- Email: [email protected]
May consultation #4
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CONSULTATION SECTION
it would be hyperopic PRK, would not touch the central cornea. First, PTK laser pulses with a masking agent (balanced salt solution) would be applied to remove the central scar and smooth the surface. Next, I would perform PRK to correct most of the hyperopic anisometropia. I would treat the entire preoperative hyperopia. More hyperopic PRK could be attempted depending on the depth of the second PTK. The amount of PTKinduced hyperopia depends on many factors, such as the laser platform (broad beam versus flying spot), ablation profile (size, asphericity, blend zone) and, most important, the amount of masking agent used. Because of these factors, the prediction of PTK-induced hyperopia would be based more on an individualized surgeon’s nomogram. At the end of surgery, I would apply MMC 0.02% for 45 seconds to decrease the risk for haze recurrence. Postoperatively, I would fit a bandage contact lens until complete reepithelialization. I would prescribe profuse lubrication to optimize the ocular surface and a slow steroid taper to prevent haze formation. Mohamed Abou Shousha, MD Miami, Florida, USA
- The main issue in this case is irregular astigmatism related to anterior stromal scarring. The slitlamp photograph shows a well-circumscribed central zone of scarring (approximately 6.0 mm) consistent with a broad-beam excimer laser used for the PTK. The level of opacification is not severe centrally, indicating that the irregularity of the anterior corneal surface (Figure 2), not opacification, is the main cause of the poor CDVA. Therefore, RGP contact lens overrefraction should be used to determine the potential visual acuity. We must presume that MMC was not used during the initial PTK because it was not mentioned. We also do not know the ablation depth, although the difference in central corneal thickness between the treated eye and untreated eye is 48 mm, suggesting a 50 mm ablation. The hyperopic refraction, albeit with a poor endpoint, is consistent with a myopic (central) ablation and the anterior stromal scarring. In general, epithelial debridement with diamond burr polishing is preferable to PTK in patients with recurrent erosion syndrome in whom a refractive error is not being corrected. Alternatively, when PTK is used in these patients, only about 5 mm of tissue has to be ablated, significantly less than what was apparently removed in this case. Sridhar et al.1 report a 35.7% incidence of mild haze after 5 mm PTK in patients with anterior basement membrane dystrophy.
The first and least invasive option is to fit an RGP lens. Assuming this is unacceptable, the next option is to perform another excimer procedure, this time with MMC 0.02% for 30 to 45 seconds, to improve the anterior corneal curvature. The slitlamp photograph shows that most haze is in the paracentral region, leaving the central cornea clear. However, the corneal topography shows irregularity extending into the central cornea. A second topography taken after epithelial removal and just before combined PTK–PRK would be useful in determining how to program the laser.2 Anterior segment OCT can be used to estimate the depth of the anterior stromal scarring for planning the ablation depth.3 I would remove the epithelium using 20% ethanol and apply a masking agent (eg, 50:50 mixture of high- and low-viscosity carboxymethylcellulose) during the ablation if the area of haze appears to be irregular and involves the central cornea. We do not know the patient’s pre-PTK refraction. Assuming it was similar to that in the fellow eye (approximately 0.50 D), a 50 mm ablation would have left a spherical equivalent (SE) of approximately C3.50 D (Munnerlyn formula with 6.0 mm optical zone: 50 3/62 Z 4.17 0.50 Z 3.67 D). The refraction given has an SE of C3.75 D, which is consistent with this calculation. Accordingly, a programmed hyperopic PRK–PTK of 3.00 to 4.00 D (depending on how much masking is required) at the appropriate optical zone (looks like 6.0 mm) should effectively treat the refractive error and smooth the corneal contour. D. Rex Hamilton, MD, MS Los Angeles, California, USA
REFERENCES 1. Sridhar MS, Rapuano CJ, Cosar CB, Cohen EJ, Laibson PR. Phototherapeutic keratectomy versus diamond burr polishing of Bowman’s membrane in the treatment of recurrent corneal erosions associated with anterior basement membrane dystrophy. Ophthalmology 2002; 109:674–679 2. Gatinel D, Racine L, Hoang-Xuan T. Contribution of the corneal epithelium to anterior corneal topography in patients having myopic photorefractive keratectomy. J Cataract Refract Surg 2007; 33:1860–1865 3. Ma JJK, Tseng SS, Yarascavitch BA. Anterior segment optical coherence tomography for transepithelial phototherapeutic keratectomy in central corneal stromal scarring. Cornea 2009; 28: 927–929
- In this case, PTK in the right eye to treat idiopathic recurrent corneal erosions resulted in significant anterior stromal haze and a 3.75 D hyperopic shift. The patient has poor quality of vision, with a CDVA of 20/100, and topography shows significant flattening
J CATARACT REFRACT SURG - VOL 36, MAY 2010
