staggered T cut (Berkeley)
jump staggered T cut
Single 2 jump T cuts 1 mm, OZ = 7 and 8
end T cut
I
/=\
T cuts can be identified by their location from the visual axis by noting the appropriate optical zone (OZ) diameter. Single signifies that the configuration is performed on one side of the visual axis and double signifies that it is performed on both sides of the visual axis. The length of each T cut in millimeters is stated from the radial. If the T cut does not intersect a radial, the entire length is noted. Examples of terminology using the proposed scheme for some arbitrary confIgurations are as follows:
mid T cut
-I
2 bare T cut
jump radial T cut (Mallinger)
jump end T cut (Arrowsmith)
Use of eponyms for complicated patterns saves time and energy but it may cause confusion. This specific terminology scheme is advocated for use when agreement on incision identification is not universal. J CATARACT REFRACT SURG-VOL 12, SEPTEMBER 1986
509
ASTIGMATIC THEORY
45
48
1. BASIC ANATOMY
43--.
!
43.5
T cut length 2.5 mm Change vertically: 43.0-43.5 = +0.5
45
Total change = 3.5 D Residual cylinder = 5.0 - 3.5 = 1.5 D
Distance between 16 cut RK = 2.35 mm
44.5 T cut length 5 mm Corrects vertically -3.0
~nce
Chord length for 90° T cut = 8 mm
+ 1. 5
Total change = 4.5 D Residual cylinder = 0.5 D
2. Astigmatic keratotomy is expected and designed to flatten the steeper meridian of the cornea. The meridian in which the astigmatic keratotomy is performed is called the primary meridian; 90 degrees away from the primary meridian is called the secondary meridian. 3. Variance of up to 10 degrees between the actual steeper meridian and the surgical meridian is usually not clinically significant. The Ruiz procedure is less forgiving than most other T-cut procedures if "off axis" and may induce irregular astigmatism for several weeks or months. 4. An astigmatic keratotomy that flattens the steeper meridian will tend to steepen the flatter meridian. This ratio is quantifiable and more noticeable for larger amounts of preoperative cylinder. This steepening of the flatter meridian has gone unnoticed for small degrees of cylinder since surgeons have not considered true induced corneal change but rather have judged postoperative success by resultant refractive error only. 5. Ruiz' s great contribution has been to document that the ratio of flattening by the primary meridian and steepening of the secondary meridian is dependent on the length of the transverse incision of a given procedure. The longer the transverse incision the more effect on the secondary meridian. The~e is no increase in effect on the primary meridian despite changes in the transverse incision length. Changes in the primary meridian depend on OZ, incision depth, and specific astigmatic keratotomy configuration (i. e., number ofT cuts). Example: 510
Corrects horizontally
between 8 cut RK = 4.70 mm
J CATARACT
(OZ = 3.5 mm)
Notice that the vertical change is constant and the horizontal meridian has changed more because of the longer transverse incision length. The ratio of secondary/primary change may be expressed as presented in the figure below (Ruiz's concept, Nordan's experience). Remember that the total amount of astigmatism corrected equals the absolute change of the primary meridian added to that of the secondary meridian, since these meridians are changing in opposite directions. The ratio of the change within the total amount is important because the change of the secondary meridian determines the amount of myopic spherical component induced. 112
Secondary Meridian Primary Meridian
-,.._ _~118
5.0
4.0
3.0
Length of Transverse Incision (mm) Ruiz Procedure
REFRACT SURG-VOL 12, SEPTEMBER 1986
2.0
1.5
CHANGE
Another figure depicting the same concept shows that the ratio of change linking the primary to the secondary meridian varies as the length of the transverse incision is varied while correcting a hypothetical patient with 6 D of astigmatism. The OZ must be enlarged as the transverse length is lengthened to ensure a constant total astigmatic correction. Clinical Option 2
Clinical Option 1 Diopters of Change
6
6
6
Clinical Option 3
6
6
OZ
3.15
T ransverse Length
1.5
.. 0
3.0
•. 0
5.0
Secondari: Primary
118
116
lIS
113
112
JL
.J!L
...L
.il..
