Staar Collamer posterior chamber phakic intraocular lens to correct myopia and hyperopia

articles Staar Collamer posterior chamber phakic intraocular lens to correct myopia and hyperopia Emanuel Rosen, MD, FRCSE, Christa Gore, MSc, MCOptom > __ • ___ _

~_ ,c _~~

i

_"

H ,,"._' __

~~_'''" ' 'W

.... w '''''

' W~W

"

W

"-

' ABSTRACT j, '

, ' PurpoSe; To evalt,Jatethe efficacy. safetY, stat>ility,an'd prediCtability ofimplanUng a ! ,

collagenpolymer(staat Collamei""'), ' posterior , cham~rphakic ' intraocui~lr lens (I0L) to Correct myopiaandhy~ropia; , ' . . Setting: Centre for Advanced Refractive Eye Surgery at the 8MI Alexandra Hospital, Cheadle" Manchester, United Kingdom.

Methdds: AStaar Collamer posterior chamber'.phakic IOL was implanted in 25 eyes of 14 patients With a mean age of 37.9 years (range 20 to 50 years). Seven patients

were

were men and seven, women. Sixteen myopic and .9, hyperopic. Before treatment, eaCh patient had a thorough evaluation including refractive, general, examination included visual acuity, ocular, andsooial and "personalhrstories; "reftaction,ton'ometry; tOpOgraphy, biornetry;biomicroscbpy, pupil SiZe in dim illumination, and posterior segment eValuation byavifreoretinal specialist. j:iatients were informed about the surgical proceSs ,and expectect outcome,their own expectations were discussed, and tMit consent f\:>. surgery was obtained.'Surgical implantation was pe~ormedthroughaless than 3.0 mm clear corneal sutureress incision using brief generalahesthesia on a day-case surgical basis.

Tna,

Results: At 3 months postoperatively, all eyes had .a.significant increase in uncor~ rected visual acuity, allowing all but two patients (three eyes) to manage>most ; .. .. activities without spectacles. AdjustrTiehtby~jn6isiol"lal corneal slirgerywas planned · forunderc6rteCtedmyopic eyes(n .:. 3»Pupil block glaucoma and ·pigr'l1ent deposits occurred in one patienteach.

Conclusion: In this short-term study, the posterior chamber phakic IOl was predictable, safe, and efficacious in the correction of myopic and hyperopic refractive errors, with good refractive stability. Long-term follOW-liP i$·requiredto ·yalidate thatlhe absence.ot significant complications in most. patients is a lasting phenomer&oh.J Cataract Refract Burg 1998;' 24:596-606

D

efractive surgical solutions for the correction of Rmyopic, hyperopic, and astigmatic errors embrace two principal anatomical opportunities: the cornea and lens. The cornea effects about two thirds of the refracReprint requests to Emanuel Rosen, MD, lOSt. John Street, Manchester M3 4DY, United Kingdom.

596

tive power of an eye and the crystalline lens the balance. Although the cornea is accessible, it is a delicate and precise optical instrument designed to minimize optical aberrations, and it maintains a lifelong refractive stability. It is approximately 0.5 mm thick in its central portion. Almost all refractive surgical interventions in the cornea are irreversible, with intrastromal corneal

) CATARACT REFRACT SURG-VOL 24, MAY 1998

PHAKIC PC IOL FOR MYOPIA AND HYPEROPIA

ring segments the exception. All corneal refractive surgery, whatever its form, is invasive and subject to problematical if rare complications. In contrast, the crystalline lens changes throughout life, leading to presbyopia and other refractive changes thereafter. The minimally invasive refractive lens surgery generally carried out today under the guise of refractive cataract surgery is effective, safe, predictable, and stable. Patients who retain accommodation but have significant refractive errors are now able to retain that accommodative power by having refractive surgery using a biocompatible, supplementary, posterior chamber phakic intraocular lens (IOL), known in marketing terms as an internal or implantable contact lens. Although this term is inaccurate in optical terms, it conveys to patients the general concept of a permanent or semipermanent neutralization of their refractive error and therefore will pass into common usage. The use of a supplementary IOL allows retention of the crystalline lens function until its replacement is indicated, when the posterior chamber phakic IOL should be easily removed. This study evaluated the surgical and refractive aspects of posterior chamber phakic IOL implantation.

