Radial Keratotomy Complicates Cataract Surgery: Nick Wolf, OD, FSLS

Background

A 68 year-old Caucasian male presented for a medically necessary contact lens consultation. He had radial keratotomy performed in Phoenix around 1991 followed by at least one retreatment on both eyes. He was recently evaluated for a decrease in his vision by a local cataract surgeon. A review of the referring physician’s notes revealed that the patient was initially best corrected to 20/50 in the right eye and 20/40 in the left eye with 1+ nuclear sclerotic and 1+ cortical cataracts in both eyes. It was presumed that the cataracts were responsible for the reduction in vision and cataract extraction was performed on the right eye only. After the surgery, he was very unhappy with his vision and best corrected to 20/30 in the right eye. He also noted substantially more visual fluctuation in that right eye, and this was consistent with variable serial refraction within a single day. The patient was warned by the cataract surgeon that his history of extensive radial keratotomy might complicate intraocular lens selection or result in vision changes after the surgery. The patient, however, was under the impression that he would be less reliant on glasses after the surgery, but now feels his vision is much worse and even more unstable. His goal of visiting us was to understand what his contact lens options are, and, if possible, achieve improved, more stable vision without additional surgeries. This case report will examine the potential adverse ocular health and refractive complications of radial keratotomy, as well as showcase one such patient and how his visual sequalae of radial keratotomy were ameliorated with scleral contact lenses.

Test Procedures, Fitting/Refitting, Design, and Ordering

Visit #1: Initial Visit

Unaided Distance Visual Acuities

OD: 20/80
OS: 20/100

Manifest Refraction

OD: +0.75 -3.50 x 083 (20/30-2)
OS: +1.75 -3.00 x 095 (20/40-2)

Pupils, ocular motility, confrontation fields, and ocular alignment were normal. Intraocular pressure was obtained at 4:00 pm and measured 10 mmHg in both eyes with iCare^® tonometry.

Corneal Topography

Corneal topography was performed with the Medmont^™ E300 topographer. The results (Figures 1 and 2) revealed irregular, central astigmatism consistent with his radial keratotomy. This was present in both eyes, but more severe in the right eye than the left. Both corneas showed a large, very flat cornea cap with flattest keratometry readings of 35.25 and 35.70 in the right and left eye, respectively. There was some inferior steepening in both eyes (OD>OS) suggesting mild keratoectasia. All built in screening values for ectasia present in the Medmont software was flagged as abnormal. Via topography, the HVID (horizontal visible iris diameter) was measured at 12.1 mm in the right eye and 12.3 mm in the left eye. Testing was reliable and of good quality.

Pachymetry Mapping

Pachymetry mapping with anterior segment optical coherence tomography or AS-OCT (iVue^® by Optovue™) was also ordered and performed (Figures 3 and 4). The pachymetry map shows thin central corneal thickness, as well as, thinning inferiorly in both eyes consistent with the areas of refractive keratoectasia seen via corneal topography. The baseline pachymetry map also allows us to monitor subtle, hypoxia-related edema from scleral lens wear and to make fitting revisions if needed.

Anterior and Posterior Segment Evaluation

Anterior segment evaluation showed mild blepharitis and moderate conjunctivochalasis in both eyes. Both corneas showed extensive surgical scarring with scarring from the radial incisions extending into the pupil under photopic illumination. The right eye had 12 cut radial keratotomy, as well as, six different astigmatic keratotomy scars spaced between the radial scars, along with surgical stab incisions from the cataract extraction. The left eye had 11 cut radial keratotomy, along with five separate astigmatic keratotomy scars placed in a similar fashion as the right eye.

The patient was not dilated at this visit as he was recently dilated by his ophthalmologist. However, undilated evaluation showed a well-positioned intraocular lens in the right eye and a 1+ nuclear sclerotic cataract in the left eye. Optic nerves were healthy and well perfused with a cup to disk ratio of 0.4 in each eye. The macula in both eyes looked normal with slit lamp and OCT testing.

Given the normal macula, optic nerve, and well positioned lens implant in the right eye, it was clear that the corneas were the likely cause for the reduced vision. Therefore, this patient was diagnosed with mild post-refractive keratoectasia and visual disturbances secondary to radial keratotomy.

