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Contact lens fitting after myopiceratomileusis
Contact Lens Fitting After Myopic Keratomileusis J o h n Gusto*
Introduction Four patients (7 eyes) required contact lenses after undergoing Myopic Keratomileusis (MKM). Gas permeable rind contact lenses were used to correct varying degrees of hyperopia, myopia, and corneal astigmatism. After surgery spherical errors ranged from 2.00 to +4.50 D, corneal astigmatism ranged from -1.25 to -5.50D. The irregular corneal topography encountered in these cases made fitting challenging. Generally, lenses were fitted steeper than K. In all eyes, a lens diameter greater than 9.00ram was needed. This made centration possible, therefore improving vision. All of the eyes were successfully fitted, with sLx of them achieving visual acuities of 6/6, the remaining eye achieved vision of 6/18, which was the best corrected vision preoperatively due to myopic degeneration of the posterior pole. The age of the patients ranged from 3146 years, with four eyes requiring a correction for reading over the contact lenses. This report describes the special problems posed when fitting corneas after keratomileusis and discusses methods to successfully fit these eyes. Refractive keratoplasty, the surreal modification of corneal curvature to correct refractive errors, was first proposed by Jose Barraquer in 1949. Since that time, a variety of procedures have been developed by Barraquer that can correct hyperopia, myopia, and astigmatism. In Myopic Keratomileusis (MKM), a lameltar keratectomy is resected by a microkeratome from the cornea, than frozen, and on a cryolathe carved according to calculations. The lenticule is then thawed and sutured in its original position. The cornea is thus flattened and the myopia reduced. Distinguishing from epikeratopha"tda, in which the lenticule is commercially carved, so that the surgeon will not need to purchase or operate the cryotathe. The microkeratome will resect a circular disc which has beveled borders and parallel faces in the center. The instruments can resect discs of different size and thickness. The initial disc thickness is 0.32mm, with the "Optometrist El-Maghraby Specialist Hospital J eddah, Saudi Arabia
74
disc size being 7ram. Recovery time is from 3.6 months (Barraquer 1981). MI~M Criteria Spherical refractive errors are usually over -6.00 D, however, cases have been performed as low as -4.50 D. With cylindrical refractive errors as high as 4.00 D. Those with irregular corneal astigmatism are unlikely candidates for MKaM. The corneal thickness, or pachymetry measurements must be >0.50ram to minimize interface complications. The age of the candidates are generally over 18 years, but there have been cases reported in children (Ainslie 1975). MKM Postoperative Course Initially an overcorrection of 25 % more than the desired calculations can be expected. A general rule is that, the higher the presurgical refracti'ee error, the higher the postsurgical overcorrection. Moreover, MKM patients are usually hyperopic postsurgically, however, the amount of hyperopia decreases with time. The cylindrical component is often times the same or less than before surgery, with a residual predominantly 'against the rule'. ~h-VlK Complications Perforations, infections, astigmatism, corneal irregularity, interface opacities, and decentration can be possible complications following surgery. Materials and Methods Six months after MKM; refractions, keratometry, and biomicroscopy was performed on all patients prior to contact lens fitting. Initially, PMMA trial lenses were used. The first criteria was to establish centration, foUowed by the best possible fit. Lenses with overall diameters of > 9.00ram were required to cover the suture site. Once centration was achieved, spherical overrefraction was performed, along with testing of visual acuity, followed by cylindrical overrefraction by retinoscopy, also with visual acuity testing. Patients were asked to return for two consecutive weeks for contact lens fitting modifications. By the end of the third session, the appropriate lens was prescribed. Variables for consideration were; best visual acuity at distance and near, best possible fit, and comfort. Upon prescribing, the lens material of choice was the blue Boston 4. Results Six months after MKM, the refractive results are as follows; the spherical components of the 7 eyes ranged from +4.50 to -2.00 D, with the cylindrical components ranging from -1.25 to -5.50 D. In addition, keratometry values ranged from 7.30 to 9.50mm, with 5 eyes having 'against the rule' astigmatism, while the remaining 2 eyes being 'with the rule. Furthermore, upon slit lamp examination, aU patients revealed varying degrees of stromal scarring. In two of the eyes, astigmatic