Patients and Methods The Staar posterior chamber phakic IOL was designed for the surgical correction of moderate to high hyperopia and myopia with a range of correction from + 10.00 to -20.00 diopters (D). The IOL is placed in the posterior chamber anterior to the crystalline lens, retaining the accommodation of the crystalline lens. The lens material is a proprietary hydrophilic collagen polymer with a water content of 34%, a light transmission of 99%, and a refractive index of 1.45. The lens can be folded and inserted through a sutureless corneal incision smaller than 3.0 mm. The IOL is 60 Il111 thick, and its optical zone varies between 4.5 and 5.5 mm according to the power required. The length of the IOL is tailored to each eye individually by relating lens length to the horizontal white-to-white length. In hyperopic eyes, the estimated lens length is reduced by 0.5 mm and in myopic eyes, extended by 0.5 mm; experience has shown that these variations from the horizontal diameter of the anterior segment avoid implantation of lenses that are too large

or small. A lens that is too large would cause undesirable vaulting, and a lens that is too small could become decentered. The phakic IOL is supplied sterile in a solution contained in a glass vial in a paper pouch individually packaged and labeled with product information. It is steam sterilized, and sterility is assured if the pouch and the vial seals are intact and the time is within the indicated expiration date. The power required for each eye is calculated by Staar Surgical AG, who supplies the lens, and it can be confirmed by use of the 1997 Holladay IOL power calculation program.1-3 A minimum ultrasonically measured anterior chamber depth of 2.8 mm is recommended for the IO[s implantation. Assessment of the posterior segment in eyes with pathological myopia by a vitreoretinal specialist was done to ensure that these eyes were documented and if necessary treated for retinal pathology that might lead to retinal detachment. In our opinion, implantation of a posterior chamber phakic IOL per se should not influence retinal detachment occurrence, and future experience should show whether this opinion is verified. Nevertheless, these eyes deserve expert evaluation to minimize the prospect of coincidental retinal episodes. The Staar CollamerTIol posterior chamber phakic IOL was implanted in 25 eyes of 14 patients with a mean age of 37.9 years (range 20 to 50 years). Seven patients were men and 7, women.

Surgical Procedure Before lens implantation, a neodymium:YAG (Nd:YAG) laser iridotomy was performed in the upper peripheral iris. Two iridotomies were placed 90 degrees apart to preclude the possibility of pupil block after IOL insertion. The Nd:YAG surgery was done at least 2 weeks before IOL implantation to allow the minor post laser anterior segment inflammation to subside. All lens implantations were done on an outpatient basis using general anesthesia with a laryngeal mask to maintain the airway and infusion of the anesthetic propofol (Diprivan®). The anesthesia method was based on patient and surgeon preference. At least 5 minutes before surgery, the eye was irrigated with povidone-iodine 5% (Betadine®) to destroy commensal bacteria. The eyelids, eyelashes, and skin surrounding the eyes were prepared in a like manner. The patient's face was covered with a sterile

J CATARACT REFRACT SURG-VOL 24, MAY 1998

597

PHAKIC PC IOL FOR MYOPIA AND HYPEROPIA

drape, and the eyelashes were tucked under the drape and clipped into place by the speculum used to maintain visibility of the eye during surgery. Maximal mydriasis, which is required for the procedure, was achieved using a combination of mydriatic topical medications. Once the surgical drape was placed on the patient's face and eye but before it was opened, the IOL was removed from its container and loaded into the cartridge for insertion into the eye. The IOL loading was complicated and will remain so until the lens is prepackaged in a form in which it can be injected into the eye. The cartridge, with a fine nozzle that was inserted through the clear corneal incision, was lubricated with sodium hyaluronate (Healonid®). The IOL was placed in the body of the cartridge so that its superior surface was uppermost when the lens was injected into the eye's anterior chamber. Because the IOL is very thin, it was handled extremely carefully as it was moved from the body of the cartridge into the nozzle. When loaded, the cartridge was placed in an injector system wherein a plastic plunger pushed the IOL forward through the nozzle and into the anterior chamber. To protect the IOL, a piece of surgical sponge was used as an interface between the hard plastic material of the plunger and the 101. Care was taken during implantation to ensure no sponge material entered the eye. At this point the surgical drape was opened and the speculum placed to ensure that eyelids and eyelashes were thoroughly entrapped by the adhesive plastic material of the surgical drape. Initially, two 0.8 mm paracenteses were placed 90 degrees from the clear corneal tunnel incision to facilitate immediate replacement of aqueous humor by the viscoelastic gel and to provide access for the IOL positioning spatula. The IOL incision comprised a 2.6 X 1.5 mm, self-sealing clear corneal tunnel. In eyes in which pre-existing astigmatism was being adjusted, an arcuate component was introduced to the clear corneal tunnel incision commensurate with the degree of astigmatism. The process was identical to that used in similar circumstances in clear corneal incisions for cataract surgery. Accordingly, such incisions were placed on the steep axis of the corneal astigmatism. During surgery, care was taken to prevent the surgical instruments from touching the corneal endothelium, crystalline lens capsule, or iris diaphragm. The 598