Scleral Lens Fitting

Diagnostic Lens Selection

Given the rather extreme hyperopic fluctuations, the patient was not interested in having multiple pairs of glasses to wear throughout the day. We discussed further surgical intervention, including cataract surgery on his left eye, and/or corneal cross linking to help with stabilizing the cornea. However, given his recent experience with cataract extraction in his right eye and the lack of FDA approval for corneal cross linking (at the time), he preferred to investigate his contact lens options. All lens options where discussed, including specialty soft lenses, small diameter hard lenses, hybrid contact lenses, as well as semi-scleral and full scleral contact lenses. He had worn small diameter hard contact lenses many years ago and opted for a hard contact lens to maximize vision and decrease his visual fluctuations. However, with the significant level of central flattening and inferior steepening, we recommended a mini scleral contact lens as his best option.

We wanted a true oblate design to mirror the corneal topography, so we fit the Zenlens™ scleral contact lens by Alden Optical^©. A 17mm lens was deemed necessary given the large HVID. The starting sagittal depth was selected based on the Medmont™ Studio calculated sagittal depth from the composite testing at a chord of 17 mm with an additional 400 µm added for clearance.

Diagnostic Lenses: Zenlens

OD: Oblate Design, BC 9.7, Sag. Depth 4800 µm, Diameter 17.0 mm, Power: -2.00, Standard Landing Zone, Standard Peripheral Curve

OS: Oblate Design, BC 9.1, Sag. Depth 5100 µm, Diameter 17.0 mm, Power: -2.00, Standard Landing Zone, Standard Peripheral Curve

The patient was fairly apprehensive about the large scleral lenses. Therefore, one drop of anesthetic was administered to facilitate initial application. After 5-10 minutes of settling, the lenses were evaluated for fit and over-refraction utilizing slit lamp and AS-OCT (Figures 5-8).

OD: This diagnostic lens showed good centration and minimal movement. The landing cleared the limbus as shown on AS-OCT and analyzing the sodium fluorescein pattern with a wratten filter at the slit lamp. There was some mild compression in the nasal and temporal quadrants, but this was deemed acceptable. Initial sagittal depth was 85 µm centrally with no cornea touch over the inferior mid-peripheral steepening. Sphero-cylinder over-refraction was +6.50 -0.75 x100 with acuity of 20/25-. The actual initial lens ordered for the right eye factored in the spherical over-refraction, as well as, increased the central sagittal depth to the ideal 250-300 µm range to allow for scleral lens settling.

OS: This diagnostic lens also exhibited proper centration and movement. Proper limbal clearance was shown with OCT and slit lamp evaluation. Initial sagittal depth was 302 µm centrally, which was deemed an acceptable starting depth; and no corneal touch was noted inferiorly in the left eye. Sphero-cylinder over-refraction was +5.25 DS with best corrected visual acuity of 20/20. The initial lens ordered for the left eye simply corrected for the over-refraction as the initial starting central sagittal depth was appropriate with the diagnostic lens.

First Lens Order: Zenlens™ Scleral Lens – Boston XO2™

OD: Oblate Design, BC 9.7, Sag. Depth 4970 µm, Diameter 17.0 mm, Power: +4.75, Standard Landing Zone, Standard Peripheral Curve

OS: Oblate Design, BC 9.1, Sag. Depth 5100 µm, Diameter 17.0 mm, Power: +3.50, Standard Landing Zone, Standard Peripheral Curve

Patient Consultation and Education

Visit #2: Dispense, Initial Evaluation, and Training

The patient returned in two weeks for dispensing. At this visit, he was again anesthetized with topical anesthetic for a more comfortable initial experience and a staff member used inhalation solution with sodium fluorescein for initial application of the lenses. The initially dispensed lenses were allowed to sit for 15 minutes before the evaluation was performed.

Under slit lamp, the lenses exhibited proper movement and centration. Fluorescein evaluation with a wratten filter showed full clearance and limbus vaulting. Perfect scleral apposition and landing was observed in the left eye but the right eye still showed nasal and temporal compression. Central sagittal depth was taken with AS-OCT and measured 270 µm in the right eye and 295 µm in the left eye. Initial visual acuity with his lenses was 20/50 in the right eye and 20/25 in the left eye. Over-refraction on the right scleral lens was -0.25 -1.25 x 135 with best corrected vision of 20/30 and +0.25 DS with a best corrected vision of 20/20 in the left eye. Overall this fit was deemed acceptable; however, the patient was educated that the compression and astigmatic over refractive in the right eye would likely need addressed at follow-up.