Transactions BCL~ lntemationa|
Coaferen¢~t988
reductions were performed post MKM, in these eyes small isolated interface opacities were present. All of the eyes required steeper than K fit to maintain centration. Out of the 7 eyes, 5 were fit with standard blue Boston 4 gas permeable contact lenses, while the remaining 2 eyes required bitoric design due to the astigmatic corneas. Of the 7 eyes, 6 received visual acuities of 6 / 6 (20/20), while the remaining eye achieved 6/18 (20/60) at distance. Four of the 7 eyes required reading glasses over the contact lenses. In addition, all complained of light sensitivity and glare at night, as well as in the day. Discussion The initial response from some of the patients after MKM was mixed. Though, all were informed that their eyes were going to improve with time after surgery, some did not seem convinced especially when they were prescribed glasses with plus lenses shortly after surgery. As months passed, they did notice their vision improving. This is why it is best to wait for "6 months before fitting with contact lenses. By this time, the cornea stabilizes, therefore, making contact lens intervention appropriate for the residual corneal irregularity and refractive error. The blue Boston 4 material was the preferred lens of choice due to the DK value (26.3), hardness (118 Rockwell), and the wetting angle (17). The blue tint was selected due to the light transmissibility (above 500 NM 90%) for critical vision. Also the tint provides a softening effect from entering rays of light (Lebow 1985). Regardless of the softening effect from the tint of the lens, patients still complained of glare, especially at night. To remedy daytime problems with glare, polarize sunglasses were prescribed. For nighttime glare, additional myopic spectacles were prescribed to reduce the amount of spherical aberration. This helped some, though, it seems that time and adaptation is the best Rx for this optically-induced error. The MKM patient is particularly challenging due to the central corneal flattening along with interface steepening. Therefore, the desired goal is to fit as flat as possible to minimize vaulting over a depressed central zone, but yet avoid excessive touch at the interface, in conjunction with edge lift, while still maintaining good
Transactions BCLA Internationa| Conference 1988
centration. Consequently, using larger diameter lenses without increasing the optical zone of the lens helped minimize vaulting. Even with these considerations, clearance did exist over the depressed central cornea. In one eye, a piggyback system was tried but failed due to patient intolerance, fortunately, the bitoric design was a success. However, if a special design gas permeable will not centrate then a piggyback may be your last option. Despite the rigors in fitting the lens, the visual response from the patients makes all the effort worthwhile. Out of 7 eyes, 6 achieved acuities of 6/6 (20/20), which was at the minimum a visual acuity line improvement from best corrected vision with spectacles. While one eye achieved 6/18 (20/60), which was the best corrected vision preoperatively, due to myopic degeneration of the posterior pole. Out of the 7 eyes, 4 required reading glasses over contact lenses. The age of these patients was 36 and 4 6 years: Depending on the phoria at near, myopes that use contact lenses may have to accommodate more than with spectacles. Consequently, the pre-presbyopic contact lens wearing myope may need to use a reading correction more readily due to the decrease ability to accommodate (Grosvenor 1982). The freeze MKM developed by Barraquer was a fantastic method to surgically reduce high amounts of myopia. This paper was written to describe the contact lens management for patients undergoing the classical freeze MKM. Since the inception of this paper, Luis Ruiz and Eduardo Viteri streamlined Barraquer's procedure which they termed 'MKM in Situ'. Though this is a fairly recent procedure, the results look very promising in reducing the complications involved with the freeze MKM. In the near future, we will see how this procedure affects postsurgical contact lens management. References Ainslie D (1975), UnilateralMyopia. Soo Amer Oftal Optom 10: 373-381. Barraquer J, SwingerC (1981) Keratophakiaand KeratomiteusisClinicalResults. Ophthal88: 709-715. DabeziesO (1984) CLAO Contact Lenses. 13: 54.1-54.4. Gruneand Stratton, Boston. GrosvenorT (1.982) Primary Care Optomety. 14: 319-384. ProfessionalPress, Chicago. LebowK (1985) The Boston4 Lens. Rev of Optom 122: 65-71.
