Post-RK/AK Correction and an Amblyopic Eye

A 36-year-old female presents with a request for intervention. She formerly wore contact lenses. With age, she has become contact lens intolerant, however, and her wearing times have decreased from between 12 and 14 hours per day to 2 hours per day. Medical management of her dry eye syndrome with artificial tears, nutritional supplementation, Restasis (Allergan, Inc., Irvine, CA), and punctal occlusion has been unsuccessful.

The patient underwent bilateral automated lamellar keratoplasty (ALK) in July 1994. Her preoperative refractions were -11.5 +4.5 X 110 for 20/50 BCVA OD and -10.50 +6 X 95 for 20/25 BCVA OS. Her right eye has always been amblyopic. The patient underwent treatment of her right eye first and proceeded with surgery on her left eye several months later, once she felt comfortable with the surgical result in her amblyopic eye. The patient later underwent RK/astigmatic keratotomy (AK) enhancements in both eyes after her residual refractive error stabilized.

Currently, she has UCVAs of 20/200 OD and 20/40 OS. With toric contact lenses, she sees 20/50 OD and 20/25 OS. She is wearing soft spherical lenses with a -5.75-D correction on her right eye and a -2.75-D correction for her left. She cannot tolerate other types of contact lenses, despite consultations with four different contact lens specialists who routinely work with postrefractive surgery patients. Spectacle correction is difficult secondary to anisometropia-related subjective complaints.

The patient's manifest refraction is -6.75 +2.25 X 179 OD and -4 +2.00 X 175 OS. Her pachymetry measures 491µm OD and 510µm OS. Intraoperative stromal pachymetry at the time of the original ALK was not measured. Her examination is remarkable for several incisional epithelial cysts/plugs; stable epithelial ingrowth of < 1.5mm in diameter is observable at the peak of the 2-o'clock incision in her left eye. Figures 1 and 2 show imaging with the Magellan Mapper Corneal Topographer (Nidek Co., Ltd., Gamagori, Japan; distributed in the US by Nidek Technologies America, Greensboro, NC). Consecutive wavefront maps have not been reproducible by currently available technology, and Orbscan topographic maps (Bausch & Lomb, Rochester, NY) are not available for this particular patient.

The patient comes to your office in search of potential options for intervention at this time.

Stephen F. Brint, MD
In this case, the safest solution is obviously spectacles. The patient's UCVA in her dominant left eye is 20/40, and she is probably able to function during the day without too much difficulty. The patient could wear spectacles at night for driving. If she truly desires additional refractive surgery, the only option I would consider would be conventional PRK, both because wavefront readings are unobtainable, and because her extremely high level of spherical aberration would probably lead to overcorrection with current technology. I would operate on one eye at a time, starting with the patient's left eye, which has better (20/25) visual potential. In my hands, PRK over RK and previous LASIK (I have no experience with ALK, but it should behave like LASIK) has been successful with a flying-spot laser and has not produced haze for low levels of correction in cases such as this one. If desired, her right eye could undergo treatment 1 or more months after the first procedure.

Lee T. Nordan, MD
This patient's contact lens intolerance and anisometropia need to be resolved. I would perform bilateral PRK/AK with mitomycin C (MMC) 0.02% applied for

2 minutes. The patient would wear a bandage soft contact lens with steroid and antibiotic coverage for 4 days postoperatively. During PRK, I would gently remove the epithelium by hand with a crescent-shaped blade. This technique ensures that different thicknesses of epithelium are removed down to Bowman's membrane. Removing epithelium by laser scraping would also certainly be acceptable. Lifting the previous LASIK flaps is inadvisable in cases of prior RK and AK as well as when the quality of the previous flaps is unknown.

The surgical goal of the spherical component of the refraction entered into the laser's computer should be reduced by approximately 25%, because cases such as this one tend toward overcorrection. PRK for this level of myopia would offer the added benefit of smoothing out any mild irregular corneal astigmatism that may exist, thereby improving the patient's quality of vision.

The case presentation demonstrates that diagnostic studies of the corneal surface are often less accurate or meaningful than expected due to previous RK/AK and other keratorefractive procedures. An evaluation of the entire clinical picture is therefore necessary.