use of Healonid protected the tissue and allowed the IOL to unfold in a controlled manner and later to be manipulated into position in a precise manner to minimize surgical trauma. As the IOL unfolded slowly in the viscous material in the anterior chamber, its orientation was checked for the IOL is vaulted. (If at this point its orientation is incorrect, it must be removed and replaced, a situation that did not occur in this series.) When the IOL unfolded (Figure 1), its four foot plates initially lay anterior to the dilated iris diaphragm. Each foot plate in turn was gently levered into position behind the iris through the pupil with a long spatula without placing pressure on the crystalline lens. Then, viscoelastic was removed from the anterior chamber and exchanged for acetylcholine chloride (Miochol®), causing the pupil to constrict and trap the IOL in the posterior chamber. Most of the viscoelastic was removed to avoid a postoperative increase in intraocular pressure (lOP). The clear corneal tunnel incision was self-sealing after infusion of its edges with balanced salt solution. Figures 1 to 3 show the IOL at different stages intraoperatively. No unusual postoperative anesthesia complications occurred. Recovery was rapid, and all patients were discharged within 3 hours of surgery. Postoperatively, a steroid/antibiotic combination eyedrop was recommended three times daily for a week. Each patient was observed on the first postoperative day and a few days later, at which point medication was

Figure 1. (Rosen) The posterior chamber phakic IOL is delivered from a cartridge nozzle and rolled into a tube in the anterior chamber amidst viscoelastic, which aids the controlled unfolding process.

J CATARACT REFRACT SURG-VOL 24, MAY 1998

PHAKIC PC IOL FOR MYOPIA AND HYPEROPIA

Table 1. Best corrected visual acuity over time and the corresponding safety index.

Myopic group

Figure 2. (Rosen) The phakic 10L in situ in the posterior chamber as the Healonid is exchanged for a balanced salt solution.

tapered. Longer-term follow was arranged to enable full documentation of outcome in all cases.

Results Safety Safety was evaluated by companng preoperative best corrected visual acuity (BCVA) with that at 3 months postoperatively. If there was no loss of acuity, the procedure was deemed safe from the refractive perspective. The BCVA results are shown in Table 1. No eyes lost more than one line of BCVA. In the myopic group, one eye lost one line of BCVA, six eyes

cal

00

15

20

20

75

cal

as

20

20

20

100

DRS

00

15

15

133 160

100

DRS

as

20

15

ESD

00

40

25

HES

00

20

20

20

100

HES

as

25

25

25

100

LED

00

30

25

25

121

LlJ

125

00

50

40

40

LlJ

as

60

60

50

121

LYJ

00

15

15

15

100

LYJ

as

20

15

15

133

MaS

00

20

15

133

MaS

as

20

15

133

Raj

00

20

20

125

Raj

as

30

30

82

DOS

00

30

25

121

DOS

as

20

20

100

HIB

as

30

25

Hyperopic group

40

121

LEK

00

25

15

LEK

as

25

15

LID

00

15

20

20

75

LID

as

15

15

15

100

WIJ

00

15

15

100

WIJ

as

15

15'

100

166 166

BCVA = best corrected visual acuity 'Snellen denominator at 20 feet t(Post/Pre Decimal Acuity) x 100: mean = 115, myopic group; 116, hyperopic group 'Result at 1 month, before 10L was removed

Figure 3. (Rosen) Slitiamp optical section photograph showing the vaulting of the 10L (arrow) over the center of the crystalline lens.

gained one line, one eye gained two lines, and eight eyes remained unchanged. In the hyperopic group, one eye lost one line of BCVA, two eyes gained one line, two eyes gained two lines, and four eyes remained unchanged. Table 1 shows a safety index calculated by dividing the postoperative decimal Snellen acuity by the preoperative decimal Snellen acuity. Although not

J CATARACT REFRACT SURG--VOL 24, MAY 1998

599

PHAKIC PC IOL FOR MYOPIA AND HYPEROPIA

Table 2. Spherical equivalent over time.

i ,;~ Eq~t(D) I'

'\ '

Pat!...

i:ye

' . '1-:.,'~

'

P08toperatiVeIy

· : ; .~r~~

t'Qnth

~~t~

$~th.