..1..
Actual Dioptric Change
5.33
3.50
5.15
5
3.75
•. 5
will be induced, which will equal 1/9 of the preoperative cylinder. Expected postoperative refraction = -1. 00 sphere. Example:
+ 2.00 - 6.00 x,90° Induced myopia of -2.00 is desired to negate the + 2.00 of hyperopia; -2.00 = 1/3 of - 6.00 cylinder; therefore, a ratio of 1/2 secondary/primary is desired. Use a 5-mm length T cut with a 3. 75-mm optical zone. A different optical zone would be necessary to correct a given amount of cylinder if the transverse incision length changed. 6. This steepening of the flatter meridian tends to negate a radial keratotomy, which is designed to flatten a steep meridian. Therefore, a compensatory factor must be added to the sphere of the refraction when RK and astigmatism are corrected together if the surgeon is aiming for emmetropia (Nordan rule). This compensatory factory is not large when dealing with small preoperative cylinder. This compensatory factor equals one half the preoperative cylinder, which means that I operate on the spherical equivalent not the spherical component when correcting a compound myopic astigmat by combined RK and astigmatic keratotomy. Since a mild undercorrection is desirable, the difference between the two approaches is not clinically significant for low degrees of astigmatism. Example:
•
This allows a surgeon to predict the amount of myopia induced because it equals the amount of steepening of the secondary meridian. This may be expressed as a percentage of the total astigmatism to be corrected.
- 2.00 - 1.50 x 180 0 Choice 1: Consider spherical component only a. RK: OZ to correct 2 D == 4.0 mm h. Jump T cut, OZ 7 mm/1.5 mm to correct 1.50 D of cylinder
Plano -9.00 x 90° Ruiz procedure T length 1.5 mm Postoperative: - 1. 00 sphere Surgeon's View
Eight diopters of change horizontally (flattening) is expected for every 1 D of change vertically (steepening). Therefore, the 9 D total of cylinder will be corrected by 9 (8/9) = 8 D horizontally and by 9 (1/9) = 1 D vertically. One diopter of myopia
Choice 2: Consider spherical component to be the spherical equivalent a, Consider as - 2,75 - 1. 50 x 180 0 (Nordan Rule) h. RK: OZ to correct - 2,75 D == 3.75 mm c, Jump cut, OZ 7 mm/ 1.5 mm to correct 1.50 D of cylinder
J CATARACT REFRACT SURG-VOL
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But now consider the following:
7.
-2.00 - 6.00 x 180°
-----I
RK OZ = 4.0 mm to correct 2 D of myopia Ruiz OZ = 3.5 mm to correct 6 D of cylinder I predict a result of -2.00 D, undercorrected sphere
8.
9. Nordan Rule -2.00 -6.00: Considers as a -5.00 -6.00 by adding 'h of the cylinder (3) to the sphere.
RK OZ = 3.0 with redeepening of radials at 5 and 7 to correct - 5.00 D. Actually only 2 D of myopia will be corrected.
10.
Ruiz OZ = 3.5 to correct ~6.00 D of cylinder. (The transverse length of a Ruiz with RK is always 1.5 mm to induce as little myopia as possible.)
11.
In other words, you must treat for 5 D to achieve 2 D in face of the Ruiz procedure, or "it's difficult to overcorrect sphere with a strong astigmatic keratotomy in position."
12.