CONSULTATION SECTION
in the central cornea. The most important issues to address are the reason for the induced hyperopia and how to treat the loss of CDVA. The thickness of Bowman layer is approximately 12 mm; a partial ablation depth between 3 mm and 10 mm is sufficient to achieve healthy migration of the surface epithelium and formation of a new basement membrane. This depth of ablation has no or a minor effect on the refractive error.1 The postoperative pachymetric difference between the 2 eyes in this case is 48 mm, in excess of what is necessary to ablate Bowman membrane. In addition, the circular pattern of the anterior stromal haze corresponds to an ablation width of 6.0 to 7.0 mm. These findings show that during treatment, all ablation was performed directly in the center of the cornea. Creating a wider ablation, performing some ablation in the peripheral cornea, and using an integrated slitlamp on the laser could have avoided the overablation. The first treatment option in this patient is an RGP contact lens trial for visual rehabilitation. If visual acuity does not improve with the lenses, another excimer laser treatment would be required. The major question is when to correct the residual refractive error. Some prefer to correct the error and the stromal haze during the same session. However, performing PTK alone can significantly improve the refractive error in patients with stromal haze and a refractive shift. I would elect to remove the epithelium with ethanol and perform PTK with MMC 0.02% (0.2 mg/mL) for 2 minutes. The main haze-inhibiting effect of MMC is at the level of blocking keratocyte transformation into myofibroblasts. Mitomycin-C is less effective in producing apoptosis of preexisting myofibroblasts, thereby requiring a longer exposure for therapeutic purposes.2 After the refraction stabilizes, the patient can have another surface ablation for the correction of hyperopia, again with the use of adjuvant MMC. If this approach fails, the patient may be a candidate for femtosecond laser–assisted anterior lamellar keratoplasty for visual rehabilitation.3 Volkan Hu¨rmeric¸, MD Miami, Florida, USA Ankara, Turkey
REFERENCES 1. Rashad KM, Hussein HA, El-Samadouny MA, El-Baha S, Farouk H. Phototherapeutic keratectomy in patients with recurrent corneal epithelial erosions. J Refract Surg 2001; 17:511–518 2. Netto MV, Mohan RR, Sinha S, Sharma A, Gupta PC, Wilson SE. Effect of prophylactic and therapeutic mitomycin C on corneal
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apoptosis, cellular proliferation, haze, and long-term keratocyte density in rabbits. J Refract Surg 2006; 22:562–574 3. Yoo SH, Kymionis GD, Koreishi A, Ide T, Goldman D, Karp CL, O’Brien TP, Culbertson WW, Alfonso EC. Femtosecond laser-assisted sutureless anterior lamellar keratoplasty. Ophthalmology 2008; 115:1303–1307
- This patient with recurrent erosion syndrome and a history of anterior stromal puncture followed by subsequent PTK presents with 20/300 UDVA, 3C central corneal haze, and a hyperopic refraction. Haze rarely develops after PTK for recurrent erosion syndrome because the ablations are superficial (5 to 7 mm) unless reepithelialization after the treatment was extended because of factors such as dry eye. The refraction and pachymetry before PTK are not given. Assuming they were the same as in the fellow eye, it appears that the ablation was 40 to 50 mm, which is consistent with a postoperative 4.00 diopter (D) hyperopic shift in the right eye and corneal topography findings of a well-centered ablation. Review of the patient’s treatment records would be helpful. Because the patient had previous anterior stromal puncture and subepithelial corneal scarring, activated keratocytes were likely present, increasing the risk for postoperative haze. To manage this case, I would discuss the situation with the patient and emphasize that haze reduction rather than the refractive outcome would be the goal. Also, I would emphasize that the corneal haze may recur. I would optimize the anterior ocular surface with lubricants, temporary plugs, and topical cyclosporine (if required) before treatment to ensure rapid reepithelialization of the cornea. Next, I would perform a superficial keratectomy to remove the central 9.0 mm of corneal epithelium and irregularly elevated scar tissue. After superficial keratectomy, I would treat 50% to 65% of the refraction and apply MMC 0.02% for 60 seconds. The 60-second application is based on a literature review (not published) I performed last year of MMC treatment in eyes with pathologic corneal haze. In many cases with pathologic corneal haze after excimer laser treatment there is corneal flattening, resulting in a hyperopic shift; however, the data given here suggest that the patient received a deep PTK ablation. I never treat the full correction; my limit is 50% to 65% of the refraction because scar removal can greatly affect the refractive outcome. Another reason for the reduced treatment is the MMC application; however, the amount of treatment reduction varies by surgeon. At the end of the procedure, I would place an extended-wear contact lens to facilitate corneal epithelialization; the contact lens would be worn until the