-0.25

+1.00

+1.00

+1.00 -0.12

Myopic group aD

-6.87

cal

as

-7.75

0.00

-0.25

-0.12

DRS

aD

-5.50

-0.25

-0.25

-0.25

-0.25

DRS

as

-5.50

-0.75

-0.37

-0.23

0.00

ESD

aD

-10.00

-1.75

-2.37

-2.25

-2.12

HES

aD

-8.00

+0.12

-0.37

-0.37

HES

as

-13.37

-0.75

-1.25

-1.75

-2.12

-1.12

-1.12

-1.00

-1.00

-0.87

cal

-0.37

LED

aD

-12.25

LlJ

aD

-7.75

-1.12

-0.25

+0.25

+0.25

+0.62

LlJ

as

-5.25

-0.50

-0.25

+0.12

+0.12

-0.62

LYJ

aD

-11.50

-1.12

-0.50

-1.12

-1.37

LYJ

as

-12.25

-0.50

-0.25

-0.25

-0.37

MaS

aD

-8.00

-0.75

-0.62

0.00

-0.37

MaS

as

-7.62

+0.12

-0.75

-0.25

-0.62

Raj

aD

-14.50

-4.00

-4.25

-4.25

Raj

as

-12.50

-2.75

-2.50

-2.50

DOS

aD

+2.25

0.00

-0.62

DOS

as

+4.87

+0.25

+0.50 +1.00

Hyperopic group

-0.12 +0.50 +0.50

+1.00

HIS

as

+4.00

+1.00

LEK

aD

+5.12

0.00

0.00

-0.37

LEK

as

+4.75

-0.75

-0.75

+0.25

LID

aD

+5.62

-0.12

+0.12

+0.37

+0.12

-0.12 +0.12

0

LID

as

+4.37

-0.75

-0.62

0.00

+0.37

WIJ

aD

+4.25

+0.25

+0.25

+0.25

+0.25

WIJ

as

+4.25

0.00

0.00

0.00'

Note: - indicates data not available 'Phakic 10L removed at 1 month

strictly mathematically correct, the index gives an indication of outcome at a glance. If the index figure is less than 100, the preoperative BCVA was better than the postoperative BCVA and vice versa.

Stability Spherical equivalent refractions preoperatively and at least 3 months postoperatively (except for patient WI], left eye, 1 month results) are shown in Table 2 and Figure 4. 600

Efficacy Efficacy was evaluated by comparing preoperative BCVA with postoperative uncorrected acuity (UCVA). The manifest refraction and UCVA before and after all surgery are shown in Table 3. An efficacy index was used in the same way as the safety index in Table 1. If the index is less than 100, postoperative UCVA was less than preoperative BCVA and vice versa. Improvement in UCVA is the object of the exercise, bearing in mind that residual myopia for enhanced near vision may be

J CATARACf REFRACf SURG-VOL 24. MAY 1998

PHAKIC PC IOL FOR MYOPIA AND HYPEROPIA

~ ~t-----~~~tr----------------~======~.-----------~

i

c:

m II: ~

~ ~~--~~~~----------------------------------------~ -10

~--4-,ffI-+------------------------------------~

-12 ~---IH-+-------------------------------------~ -14 ~--+---------------------------------------------~ -16 " - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Visit A

Figure 4. (Rosen) Refractive stability in the myopic (A) and hyperopic (B) groups (n = 16 and 9, respectively)_

~ c:

o

n ~ II: W

CJ)

-f+-----------------------------------------------------~ -2~----------------------------------------------------~

Visit

B

an objective in near presbyopic eyes. In the myopic group at 3 months postoperatively, four eyes achieved a UCVA of 20/20 or better, six eyes 20/25 or better, nine eyes 20/40 or better, and seven eyes less than 20/40. In the hyperopic group, four eyes achieved a UCVA of 20/20 or better, seven eyes 20/25 or better, eight eyes 20/40 or better, and one eye less than 20/40.

Complications In this series, one patient suffered significant complications, a 26-year-old man (WI]) with 5.00 D of hyperopia and brown irides. He developed pupil block glaucoma in his right eye 3 weeks postoperatively caused by functional closure of the laser iridotomies.

An immediate surgical iridectomy was performed through the initial clear corneal incision using a microvitrector under Healonid deepening of the anterior chamber. There was immediate recovery and no visual deficit. The fellow eye was checked and was functioning normally until 3 weeks later, when a similar pupil block episode occurred during the night. Immediate repeat Nd:YAG laser iridotomy enhancement seemed to deepen the chamber with an obvious flow of aqueous through the retreated iris fenestrations. The patient was hospitalized overnight and prescribed acetazolamide (Diamox®), timolol maleate (Timoptol®), and intravenous mannitol. Despite hypotensive therapy and apparent relief of the pupil block, retrociliary secretion

J CATARACT REFRACT SURG-VOL24, MAY 1998

601

PHAKIC PC IOL FOR MYOPIA AND HYPEROPIA

Table 3. Manifest refraction over time and the related efficacy index.