It is interesting that both the jump end T cut of 6 mm, OZ 8 (Arrowsmith) and the radial 4 bare T cuts, 5 mm, (Ruiz) have essentially the same effect on the secondary meridian. The larger the cylinder correction, the harder it is to correct the spherical myopia. The maximum myopic spherical correction possible in conjunction with the Ruiz procedure is 3.5 D to 4.0 D. The effect of a transverse incision is indirectly proportional to its distance from the visual axis. For a 30-year-old - 6.00 - 4.00 x 180°, some compromise is necessary. Perform either a maximum 16-cut RK for spherical correction and attempt a T-cut procedure for astigmatism correction, expecting a result of plano - 2.00 x 180°, or use a stronger T-cut procedure for astigmatism combined with an 8-cut RK and expect - 2.00 sphere. I would pick the first alternative if uncorrected vision was to be maximized and the second alternative if contact lens wear was desired. Always use a Ruiz of l.5 mm T cut for compound myopic astigmatism because it induces the least myopia. Limit the transverse length of any astigmatic incision to 5 mm because a paradoxical flattening of the secondary meridian can occur with incisions longer than this. Keratometry postoperatively is often inaccurate after astigmatic keratotomy. The keratometer measures only one point of an aspheric cornea.
Each surgeon should be able to document his or her compensatory factor after analyzing several compound myopic astigmats who have been treated by combined RK and astigmatic keratotomy. Ajump end T cut, 6 mm, OZ = 8 mm (Arrowsmith) tends to steepen the secondary meridian by about one half to the full amount of flattening of the primary meridian. This causes either a mild hyperopic shift or no change in the spherical equivalent. Again, I would operate on the spherical equivalent for the RK portion of the procedure. Example: -2.00 - 3.00 x 180 0 Consider as
~3.50 ~3.oo
sphere x 180
RK OZ = 3.25 mm to correct ~3.50 D sphere
1----
T cut to correct 3.00 D cyl
.512
J CATARACT REFRACT
13. This aspheric cornea allows better uncorrected vision than expected when considering the patient's refraction. Also, presbyopes often experience inappropriately better reading vision along with excellent distance vision. 14. A residual myopia of - 0.75 Dafter RK will function the same as a-I. 50 D add and still allow 20/25 distance vision. Refractive astigmatism is equal to corneal astigmatism plus lenticular astigmatism (assuming normal posterior pole) in a vector sense. 15. Actual corneal change induced by an astigmatic keratotomy is equal to the postoperative corneal cylinder minus the preoperative corneal cylinder in a vector sense. Also, subtraction of the preoperative refractive astigmatism from the postoperative refractive astigmatism (in a vector sense) will establish induced corneal change.
SURG-VOL 12, SEPTEMBER 1986
Vector Analysis of Astigmatic Keratotomy
c R r---------=='*------ 180°
9(}0
9(}0
L
L
135°
135°
Pre-op Plano - 4.00 x K
= 41
9(}0;
@ 80°; C 44 @ 170°
Post-op plano - 1.00 x 45°; R = -1.00
R = -4.00
= -3.00
45° (post-op) KI
Induced corneal change = KI KI = (astigmatism post-op) - (astigmatism pre-op)
90° ------------~~~---------
R = Refractive astigmatic vector L = Lenticular astigmatic vector C = Corneal astigmatic vector
16. 17. 18.
19.
Axes are labeled one half their normal amount to allow addition of vectors without compensatory mathematics (Tate). Operate on the steeper keratometric meridian to avoid irregular astigmatism. Operate on the refractive astigmatic power to minimize postoperative cylinder. This is important when large amounts oflenticular astigmatism exist. Operating on the refractive axis is clinically acceptable because it usually corresponds closely to the steeper keratometric meridian, but be alert to occasional cases with large degrees of lenticular astigmatism. Irregular astigmatism refracts more hyperopic.
20. Irregular astigmatism is often associated with poorly healed incisions and will resolve in a few weeks as the incisions heal. 21. Irregular astigmatism after astigmatic keratotomy is basically an irregularity of the stroma that is reflected in the epithelium. The air-epithelium interface is the site of action but not the cause of the defect.
~----...~-' 22. Irregular astigmatism can be caused by epithelial disease, i.e., punctate keratopathy, bullous keratopathy.