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Introduction Four patients (7 eyes) required contact lenses after undergoing Myopic Keratomileusis (MKM). Gas permeable rind contact lenses were used to correct varying degrees of hyperopia, myopia, and corneal astigmatism. After surgery spherical errors ranged from 2.00 to +4.50 D, corneal astigmatism ranged from -1.25 to -5.50D. The irregular corneal topography encountered in these cases made fitting challenging. Generally, lenses were fitted steeper than K. In all eyes, a lens diameter greater than 9.00ram was needed. This made centration possible, therefore improving vision. All of the eyes were successfully fitted, with sLx of them achieving visual acuities of 6/6, the remaining eye achieved vision of 6/18, which was the best corrected vision preoperatively due to myopic degeneration of the posterior pole. The age of the patients ranged from 3146 years, with four eyes requiring a correction for reading over the contact lenses. This report describes the special problems posed when fitting corneas after keratomileusis and discusses methods to successfully fit these eyes. Refractive keratoplasty, the surreal modification of corneal curvature to correct refractive errors, was first proposed by Jose Barraquer in 1949. Since that time, a variety of procedures have been developed by Barraquer that can correct hyperopia, myopia, and astigmatism. In Myopic Keratomileusis (MKM), a lameltar keratectomy is resected by a microkeratome from the cornea, than frozen, and on a cryolathe carved according to calculations. The lenticule is then thawed and sutured in its original position. The cornea is thus flattened and the myopia reduced. Distinguishing from epikeratopha"tda, in which the lenticule is commercially carved, so that the surgeon will not need to purchase or operate the cryotathe. The microkeratome will resect a circular disc which has beveled borders and parallel faces in the center. The instruments can resect discs of different size and thickness. The initial disc thickness is 0.32mm, with the "Optometrist El-Maghraby Specialist Hospital J eddah, Saudi Arabia
74
disc size being 7ram. Recovery time is from 3.6 months (Barraquer 1981). MI~M Criteria Spherical refractive errors are usually over -6.00 D, however, cases have been performed as low as -4.50 D. With cylindrical refractive errors as high as 4.00 D. Those with irregular corneal astigmatism are unlikely candidates for MKaM. The corneal thickness, or pachymetry measurements must be >0.50ram to minimize interface complications. The age of the candidates are generally over 18 years, but there have been cases reported in children (Ainslie 1975). MKM Postoperative Course Initially an overcorrection of 25 % more than the desired calculations can be expected. A general rule is that, the higher the presurgical refracti'ee error, the higher the postsurgical overcorrection. Moreover, MKM patients are usually hyperopic postsurgically, however, the amount of hyperopia decreases with time. The cylindrical component is often times the same or less than before surgery, with a residual predominantly 'against the rule'. ~h-VlK Complications Perforations, infections, astigmatism, corneal irregularity, interface opacities, and decentration can be possible complications following surgery. Materials and Methods Six months after MKM; refractions, keratometry, and biomicroscopy was performed on all patients prior to contact lens fitting. Initially, PMMA trial lenses were used. The first criteria was to establish centration, foUowed by the best possible fit. Lenses with overall diameters of > 9.00ram were required to cover the suture site. Once centration was achieved, spherical overrefraction was performed, along with testing of visual acuity, followed by cylindrical overrefraction by retinoscopy, also with visual acuity testing. Patients were asked to return for two consecutive weeks for contact lens fitting modifications. By the end of the third session, the appropriate lens was prescribed. Variables for consideration were; best visual acuity at distance and near, best possible fit, and comfort. Upon prescribing, the lens material of choice was the blue Boston 4. Results Six months after MKM, the refractive results are as follows; the spherical components of the 7 eyes ranged from +4.50 to -2.00 D, with the cylindrical components ranging from -1.25 to -5.50 D. In addition, keratometry values ranged from 7.30 to 9.50mm, with 5 eyes having 'against the rule' astigmatism, while the remaining 2 eyes being 'with the rule. Furthermore, upon slit lamp examination, aU patients revealed varying degrees of stromal scarring. In two of the eyes, astigmatic