Myopic group

+0.25 + 1.50 x 80

+0.25 + 1.50 x 80

1200

40

38

-0.25 +0.25 x 120

-0.25 +0.25 x 120

1200

25

80

-0.50 +0.50 x 50

120

15

100

-5.50

-0.25 +0.50 x 20

120

15

133

00

-10.25 +0.50 x 130

-3.00 +1.75 x 120

1200

60

66

HES

00

-8.50 +1.00 x 10

-0.75 +0.75 x 10

-0.75 +0.75 x 10

1200

20

100

HES

OS

70

36

15

x 10 -1.75 +1.75 x 15

1200

00

1200

70

44

LlJ

00

100

0 .00 +1.25 x 75

400

60

82

LlJ

OS

x -1.75 +1 .50 x -0.50 + 1.50 x -0.75 +1.75 x

-2.50 +0.75

LED

x 175 -13.50 +2.50 x 10 -10.00 +5.50 x 90 -7.75 +5 .00 x 90

100

-1 .50 +1.75 x 100

200

60

100

LYJ

00

-12.00 +1.00 x 95

-1.75 +1.25 x 90

-2.00 +1.25

1200

LYJ

OS

-13.00 +1 .50

-0.50 +0.50

00

x 90 -1.50 +2.25 x 20

-0.75 +0.75

MOS

x 85 -9.00 +2.00 x 40

MOS

OS

-8.75 +2.25 x 165

ROJ

00

ROJ

COl

00

-7.25 +0.75 x 40

COl

OS

-8.50 +1 .50

DRS

00

-5.50

DRS

OS

ESD

x 140

-13.75 +0.75

-2.00 +0.50

25

x 90 x 90

30

50

1200

15

133

1200

30

66

-1.50 +1.75 x 170

1200

25

80

-15.00 +1.00 x 100

-4.75 +1.00 x 90

1200

400

6

OS

-13.00 + 1.00 x 60

-2.50

1200

400

6

DOS

00

-0.75 +1 .25 x 60

DOS

OS

x 90 +3.50 +0.50 x 90

HIB

OS

+3.50 + 1.00 x 60

0.00 +2.00 x 75

LEK

00

+4.75 +0.75

LEK

OS

+4.75

LID

00

+5.25 +0.75

x 80

-0.25 +0.75 x 80

LID

OS

+4.00 +0.75 x 85

0.00 +0.75 x 80

WIJ

00

+4.50 +0.50 x 165

WIJ

OS

+4.50 +0.50 x 5

Hyperopic group

+ 1.00 +0.50

x

100

0.00 +1.00 x 105 -0.75 +2.75 x 40

0.00 0.00 +0.50 x 90

25

25

121

80

25

80

400

70

44

40

15

166 166

40

15

x 90

200

30

49

-0.25 +0.75 x 75

100

25

60

0.00 +0.50 x 180

20

20

100

0.00*

20

15

100

-0.25 +0.25

UCVA = uncorrected visual acuity 'Snellen denominator at 20 feet t(Oecimal UCVA 3 Months Postop/BCVA Preop) x 100: mean = 70, myopic group; 98, hyperopic group *Result at 1 month, before 10L was removed

of aqueous humor must have occurred for within 2 hours the patient was in pain with high lOP. At immediate surgery, a surgical iridectomy was succeeded by failure of the anterior chamber to deepen. The situation could only be resolved by a vitrectomy and lensectomy. The IOL was removed at this time, and replacement by a 30.00 0 IOL was delayed for 6 weeks. During this time, the eye was not troubled by 602

inflammation or any other problem. This experience indicated that a significant opening of the brown iris, particularly in hyperopic (small) eyes, is a necessity and is probably best performed at the time of IOL implantation and at a location that can be seen to be away from possible occlusion by the IOL. In another patient (blue irides) who had excellent visual function and no subjective complaints, very fine

J CATARACT REFRACT SURG-VOL 24, MAY 1998

PHAKIC PC IOL FOR MYOPIA AND HYPEROPIA

more than 0.50 D. In the hyperopic group, 8 of 9 eyes achieved a correction within ±0.50 D of that intended; 1 eye was undercorrected by more than 0.50 D.

Discussion Refractive Surgery

Figure 5. (Rosen) Fine pigment deposits on the IOL surface 3 months postoperatively in an eye with 20/20 UCVA.

pigment deposits were noted on the IOL surface 3 months postoperatively (Figure 5 and 6). There was no degradation of image quality. Intraocular pressure was normal, and no pigment deposits were noted in the angles of the anterior chamber. Other complications included one case of transient corneal edema, minimal postoperative flare (no cells in all cases), reports of subjective edge glare and halos, and three significant undercorrections in the myopia group.