J CATARACT REFRACT SURG-VOL
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23. Regular and irregular astigmatism may coexist. 24. Astigmatic keratotomy only treats regular astigmatism. CLINICAL PLANNING Thinking 1. Mid T cuts and jump cuts may be performed as singles -on only one side of the visual axis (Berkeley). 2. Bare T cuts and the Ruiz procedure should be performed on both sides of the visual axis. 3. If single T cuts are performed, the preferred location is under the upper lid or nasally. 4. Ruiz procedure - 3.5 OZ or greater to avoid glare and diplopia. 5. Astigmatic keratotomy should be centered about the visual axis, not the corneal center. 6. Avoid four-corner incisions; they cause increased scarring, pain, and recurrent erosion. 7. Consider treating astigmatism combined with RK at - 1.25 D with the rule, - 1.00 D against the rule. 8. Astigmatism correction is not greatly affected by age and lOP as is RK surgery.
Cutting 1. Mark visual axis accurately; a miotic pupil is valuable. 2. The proper meridian for an astigmatic procedure may be marked by a. Judgment and approximation (experienced surgeon) b. Microscope reticle (Fenzl) c. Circular marker (Mendez) Remember that the K readings, patient placement, microscope placement all have a 5 degree margin of error. 3. Use epithelial markers as indicated. 4. Use an ultrasound pachymeter to ensure consistent depth. In my opinion, 85% achieved depth of corneal thickness is optimal for transverse incisions. 5. Measure over or near PKP scars and change blade depth as necessary. Often scarred areas are thinner than the surrounding tissue. 6. A front-cutting blade should be used for long transverse incisions to allow maximum visibility. 7. A front-cutting diamond blade cuts to a depth of approximately 90% of corneal thickness. A bias of - 5% from corneal thickness is necessary to achieve an 85% depth cut. 8. It is useful to fixate the globe with a Kremer forceps at the meridian 90 degrees away from the operative meridian to ensure proper orientation. POSTOPERATIVE 1. Transverse incisions must gape to achieve significant astigmatic correction. 2. Patch with antibiotic ointment or drops until the epithelium is intact. 514
3. Do not use a T lens for seven to 10 days postoperatively because tight lens syndrome is common. 4. Lateral gape of Ruiz pseudoradial incisions is common after PKP. 5. Hyperopia caused by irregular astigmatism will resolve as the irregular astigmatism resolves.
ADDITIONAL ASTIGMATIC PEARLS 1. Astigmatism after PKP-reduce goal by 40%. If preop PKP astigmatism is + 6.0 D, aim for 3.5 D. 2. Ruiz procedure combined with cataract-adjust the IOL power for expected change in spherical equivalent. 3. Cataract after previous astigmatic keratotomy and RK-do your best routine cataract and IOL procedure but be sure to compute IOL power accurately. Two methods for IOL power calculations after astigmatic keratotomy include the following: (1) current K readings and axial length. Be aware of possible keratometry inaccuracies. (2) Compute IOL power by using original Ks and axial length. Compute the difference in refraction between preop and postop keratotomy. Add this difference to the computed IOL power. Until further advances are made, I recommend using both methods of determining IOL power after refractive surgery. Examples: Pre-keratotomy refraction: + 1.00 - 3.00 x goo K: 40x 43 @ 180° AL: 23.5 Post-keratotomy refraction: + 0.50 sphere K: 40.50 x 41 @ 180° AL: 23.5 Method 1: Using postop Ks: AL 23.5 Average K = 40.75 (40.5 + 41.(0) IOL = 21.50 D 2 Method 2: Using preop Ks and accounting for change in refraction from keratotomy procedure: AL 23.5 Postop refraction minus preop refraction spherical equivalent: + 0.50 - (-0.50) = +1.00 postop preop Original IOL power preop calculated at 23.5, K = 41.5, IOL = 20.5: 20.5 + 1.00 = 21.5 D In other words, the IOL power must compensate for the increase in hyperopia after RK or astigmatic keratotomy by becoming stronger than the original preoperative calculation would indicate. 4. Ruiz after RK-reduce goal by 40% as with PKP. 5. To determine if a patient needs an RK in conjunction with an astigmatic procedure, consider the following rule: Multiply the -cyl by 20% and algebrai-
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cally add this to the sphere value of the refraction. If the result is more myopic than - 0.50 D, then an RK based on spherical equivalent (adjusted by appropriate factors) is indicated ifthe goal is emmetropia.