Transactions BCL~ lntemationa|
Coaferen¢~t988
reductions were performed post MKM, in these eyes small isolated interface opacities were present. All of the eyes required steeper than K fit to maintain centration. Out of the 7 eyes, 5 were fit with standard blue Boston 4 gas permeable contact lenses, while the remaining 2 eyes required bitoric design due to the astigmatic corneas. Of the 7 eyes, 6 received visual acuities of 6 / 6 (20/20), while the remaining eye achieved 6/18 (20/60) at distance. Four of the 7 eyes required reading glasses over the contact lenses. In addition, all complained of light sensitivity and glare at night, as well as in the day. Discussion The initial response from some of the patients after MKM was mixed. Though, all were informed that their eyes were going to improve with time after surgery, some did not seem convinced especially when they were prescribed glasses with plus lenses shortly after surgery. As months passed, they did notice their vision improving. This is why it is best to wait for "6 months before fitting with contact lenses. By this time, the cornea stabilizes, therefore, making contact lens intervention appropriate for the residual corneal irregularity and refractive error. The blue Boston 4 material was the preferred lens of choice due to the DK value (26.3), hardness (118 Rockwell), and the wetting angle (17). The blue tint was selected due to the light transmissibility (above 500 NM 90%) for critical vision. Also the tint provides a softening effect from entering rays of light (Lebow 1985). Regardless of the softening effect from the tint of the lens, patients still complained of glare, especially at night. To remedy daytime problems with glare, polarize sunglasses were prescribed. For nighttime glare, additional myopic spectacles were prescribed to reduce the amount of spherical aberration. This helped some, though, it seems that time and adaptation is the best Rx for this optically-induced error. The MKM patient is particularly challenging due to the central corneal flattening along with interface steepening. Therefore, the desired goal is to fit as flat as possible to minimize vaulting over a depressed central zone, but yet avoid excessive touch at the interface, in conjunction with edge lift, while still maintaining good
Transactions BCLA Internationa| Conference 1988
centration. Consequently, using larger diameter lenses without increasing the optical zone of the lens helped minimize vaulting. Even with these considerations, clearance did exist over the depressed central cornea. In one eye, a piggyback system was tried but failed due to patient intolerance, fortunately, the bitoric design was a success. However, if a special design gas permeable will not centrate then a piggyback may be your last option. Despite the rigors in fitting the lens, the visual response from the patients makes all the effort worthwhile. Out of 7 eyes, 6 achieved acuities of 6/6 (20/20), which was at the minimum a visual acuity line improvement from best corrected vision with spectacles. While one eye achieved 6/18 (20/60), which was the best corrected vision preoperatively, due to myopic degeneration of the posterior pole. Out of the 7 eyes, 4 required reading glasses over contact lenses. The age of these patients was 36 and 4 6 years: Depending on the phoria at near, myopes that use contact lenses may have to accommodate more than with spectacles. Consequently, the pre-presbyopic contact lens wearing myope may need to use a reading correction more readily due to the decrease ability to accommodate (Grosvenor 1982). The freeze MKM developed by Barraquer was a fantastic method to surgically reduce high amounts of myopia. This paper was written to describe the contact lens management for patients undergoing the classical freeze MKM. Since the inception of this paper, Luis Ruiz and Eduardo Viteri streamlined Barraquer's procedure which they termed 'MKM in Situ'. Though this is a fairly recent procedure, the results look very promising in reducing the complications involved with the freeze MKM. In the near future, we will see how this procedure affects postsurgical contact lens management. References Ainslie D (1975), UnilateralMyopia. Soo Amer Oftal Optom 10: 373-381. Barraquer J, SwingerC (1981) Keratophakiaand KeratomiteusisClinicalResults. Ophthal88: 709-715. DabeziesO (1984) CLAO Contact Lenses. 13: 54.1-54.4. Gruneand Stratton, Boston. GrosvenorT (1.982) Primary Care Optomety. 14: 319-384. ProfessionalPress, Chicago. LebowK (1985) The Boston4 Lens. Rev of Optom 122: 65-71.
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