Predictability Figure 7 shows the intended versus achieved correction in all eyes. In the myopic group, 9 of 16 eyes were within ±0.50 D of the intended correction. Six eyes were undercorrected by more than 0.50 D and 1 eye, by

Figure 6. (Rosen) Slit photography of the eye in Figure 5.

Many adults are discomforted by their refractive error and poor UCVA. Although external aids in the form of spectacles or contact lenses are acceptable to the majority, several factors provide an indication for the consideration of a permanent solution in the form of refractive surgery. These include aging and other causes of contact lens intolerance, occupational requirements, sporting and other leisure interests, physical problems wearing glasses, and a psychological (self-image) desire to achieve the visual freedom refractive surgery is able to confer. Throughout this decade various techniques, some complementary and others overlapping, have been introduced that are able, either individually or in combination, to solve most if not all regular refractive errors in otherwise healthy eyes with acceptable predictability, safety, and permanence.4-11 The posterior chamber phakic IOL used in this study is an addition to the portfolio of refractive surgical interventions. It is a potentially reversible procedure but one in which the possibilities of complicating cataract formation, pigment dispersion, and pupil block glaucoma coexist. Like all refractive surgical procedures, whether corneal or lenticular, it is invasive and therefore carries small but definable general risks such as inflammation and infection. The use of a rigid aseptic technique is essential, and every effort must be made to eliminate the prospect of infection throughout the surgical procedure. This involves performing the surgery in an operating theater in which all the procedures are used to maintain sterility of the environment and of the surgical procedure itself. Posterior chamber phakic IOL implantation using lenses of other materials, such as silicone, have been reported unfavorably. Thus, the prospects for a potentially more biocompatible material in this location in the eye is eagerly awaited by many. Our results are encouraging; however, the short period of postoperative observation is readily acknowledged. The results provide a basis for further clinical experience and development. Every new technique

J CATARACf REFRACf SURG-VOL 24. MAY 1998

603

PHAKIC PC lOL FOR MYOPIA AND HYPEROPIA

e: c 0

U ~

(5

()

"C Q)

>

.~

.s::.

«

()

16 14 12 10

overcorrected

8

6 4 2 0

o

---- --2

~

4

~

----:

-

--.:- ....... ~

undercorrected

10

8

6

---

~:

12

14

16

Intended Correction (D)

A

e: c

o

:e~ .... o

()

"C Q)

~

7····················································...........................................................~ 6 5 4

~

•

~

overcorrected ~

...

Figure 7. (Rosen) Intended ver· sus achieved correction in the myopic (A) and hyperopic (B) groups (n = 16 and 9, respectively). Data are from the 3 month visit with the exception of that for the left eye of patient WIJ, for whom the results are at 1 month.

3+-------------···~-.~~---------d~--~d----~ ____ • un ercorrecte 2~-----____ ---=-=~~--------------------~

:E ()

«

o

1

2

3

4

5

6

7

Intended Correction (D)

B

using new technology needs the gradual accumulation of postoperative data without exposing a large population to its potential hazards. Time is required to evaluate the risk elements. If cataract for example became a consequence of posterior chamber phakic 10L implantation after a number of years, lens extraction and 10L implantation could follow without loss of visual function. If pigment dispersion has a time factor (and it has not been reported since the early prototype posterior chamber phakic 10Ls were implanted 4 years ago) and telltale signs were to appear, explantation of the 10L might be required. Therefore, the potential reversibility or adjustability of the technique are virtues that are absent from other techniques such as corneal refractive surgery (intrastromal corneal ring segments apart). No refractive surgical technique is entirely predictable. Therefore, patients about to have posterior chamber phakic 10L implantation should be aware that refractive surgery may be a staged process, in this case requiring minor corneal refractive surgical adjustments by radial keratotomy or laser thermal keratoplasty for example. 604

Historical Perspective Procedure development dates back to the initiative of Harold Ridley of St. Thomas' Hospital, London, who in 1949 initiated the process of pseudophakia, the replacement of the cataractous crystalline lens by a Perspex 10L. 11 ,12 The idea of aphakic 10L to supplement the function of the crystalline lens was explored in the mid-1950s by Joaquin Barraquer in Spain and Strampelli in Italy, among others. 13 Although their inventiveness was to be applauded, the reality was different. Neither the techniques nor the technology to make the process a success were available, and the pathophysiological consequences of implantation were not appreciated.