J CATARACT REFRACT SURG - VOL 36, MAY 2010
CONSULTATION SECTION
it would be hyperopic PRK, would not touch the central cornea. First, PTK laser pulses with a masking agent (balanced salt solution) would be applied to remove the central scar and smooth the surface. Next, I would perform PRK to correct most of the hyperopic anisometropia. I would treat the entire preoperative hyperopia. More hyperopic PRK could be attempted depending on the depth of the second PTK. The amount of PTKinduced hyperopia depends on many factors, such as the laser platform (broad beam versus flying spot), ablation profile (size, asphericity, blend zone) and, most important, the amount of masking agent used. Because of these factors, the prediction of PTK-induced hyperopia would be based more on an individualized surgeon’s nomogram. At the end of surgery, I would apply MMC 0.02% for 45 seconds to decrease the risk for haze recurrence. Postoperatively, I would fit a bandage contact lens until complete reepithelialization. I would prescribe profuse lubrication to optimize the ocular surface and a slow steroid taper to prevent haze formation. Mohamed Abou Shousha, MD Miami, Florida, USA
- The main issue in this case is irregular astigmatism related to anterior stromal scarring. The slitlamp photograph shows a well-circumscribed central zone of scarring (approximately 6.0 mm) consistent with a broad-beam excimer laser used for the PTK. The level of opacification is not severe centrally, indicating that the irregularity of the anterior corneal surface (Figure 2), not opacification, is the main cause of the poor CDVA. Therefore, RGP contact lens overrefraction should be used to determine the potential visual acuity. We must presume that MMC was not used during the initial PTK because it was not mentioned. We also do not know the ablation depth, although the difference in central corneal thickness between the treated eye and untreated eye is 48 mm, suggesting a 50 mm ablation. The hyperopic refraction, albeit with a poor endpoint, is consistent with a myopic (central) ablation and the anterior stromal scarring. In general, epithelial debridement with diamond burr polishing is preferable to PTK in patients with recurrent erosion syndrome in whom a refractive error is not being corrected. Alternatively, when PTK is used in these patients, only about 5 mm of tissue has to be ablated, significantly less than what was apparently removed in this case. Sridhar et al.1 report a 35.7% incidence of mild haze after 5 mm PTK in patients with anterior basement membrane dystrophy.
The first and least invasive option is to fit an RGP lens. Assuming this is unacceptable, the next option is to perform another excimer procedure, this time with MMC 0.02% for 30 to 45 seconds, to improve the anterior corneal curvature. The slitlamp photograph shows that most haze is in the paracentral region, leaving the central cornea clear. However, the corneal topography shows irregularity extending into the central cornea. A second topography taken after epithelial removal and just before combined PTK–PRK would be useful in determining how to program the laser.2 Anterior segment OCT can be used to estimate the depth of the anterior stromal scarring for planning the ablation depth.3 I would remove the epithelium using 20% ethanol and apply a masking agent (eg, 50:50 mixture of high- and low-viscosity carboxymethylcellulose) during the ablation if the area of haze appears to be irregular and involves the central cornea. We do not know the patient’s pre-PTK refraction. Assuming it was similar to that in the fellow eye (approximately 0.50 D), a 50 mm ablation would have left a spherical equivalent (SE) of approximately C3.50 D (Munnerlyn formula with 6.0 mm optical zone: 50 3/62 Z 4.17 0.50 Z 3.67 D). The refraction given has an SE of C3.75 D, which is consistent with this calculation. Accordingly, a programmed hyperopic PRK–PTK of 3.00 to 4.00 D (depending on how much masking is required) at the appropriate optical zone (looks like 6.0 mm) should effectively treat the refractive error and smooth the corneal contour. D. Rex Hamilton, MD, MS Los Angeles, California, USA
REFERENCES 1. Sridhar MS, Rapuano CJ, Cosar CB, Cohen EJ, Laibson PR. Phototherapeutic keratectomy versus diamond burr polishing of Bowman’s membrane in the treatment of recurrent corneal erosions associated with anterior basement membrane dystrophy. Ophthalmology 2002; 109:674–679 2. Gatinel D, Racine L, Hoang-Xuan T. Contribution of the corneal epithelium to anterior corneal topography in patients having myopic photorefractive keratectomy. J Cataract Refract Surg 2007; 33:1860–1865 3. Ma JJK, Tseng SS, Yarascavitch BA. Anterior segment optical coherence tomography for transepithelial phototherapeutic keratectomy in central corneal stromal scarring. Cornea 2009; 28: 927–929
- In this case, PTK in the right eye to treat idiopathic recurrent corneal erosions resulted in significant anterior stromal haze and a 3.75 D hyperopic shift. The patient has poor quality of vision, with a CDVA of 20/100, and topography shows significant flattening
J CATARACT REFRACT SURG - VOL 36, MAY 2010
CONSULTATION SECTION