Application, Removal, and Care Education

The patient was initially apprehensive but noted immediate improvement in the vision especially in his left eye. He was educated on the application, removal, and care of his scleral contact lenses. Clear Care^® hydrogen peroxide-based cleaning solution was recommended for daily cleaning as well as an enzymatic cleaner for as needed use. For lens filling he was prescribed 0.9% NaCl inhalation solution (Addipak^®) for off-label use. In addition to samples of these solutions, the patient was also supplied with a classic DMV™ for application, a 45 degree DMV™ for removal, detailed written instructions, as well as our after-hours contact information. He was also instructed to purchase over-the-counter reading glasses for his near task needs. He left the office wearing his new scleral lenses and was scheduled for a two-week follow-up.

Follow-up Care and Final Outcome

Visit #3: Two Week Follow-Up

The patient returned to our office and was very pleased with the vision in both eyes, but the comfort of the lens in the right eye was not acceptable. He noticed his right eye would often get red, even more so when he removed his lenses. He was still able to get 10 hours of wear time out of his lenses; however, the redness was bothersome enough to schedule an earlier evaluation. He felt very comfortable with insertion and removal after only a week’s worth of experience.

Vision was measured at 20/30- in the right eye and 20/20- in the left eye. Over-refraction in the right eye was -0.50 -1.50 x 100 which improved the vision to 20/25+ and over-refraction in the left eye was +0.50 DS which improved vision to 20/20+. Both lenses exhibited good positioning and minimal movement. Scleral landing in the left eye was acceptable; however, significant compression and blanching were noted nasally and temporally in the right eye. Mild conjunctival prolapse was also noted inferiorly in the right eye. Fluorescein dye was applied over top of the contact lenses and then evaluated. Fluorescein bleeding was seen from the superior aspect of the lens in the right eye. After some perfusion under both lenses, proper limbal clearance and no peripheral corneal touch was confirmed with a wratten filter. Sagittal depth was measured with AS-OCT at 245 µm in the right eye and 262 µm in the left eye. Peripheral clearance was also evaluated with AS-OCT and showed moderate-to-excessive clearance, slightly more in the right eye. Automated keratometry over the right contact lens did not show lens flexure despite the worsened compression, suggesting there may be need for a front toric in the future. The lenses were then removed and no corneal staining, epithelial bogging, or conjunctival limbal adherence was noted. There was clinically significant rebound redness and conjunctival fluorescein pooling in the nasal and temporal quadrants in the right eye.

Based on our clinical experience with the amount of scleral compression in the right eye, we chose a 4 diopter toric haptic flat in the horizontal meridian which provided 120 µm of lens toricity to improve scleral alignment. Many scleral lens companies now provide toric peripheral curve diagnostic lenses to facilitate a more precise initial selection. Over-keratometry suggested that a front surface toric would also be needed; however, we opted to achieve proper scleral apposition before addressing the final power. Achieving proper scleral alignment with a toric haptic first ensured lens flexure was not the cause of the astigmatic over-refraction. Also, establishing the final lens position of the toric haptic is necessary for calculating the final power and location of the front surface toric. Additionally, a slight prescription revision was made for the left lens. The lenses with new parameters were ordered and the patient was scheduled for a follow up visit in one month.

Second Lens Order: Zenlens™ Scleral Lens – Boston XO2™

OD: Oblate Design, BC 9.7, Sag. Depth 4970 µm, Diameter 17.0 mm, Power: +4.75D, Standard Landing Zone, 4 Diopter Toric Haptic

OS: Oblate Design, BC 9.1, Sag. Depth 5100 µm, Diameter 17.0 mm, Power: +4.00D, Standard Landing Zone, Standard Peripheral Curve

This set of lenses was picked up by the patient within a week of ordering. A brief slit lamp examination was performed to confirm improved scleral alignment in the right eye as well as AS-OCT to confirm acceptable central sagittal depth (235 and 255 µm in the right and left respectively). He was instructed to resume full-time wear and follow as planned to evaluate for further revisions.