Anterior Chamber Phakic Iemes In the mid-1980s Georges Ba'ikoff in France, following the lead of experience with anterior chamber, angle-supported, clinical quality Perspex 10Ls to correct aphakia, devised lenses of high minus power for phakic implantation to treat moderate and high myopia. 14 The initial design was flawed and led to progressive loss of corneal endothelial cells as well as unaccept-

J CATARACT REFRACT SURG-VOL 24, MAY 1998

PHAKIC PC IOL FOR MYOPIA AND HYPEROPIA

able ovaling of the pupil.l 5 As the clinical experience gathered, a second generation of the Ba"ikoff high minus lens for myopia was produced that overcame the disadvantages of the first-generation lens to a large extent, but not completely. Corneal endothelial cell loss was averted by the elimination of corneal touch by the lens optic. The vault, size, and form of the lens were altered, but pupil ovaling continued, and the physiological eccentricity of the pupil combined with the small size of the optic (4.5 mm) led to visual phenomena such as halos and night glare. The surgical process involves an incision of significant size in relation to the limitation of the refractive effects of the surgery.I6-19

Posterior Chamber Phakic Lenses As the study of biomaterials developed, Svyatoslov Fyodorov in Moscow produced a lens enabling him to achieve a previously unimaginable feat; namely, the placement of a thin phakic 10L in the posterior chamber between the crystalline lens and the iris diaphragm, centered on the pupil,2° The prospective postoperative complication of pupil block glaucoma was averted by a peripheral iridectomy. Cataract formation, which would occur by contact of the lens material with the crystalline lens or instrument damage at the time of surgery, remained a negative factor in the minds of most ophthalmologists, who nevertheless appreciated the novelty and brilliance of the concept. Fyodorov experimented with biomaterials derived from collagen, a naturally occurring substance, and those who visited his institute in Moscow saw posterior chamber phakic lens implantation and examined patients who had had the treatment for myopia or hyperopia. Visitors to Moscow were impressed, at least with the short-term outcome of his surgery, and the Staar company of the United States acquired the patent for the production of posterior chamber phakic 10Ls. A subsidiary company, Staar Surgical AG of Switzerland, was set up, and this company refined the material for the lens. Thereafter, in conjunction with surgical experts, principally Roberto Zaldivar, MD, the lens design was finalized through a sequence of prototypes, which Zaldivar implanted and studied at his facility in Mendoza, Argentina. The international surgeons who had visited Fyodorov's institute in 1992 visited Mendoza, Argentina, in 1995. They observed several surgeries, examined

many patients postoperatively, and had a frank and full discussion of the clinical outcomes, including the remarkably few complications. It was realized that two small laser iridotomies 90 degrees apart prevent pupil block glaucoma. The question of lens sizing was also resolved and 10L power calculation refined. Subsequently, the process has proceeded without significant complications. Because the optic size of the posterior chamber phakic 10L varies between 4.5 and 5.5 mm, patients whose pupils enlarge beyond that size in dim light conditions may be subject to minor halos or night glare problems, phenomena that would also trouble a patient if the lens optics were decentered. Postoperative inflammatory activity within the eye has been minimal, which is a tribute to the biocompatibility of the proprietary collagen polymer Collamer and the atraumatic nature of the surgical technique. 21

Indications for Posterior Chamber Phakic Implantation The Staar posterior chamber phakic 10L was designed for the surgical correction of moderate to high hyperopia and myopia with a range of correction from + 10.00 to -20.00 D. The 10L is placed in the posterior chamber anterior to the crystalline lens, retaining accommodation of the crystalline lens. The 10L is most effective when the patient is able to use the accommodation of the crystalline lens. Thus, it is ideally implanted in younger patients; however, those who are in the early stages of presbyopia may benefit from its implantation, prolonging unaided near vision. Its advantage in presbyopic eyes must be weighed against the alternative of lens extraction and replacement with a monofocal or multifocal 10L. Patients with significant hyperopia may also benefit from implantation of a posterior chamber phakic 10L. Hyperopic eyes are generally smaller. Although an eye may have a shorter axial length, it may have an anterior segment of average dimensions, allowing successful implantation of the phakic lens. When hyperopia is caused by a flatter than usual cornea or an anterior segment of insufficient size, implantation of the 10L is precluded. Myopia up to 20.00 D is corrected by the phakic 10L; beyond that range, the myopic element must be supplemented by a corneal refractive procedure such as laser in situ keratomileusis. Co-existing astigmatism can be neutralized at the time of surgery by corneal incisional methods primarily

J CATARACf REFRACf SURG-VOL 24, MAY 1998

605

PHAKIC PC IOL FOR MYOPIA AND HYPEROPIA

using vanatlOn on the incision through which the posterior chamber phakic IOL is implanted.