CHARTS See Appendix A, B, C, D: These charts represent my philosophy of refractive surgery. CLINICAL EXAMPLES Several clinical examples are listed below with my preferred method of correction. The assumed goal is emmetropia in all cases. Of course, appropriate factors for each surgeon which pertain to the patient's age, lOP, sex must be taken into account. Preoperative Surgery 1. - 2.00 - 0.75 x 180° a) RK; no rx for cylinder 2. - 2.00 - 1.50 x 180°
7.
+ 3.00 - 6.00 x 180°
Ruiz; 3.5 mm OZ, 5 mm length at 90°
8. PKP with 8 D of astigmatism
Ruiz; plan for 5.0 D, length 2.5 mm
9. - 5.00 - 2.50 x 180°
a) RK for - 6.25 D b) double jump radial T cuts at 7.0 mm OZ, length 2.5 mm
10. RK post-op jump T cut at 7.0 mm OZ, + 0.50 - 2.00 x 180° 90° superior; reopen radials radials at 90° and 180° at 90° superior and inferior 11. RK post-op
+ 0.50 - 2.00
x 180° radials "off axis"
double radial bare T cut (Thorn ton, Jensen) and reopen adjacent radials
b) RK for -2.37 D
12. RK post-op + 1.00 - 5.00 x 180°
Ruiz; 2.5 mm, plan for 3.0 D
a) RK for -2.75 D b) single jump radial Tcut at 7 mm OZ; length 1.5 mm at 90° c) any of the T cuts will function well d) consider double bare T cut 7.0 mm OZ, 2.5 mm; rotate accordingly (Thornton, Jensen)
13. - 6.00 - 5.00 x 180°
Myopic keratomileusis and Ruiz procedure at 90°
3. - 2.00 - 3.00 x 180°
a) RK for - 3.50 b) double jump radial T cut, 7.0 mm OZ or double jump T cut, 7.0 mm OZ or double jump end T cut, 9.0 mm OZ, 6 mm length or double jump staggered T cut, 7.00 mm OZ, length 2.0 mm
4. - 2.00 - 5.00 x 180°
a) 6 cut RK for - 4.50 b) double straight 4 bare T cut, 1.5 mm length (straight Ruiz) at 90°
5. + 1.50 - 2.00 x 180°
a) 20-year-old; single jump radial Tcut at 7.0 mm OZ, length 2.00 mm at 90° b) 50-year-old; no surgery; presbyope and spherical equivalent will become more hyperopic with astigmatism correction
6. + 1.00 - 6.00 x 180°
Ruiz; 3.5 mm OZ, 2.5 mm length at 90°
14.
+ 2.00 - 4.00 x 180°
Ruiz; 5.0 mm length
15. Cataract 460.) 90° 43 @ 180°
manipulate wound by allowing recession at 90° to correct astigmatism
16. Cataract 46 @ 90° 40 0) 180°
double bare T cut at 7.0 mm OZ, 3.5 mm length, axis 90°; manipulate phaco wound as necessary under keratometric control to achieve appropriate postop corneal shape
17. Cataract 90° 40 46 @ 180°
double bare T cut at 7.0 mm OZ, 3.5 mm length, axis 180°; manipulate phaco wound as necessary under keratometric control to achieve appropriate pas top corneal shape
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CATARACT/IOL ASTIGMATISM CONSIDERATIONS Cataract surgery has been advanced immeasurably by the introduction of the IOL, especially the posterior chamber IOL. However, excellent results require that significant astigmatism be corrected or that minimal astigmatism be maintained. Intraocular lens surgery benefits from refractive surgery techniques. Astigmatic keratotomy and wound manipulation may be used at the time of surgery to minimize postoperative astigmatism (Martin, Maloney). Recession (loose suturing) of a cataract wound is more stable than a resection (tight suturing). The concept of always operating on the steep meridian and performing a wound recession is an excellent one, but many surgeons find operating from the side tedious (Terry). It is hoped that astigmatic keratotomy can allow surgery from above in all cases and provide enough astigmatic control so wound manipulation need not be pursued beyond its appropriate limits.