Visits #4: Follow-Up for Second Lens Order

The patient presented back to our office noting that his right eye felt much better and the redness during and after lens wear had almost completely resolved. He also noted that the vision in the left eye was excellent, however, the right eye was still rather blurry. Vision in the right eye was measured at 20/50- and 20/20+ in the left eye. Physical examination showed a proper fitting back toric lens in the right with good scleral apposition in both eyes. Moderate conjunctival hooding/prolapse was now noted in both eyes, right eye worse than the left (Figures 9 and 10). The sagittal depth was significantly reduced but still acceptable and measured with AS-OCT at 150 µm in the right eye and 145 µm in the left eye. Over-topography did not show lens flexure and over-refraction in the right eye continued to show residual astigmatism (-0.75 -1.25 x 100) which improved best corrected vision to 20/25. Over-refraction in the left eye was plano. With the lenses removed, corneal health was stable and unchanged.

This visit required two additional scleral lens revisions. First, the moderate-to-excessive limbal clearance allowed conjunctival prolapse to worsen in both eyes since the last visit; we decreased limbal clearance to limit the space for prolapse. Secondly, despite proper lens landing and a spherical lens implant in the right eye, the continued presence of the astigmatic over-refraction necessitated a front surface toric. The following lenses were ordered and dispensed and the patient was scheduled for another one month follow-up visit.

Third Lens Order: Zenlens™ Scleral Lens – Boston XO2™

OD: Oblate Design, BC 9.7, Sag. Depth 4970 µm, Diameter 17.0 mm, Power: +4.00D – 1.25 x 100, -100 Limbal Clearance, 4 Diopter Toric Haptic

OS: Oblate Design, BC 9.1, Sag. Depth 5100 µm, Diameter 17.0 mm, Power: +4.00D, -100 Limbal Clearance, Standard Peripheral Curve

Visit #5: Follow-Up for Third Lens Order

The patient returned for a follow-up visit one month later. He noted dramatic improvement in vision and comfort was still excellent. He did note some mild depositing of the lenses, but started using enzymatic cleaner with good results. Vision with his scleral lenses was 20/25 in the right eye and 20/20 in the left eye and over-refraction was approximately plano in both eyes. The fit still looked excellent on both eyes although mild conjunctival prolapse was still present inferiorly in the right eye, but much reduced from the last visit. The sagittal depth was consistent to the last visit with AS-OCT measurements around 140-150 µm in both eyes. No further lens revisions were deemed necessary and he was scheduled for a 6 month follow up.

Visit #6: Emergency Visit

The patient returned to our office a few weeks before his scheduled visit, with a very irritated left eye. He noted it had been that way since he woke up and only felt good when his eye was closed or while he wore his scleral lens. Vision was still acceptable at 20/25 and 20/20 in the right and left eyes respectively. Lens fitting was still appropriate and sagittal depth was stable. Anterior segment evaluation without his lenses showed 1+ conjunctival hyperemia, trace-1 anterior chamber response, and a 1.0 mm epithelial defect without infiltrate involving one of his astigmatic keratotomy scars inferior to the visual axis in the left eye. He was diagnosed with a corneal erosion in the left eye. He was place on a prophylactic antibiotic (Tobramycin ophth. sln) 4 times a day in his left eye. A bandage contact lens (Air Optix^® Night and Day^®) was placed in that eye and we followed up with him at 2 and 7 days out from that initial visit to ensure resolution. As recurrent cornea erosions are a common complication of radial keratotomy, we started him on Muro 128 ophth. ung in the left eye at bedtime to lessen the likelihood of additional erosions. After healing, we allowed him to resume scleral contact lens wear and scheduled him for a follow-up visit in six months.

Visit #7: Six Month Follow-Up

The patient returned for his 6-month follow-up visit, over one year out from starting scleral lens wear and he was still very pleased with the vision and comfort of his lenses. No further corneal erosions where noted. Lens evaluation showed good scleral alignment in both eyes with full limbal clearance and a stable central clearance of around 150 µm in both eyes. There was still mild conjunctival prolapse present inferiorly in his right eye; however, no corresponding corneal neovasculization or conjunctival adhesion was noted and therefore, we did not feel that further lens revision was needed. Vision with his lenses was 20/25- in the right eye and 20/20 in the left eye with negligible over-refraction. Repeated corneal topography confirmed no clear progression of the post-refractive ectasia. AS-OCT serial pachymetry difference mapping of the central cornea showed similar values to the initial evaluation in the left eye and potentially some mild central corneal thickening in the right eye. Given the fairly stable testing and lens appearance, he ordered a backup pair of scleral lenses, and a follow up visit was scheduled for six months to monitor corneal health.