Contraindications A history of ocular pathology is a general contraindication to posterior chamber phakic IOL implantation. Specifically, implantation should be avoided when the corneal endothelium is not healthy or if the cornea has a dystrophy causing abnormal shape (e.g., keratoconus) that would not be corrected by aphakic IOL. The presence of lens opacities or early cataract formation in the operative or fellow eye should be regarded as a contraindication, as should a history of iritis even if quiescent. Glaucoma and pigment dispersion syndromes and pseudoexfoliation of the lens capsule are absolute contraindications, as is diabetic eye disease. Pupil size is a critical factor in refractive surgery in general, and posterior chamber phakic IOL surgery is best avoided in patients who have particularly large pupils in dim illumination. Current Study Although the follow-up in our study was relatively short, patient acceptance of the procedure has been enthusiastic and appreciative. The visual effects were immediately apparent, and little medication was required as the surgery involved minimal trauma. Longer follow-up data are needed to confirm the good results regarding safety, stability, and predictability.

References 1. Holladay JT. Refractive power calculations for intraocular lenses in the phakic eye. Am J Ophthalmol 1993; 116:63-66 2. Holladay JT. Standardizing constants for ultrasonic biometry, keratometry, and intraocular lens power calculations. J Cataract Refract Surg 1997; 23;1356-1370 3. Holladay JT, Gills JP, Leidlein J, Cherchio M. Achieving emmetropia in extremely short eyes with two piggyback posterior chamber intraocular lenses. Ophthalmology 1996; 103:1118-1123 4. Verzella E High myopia: in-the-bag refractive implantation. Ophthalmic Forum 1985; 3:174-175 5. Praeger DL. Phakic myopic intraocular lens-an alternative to keratolenticulorefractive procedures (letter). Ann Ophthalmol 1988; 20:246 6. Werblin TP. Should we consider clear lens extraction for routine refractive surgery? Refract Corneal Surg 1992; 8:480-481

606

7. Goldberg ME Clear lens extraction for axial myopia; an appraisal. Ophthalmology 1987; 94:571-582 8. Fechner PU, Strobel J, Wichmann W. Correction of myopia by implantation of a concave Worst-iris claw lens into phakic eyes. Refract Corneal Surg 1991; 7:286-298 9. Praeger DL, Momose A, Muroff LL. Thirty-six month follow-up of a contemporary phakic intraocular lens for the surgical correction of myopia. Ann Ophthalmol 1991; 23:6-10 10. Fechner PU, Wichmann W. Correction of myopia by implantation of minus optic (Worst iris claw) lenses into the anterior chamber of phakic eyes. Eur J Implant Refract Surg 1993; 5:55-59 11. Ridley H. Intra-ocular acrylic lenses. Trans Ophthalmol Soc UK 1951; 71:617-621 12. Ridley H. The cure of aphakia, 1949. In: Rosen ES, Haining WM, Arnott EJ, eds, Intraocular Lens Implantation. St Louis, MO, CV Mosby, 1984; 37-42 13. Rosen ES, Haining WM, Arnott EJ. Intraocular Lens Implantation. St Louis, MO, CV Mosby, 1984 14. Baikoff G, Joly P. Correction chirurgicale de la myopie forte par un implant de chambreanterieure dans l' oei! phake. Bull Soc Belge Ophtalmol1989; 233:109-125 15. Baikoff G, Colin J. Damage to the corneal endothelium using anterior chamber intraocular lenses for myopia (letter). Refract Corneal Surg 1990; 6:383 Cotinat J, Renard G, et al. Damage to the 16. Saragoussi corneal endothelium by minus power anterior chamber intraocular lenses. Refract Corneal Surg 1991; 7:282285 17. Saragoussi Othenin-Girard P, Pouliquen YJ. Ocular damage after implantation of oversized minus power anterior chamber intraocular lenses in myopic phakic eyes: case reports. Refract Corneal Surg 1993; 9:105-109 18. Mimouni F, Colin J, Koffi V, Bonnet P. Damage to the corneal endothelium from anterior chamber intraocular lenses in phakic myopic eyes. Refract Corneal Surg 1991; 7:277-281 19. Alio JL, Ruiz-Moreno JM, Artola A. Retinal detachment as a potential hazard in surgical correction of severe myopia with phakic anterior chamber lenses. Am J Ophthalmol1993; 115:143-148, erratum p 831 20. Fyodorov SN, Zuev VY, Aznabayev BM. Intraocular correction of high myopia with negative posterior chamber lens. Ophthalmosurgery 1991; 3:57-58 21. Assetto V, Benedetti S, Pesando P. Collamer intraocular contact lens to correct myopia. J Cataract Refract Surg 1996; 22:551-556

n,

n,

From the Centre for Advanced Refractive Eye Surgery at the BM! Alexandra Hospital Cheadle, Manchester, United Kingdom. Neither author has a proprietary or financial interest in the intraocular lens described.

J CATARACT REFRACT SURG-VOL 24, MAY 1998