1.25 - 1.75 D
Double bare T cut with peripheral radial; OZ=7; length ofT cut= 3.5 mm 2.0 - 2.5 D
In cataract/IOL surgery, the approach to wound management is based on preoperative keratometry. The options available to the surgeon to correct astigmatism usually include the following possibilities: 1. Wound superiorly-tighten, neutral, loosen 2. Wound rotated temporally-loosen 3. Wound enlarged from normal choice (i. e., 3 to 6 mm; 6 to 12 mm) to gain increased astigmatic control 4. Wound plus astigmatic keratotomy
Double 2 bare T cut with step-ladder radial; OZ=7.9; length of Tcut= 3.5 mm
I believe that long-term correction of significant against-the-rule astigmatism (flatter meridian vertical) is not achieved by using tight sutures with a wound position along the flatter meridian. A loose wound (recession), on the other hand, allows the steeper meridian to flatten and does lead to more effective longterm astigmatism correction. The larger the wound, the larger the astigmatism correction possible up to the limit of maintaining a watertight wound. I assume the following approximate relationshps:
WOUND LENGTH
3 mm 6 mm 10-12 mm
MAXIMUM ASTIGMATIC CORRECTION BY LOOSENING
o diopters 2.5 diopters 4.5 diopters
The total amount of astigmatism correction obtained is determined by the wound's effect plus that of the keratotomy. I currently use three keratotomy patterns with cataract surgery and have assigned them a dioptric astigmatism correction value as follows: 516
4.0 - 5.0 D
Ruiz; OZ=4.25 mm; length of transverse=3.5 mm
Qualitative or quantitative keratometry during cataract surgery is possible after astigmatic keratotomy since the OZ is 7.0 mm. The relative relationship between the primary and secondary meridia is important, not the absolute number of the quantitative keratometer since the aspheric shape of the cornea may make this number inaccurate.
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Preoperatively the surgeon may plan for total astigmatism correction by considering the amount of astigmatism to be gained by a recession of the wound and then adding the specific astigmatic keratotomy necessary. During surgery the astigmatic keratotomy is performed before the anterior chamber is entered. The surgeon should maintain a conservative attitude and aim for a combined effect of perhaps one diopter less than the total preoperative astigmatic error. This allows an astigmatic keratotomy of the lowest value (and least number of incisions) to be used. The surgeon must be very confident of the predictability of his or her normal wound closure technique to allow for the anticipated cylinder changes
associated with this wound closure combined with the astigmatic keratotomy. Recently I have been using a simple intraoperative tonometer based on the Barraquer tonometer design, which ensures similar lOP during all keratometry measurements (Kratz). CONCLUSION Astigmatism is a problem that can effectively be approached by astigmatic keratotomy. Certainly, astigmatic keratotomy sophistication will improve in the future but currently it appears to be safe and quantifiable enough to establish it as a routine part of our surgical armamentarium. Many difficult astigmatic cases can now be tackled by concerned eye surgeons to benefit these deserving patients.
APPENDIX A
RUIZ TECHNIQUE - CORRECTION OF ASTIGMATISM DJOPTERS OF ASTIGMATISM
LENGTH OF STEP LADDER INCISIONS
(SMALL) 2.Smm
(LARGE) Smm
2
3
4
5
6
7
8
5.25 (-0.3)
4.75 (-0.5)
4.25 (-0.7)
3.75 (-0.9)
3.50 ( -1.0)
3.25 (-1.2)
3.00 (-1.3)
5.50 (-0.5)
5.00 (-0.8)
4.50 (-1.00)
4.00 (-1.3)
3.75 (-1.5)
3.50 (-1.8)
3.25 (-2.00)
INSTRUCTIONS REMEMBER: 1. 2. 3. 4. 5. 6. 7. 8. 9.