in the central cornea. The most important issues to address are the reason for the induced hyperopia and how to treat the loss of CDVA. The thickness of Bowman layer is approximately 12 mm; a partial ablation depth between 3 mm and 10 mm is sufficient to achieve healthy migration of the surface epithelium and formation of a new basement membrane. This depth of ablation has no or a minor effect on the refractive error.1 The postoperative pachymetric difference between the 2 eyes in this case is 48 mm, in excess of what is necessary to ablate Bowman membrane. In addition, the circular pattern of the anterior stromal haze corresponds to an ablation width of 6.0 to 7.0 mm. These findings show that during treatment, all ablation was performed directly in the center of the cornea. Creating a wider ablation, performing some ablation in the peripheral cornea, and using an integrated slitlamp on the laser could have avoided the overablation. The first treatment option in this patient is an RGP contact lens trial for visual rehabilitation. If visual acuity does not improve with the lenses, another excimer laser treatment would be required. The major question is when to correct the residual refractive error. Some prefer to correct the error and the stromal haze during the same session. However, performing PTK alone can significantly improve the refractive error in patients with stromal haze and a refractive shift. I would elect to remove the epithelium with ethanol and perform PTK with MMC 0.02% (0.2 mg/mL) for 2 minutes. The main haze-inhibiting effect of MMC is at the level of blocking keratocyte transformation into myofibroblasts. Mitomycin-C is less effective in producing apoptosis of preexisting myofibroblasts, thereby requiring a longer exposure for therapeutic purposes.2 After the refraction stabilizes, the patient can have another surface ablation for the correction of hyperopia, again with the use of adjuvant MMC. If this approach fails, the patient may be a candidate for femtosecond laser–assisted anterior lamellar keratoplasty for visual rehabilitation.3 Volkan Hu¨rmeric¸, MD Miami, Florida, USA Ankara, Turkey
REFERENCES 1. Rashad KM, Hussein HA, El-Samadouny MA, El-Baha S, Farouk H. Phototherapeutic keratectomy in patients with recurrent corneal epithelial erosions. J Refract Surg 2001; 17:511–518 2. Netto MV, Mohan RR, Sinha S, Sharma A, Gupta PC, Wilson SE. Effect of prophylactic and therapeutic mitomycin C on corneal
869
apoptosis, cellular proliferation, haze, and long-term keratocyte density in rabbits. J Refract Surg 2006; 22:562–574 3. Yoo SH, Kymionis GD, Koreishi A, Ide T, Goldman D, Karp CL, O’Brien TP, Culbertson WW, Alfonso EC. Femtosecond laser-assisted sutureless anterior lamellar keratoplasty. Ophthalmology 2008; 115:1303–1307
- This patient with recurrent erosion syndrome and a history of anterior stromal puncture followed by subsequent PTK presents with 20/300 UDVA, 3C central corneal haze, and a hyperopic refraction. Haze rarely develops after PTK for recurrent erosion syndrome because the ablations are superficial (5 to 7 mm) unless reepithelialization after the treatment was extended because of factors such as dry eye. The refraction and pachymetry before PTK are not given. Assuming they were the same as in the fellow eye, it appears that the ablation was 40 to 50 mm, which is consistent with a postoperative 4.00 diopter (D) hyperopic shift in the right eye and corneal topography findings of a well-centered ablation. Review of the patient’s treatment records would be helpful. Because the patient had previous anterior stromal puncture and subepithelial corneal scarring, activated keratocytes were likely present, increasing the risk for postoperative haze. To manage this case, I would discuss the situation with the patient and emphasize that haze reduction rather than the refractive outcome would be the goal. Also, I would emphasize that the corneal haze may recur. I would optimize the anterior ocular surface with lubricants, temporary plugs, and topical cyclosporine (if required) before treatment to ensure rapid reepithelialization of the cornea. Next, I would perform a superficial keratectomy to remove the central 9.0 mm of corneal epithelium and irregularly elevated scar tissue. After superficial keratectomy, I would treat 50% to 65% of the refraction and apply MMC 0.02% for 60 seconds. The 60-second application is based on a literature review (not published) I performed last year of MMC treatment in eyes with pathologic corneal haze. In many cases with pathologic corneal haze after excimer laser treatment there is corneal flattening, resulting in a hyperopic shift; however, the data given here suggest that the patient received a deep PTK ablation. I never treat the full correction; my limit is 50% to 65% of the refraction because scar removal can greatly affect the refractive outcome. Another reason for the reduced treatment is the MMC application; however, the amount of treatment reduction varies by surgeon. At the end of the procedure, I would place an extended-wear contact lens to facilitate corneal epithelialization; the contact lens would be worn until the
J CATARACT REFRACT SURG - VOL 36, MAY 2010