J. James Rowsey, MD
This patient's corneal astigmatism has reversed 90º from the preoperative steep meridian at 90º to steepness at 180º in both eyes. Such a shift is more often associated with RK or AK wound dehiscence in the vertical meridian, because LASIK reversal of 6.75D in the right eye and 8.00D in the left eye would be unusual. This type of ectasia is frequently associated with incisional epithelial ingrowth such as is seen in this case.

The intrastromal epithelium in an RK incision at the 2-o'clock position in the patient's left eye limits the surgical options. This type of epithelium—dubbed intrastromal epithelial accretion by Richard Green, MD, of Johns Hopkins University—destabilizes the cornea and predisposes the eye to continued ectasia or flattening of the cornea in the axis of the incision. The epithelium remains viable and continually digests the surrounding stromal collagen. Diffuse lamellar epithelial ingrowth is also likely after a second LASIK cut or flap lift. The surface regularity index does not suggest that attention to this epithelial ingrowth is required before surface ablation.

If marked corneal irregularity is visible on the corneal topographic ring images, then the offending RK incision should be cleared of all epithelium and sutured to create a stable surface. This RK repair will be difficult if corneal stromal tissue has been lost due to the epithelial ingrowth, and the procedure should not be undertaken in the eye that the patient prefers because of the long recovery period required for visual stabilization.

The patient's right cornea demonstrates nonorthogonal astigmatism, with the flat axis at 270º and 60º. A steep cornea is visible at the 4-o'clock position. I would recommend making the cornea at this position flatter and, consequently, symmetrical through a limbal-relaxing incision at the 4-o'clock position in the patient's potentially 20/20 eye before proceeding with astigmatic PRK. My preference would be to perform astigmatic PRK with alcohol removal of the epithelium to avoid disturbing the RK incisions, as can occur with mechanical epithelial debridement. Astigmatic PRK for the full refractive error would be safe due to the residual corneal thickness. I would use MMC 0.25 mg/mL on the astigmatic PRK bed for 2 minutes to reduce subsequent scarring.

Stephen G. Slade, MD, FACS
This case is truly diabolical. Anisometropia makes it difficult for the patient to wear spectacles, but surgical options are limited. Contact lenses are almost ruled out by the patient's dry eyes and the failed fitting efforts of four experts. Previous RK and epithelial ingrowth make lifting the flap far from simple, and further incisional surgery is practically contraindicated due to the poor healing of the first RK procedure.

I almost always prefer to lift or even recut a lamellar flap for retreatments, but this case would force me to consider surface ablation. Because the one problem with this surgical modality is haze, I would use MMC. I would treat the patient's amblyopic eye first, wait to see the early surgical result, and then treat the second eye accordingly. I think a scanning laser would provide the smoothest possible ablation in this case.

Section editor Karl G. Stonecipher, MD, is Director of Refractive Surgery at Southeastern Eye Center in Greensboro, North Carolina. Dr. Stonecipher may be reached at (800) 632-0428; stonenc@aol.com.
Stephen F. Brint, MD, is Associate Clinical Professor of Ophthalmology at Tulane University School of Medicine in New Orleans. He states that he holds no financial interest in the products or companies mentioned herein. Dr. Brint may be reached at (504) 888-2020; brintmd@aol.com.
Lee T. Nordan, MD, is a technology consultant for Vision Membrane Technologies, Inc. He states that he holds no financial interest in the products or companies mentioned herein. Dr. Nordan may be reached at (760) 431-1846; laserltn@aol.com.
J. James Rowsey, MD, is Director of Corneal Services at St. Luke's Cataract & Laser Institute in Tarpon Springs, Florida. He states that he holds no financial interest in the products or companies mentioned herein. Dr. Rowsey may be reached at (727) 938-2020 ext. 2262; jrowsey243@aol.com.
Stephen G. Slade, MD, FACS, is in private practice in Houston. He states that he holds no financial interest in the products or companies mentioned herein. Dr. Slade may be reached at (713) 626-5544; sgs@visiontexas.com.