Refraction in negative cylinder format. Find column for diopters of astigmatism correction desired. Choose either middle or lower box of column depending upon amount of induced myopia desired (number in parentheses). The number above the parentheses is the proper optical zone. The box to the extreme left of the chosen row is the length of thestep-Iadder incision. Surgeon's own factor for patient age, etc., must be taken into account. If spherical component less than or equal to 0, then use 1.5 mm step-ladder incisions. Combine with radial keratotomy if desired. Adjust your technique according to your experience. This chart assumes incision depth of 80% depth for all incisions.
J CATARACT REFRACT SURG-VOL
RUIZ TECHNIQUE PERFORMED AT STEEPER MERIDIAN EQUALS AXIS OF PLUS CYLINDER REFRACTION OR 90° AWAY FROM NEGATIVE CYLINDER REFRACTION. FEET
90"
leo~3~S:800
.s:zrs?35
0
90°
HEAD RUIZ AT 90"
12, SEPTEMBER 1986
SURGEON'S VIEW
AUIZ AT 180 0
517
APPENDIX B
T-CUTS FOR ASTIGMATIC CORRECTION 1.75-2.25
1.0-1.50
DIOPTERS
OIOPTERS
GUIDELINES
1. No incisions intersect 2.
Place T-cuts above 180° meridian on cornea when possible.
3. Place staggered T-cuts al 7 mm oplical zone.
3.25-3.50
2.50-3.0
OIOPTERS
DIOPTERS
4. Change according 10 your experience.
5. Perform T -cuts in steeper meridian = axis of positive cylinder refraction or 90° away from axis of negalive cylinder refraction
SURGEON'S VIEW
APPENDIX D
APPENDIX C
COMBINED RADIAL KERATOTOMY
REFRACTIVE SURGERY SELECTION GUIDE
and
RUIZ TECHNIQUE
1985
-sph
GUIDELINES
-cyl
(original reiraction)
-cyl
'new' refraction for optical zone considerations
+
1. Refraction in negative cylinder format.
2. Find sphere on vertical scale. 3. Proceed horizontally to right until cylinder power reached.
H Y P E R 0
P I
A
4.
This location determines choiclI of surgery.
5.
Adjust chart to your preferences and experience.
7.0
0
P I
A
3.0 4.0 5.0 6.0 7.0 0 9. 0 10. 0 11.0
518
HKM+ RUIZ
HKM
6.0 5.0 4.0 3.0 2.0 1.0 0 1.0 2.0
M Y
-sph + 1_
9.0 8.0
RUIZ 1.5mml
H·EPI
RUIZ (4.5mm)
RK + RUIZ
RK
@ /1'
RK
+
@ /1.'-
MKM
T·CUT
8.0 8.5 7.0 7.5
~
r-----: _____ J
I
450
400
INSTRUCTIONS
--'-----j
C-----------;UIZ (2.5 mm) 0.5 10 1.5 2.0 2.5 3.0 3.5 \ 4.0 4.5 5.0 5.5
.00
C;II
cyl
J
1.
2. 3.
4. 5. 6.
Refraction in negative cylinder format. Use RUIZ with 1.5 mm tangential incisions. Choose optical zone for Ruiz.
Choose optical zone for 6 Incision RK based on 'new' sphere. Maximum limit of spherical correction equals 3.5 D. Change technique according to your experience.
375
325
300
REMEMBER:
RUIZ TECHNIQUE PERFORMED AT STEEPER MERIDIAN EQUALS AXIS OF PLUS CYLINDER REFRACTION OR (90·)AWAY FROM AXIS OF
MINUS CYLINDER REFRACTION.
~EET
"'.
,JSJ2:\':". .~350
MK+RUIZ
",'
MY·EPI
J CATARACT REFRACT
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