Discussion/Alternative Management Options

History and Common Complications of Radial Keratotomy

Radial Keratotomy (RK) is largely considered to be the grandfather of modern refractive surgery. RK was first developed by a Russian ophthalmologist named Svyatoslav Fyodorov for the treatment of myopia¹. A similar procedure was also developed for astigmatism called astigmatic keratotomy (or AK)². These procedures involved making deep relaxing cuts in the cornea to compensate for refractive error. This procedure was quite popular in the United States during the 1980s into the early 1990s with over one million Americans proceeding with this elective procedure. However, by the mid-1980s the literature began to question the effectiveness of this surgery. Chief among them was the Prospective Evaluation of Radial Keratotomy (PERK) study. This nationwide, prospective, multi-center, 10 year review, sponsored by the Nation Eye Institute was the first well-designed study to monitor the long term complications and refractive endpoints of RK. The one and three year results of the PERK study (1984 and 1987) raised eyebrows with strong evidence of variability in refractive endpoints^3,4. However, the final 10 year review (1995) provided quite damning results for an elective procedure that was thought to produce stable results (highlights below)⁵.

While the PERK study suggested this procedure was fairly safe from an ocular health standpoint⁵, by the final publication of the 10-year study, shockingly 40% of patients were greater than 1.00 diopter from their targeted endpoint and 43% of patients shifted 1.00 diopter or more hyperopic⁵. Results like these, coupled with the United States Food and Drug Administration (FDA) approval of the excimer laser for laser-assisted in situ keratomileusis (LASIK) in 1992, resulted in the demise radial keratotomy. However, many of these early adopters are still suffering the adverse effects of RK decades later. The scars on the cornea cause two main types of complications: mechanical and refractive.

The deep cuts (often to near Bowman’s membrane) coupled with the intraocular pressure pushing outward, allows the cornea to relax to compensate for refractive error. Scar tissue forms at the adjoining stromal interface, and these deep scars are a constant place of weakness. Trauma testing on human globes showed that RK corneas take much less energy to rupture and the literature contains many case examples following trauma^6,7. Closer to the epithelial surface, scar tissue does not form. Instead, epithelium attempts to cover over these open wounds and falls into the opening creating a plug of epithelium at the wound’s surface. This plug of epithelium within the wound is thicker than normal epithelium, approximately 2-4 times as thick^8,9. This increased thickness means newly formed epithelial cells must travel further than normal to reach the epithelial surface. Many of the migrating epithelial cells die before reaching the surface, creating voids and intermittent loss of contiguous corneal epithelium^8,9. This loss of surface integrity increases the risk of recurrent epithelial erosions (as with our patient) and serves as an opportunistic wound site for delayed keratitis. In fact, over half of microbial keratitis events recorded at RK wounds occurred well after the initial healing period¹⁰.

While the mechanical trauma from the keratotomy incisions can have severe complications, the most common adverse outcome of RK is failure to achieve or retain the refractive endpoint. It is clear from the PERK study that many individuals do not retain the vision they enjoyed early after RK due to progressive hyperopia⁵. The persistent hyperopic shift is caused by the in situ interaction of two ocular components: corneal hysteresis and intraocular pressure. Patients with more severe hyperopic changes tended to have lower corneal hysteresis and higher intraocular pressure. The low mechanical strength of the cornea allows the ocular hypertension to act on the cornea instead of on the optic nerve leading to increased peripheral steepening, central flattening, and progressive hyperopia^11,13. Similarly, the normal diurnal ebb and flow of intraocular pressure alone is enough to also cause diurnal fluctuations in refraction for some patients^12,13. Patients who experienced these complications tended to be more hyperopic in the morning with increased ocular pressure and lower in the evening as the pressure decreased. As with our patient, where his refraction was documented to have changed by 1.75 diopters over just a nine-hour period and by 2.50 diopters if you include our in-office testing. Finally, while it may be impossible to measure how much RK alone affected hysteresis, overall, a lower hysteresis is also strongly linked to glaucoma, and therefore, these patients should be monitored closely for optic nerve head changes¹⁴.

Refractive Correction for Post-Radial Keratotomy Corneas

For the majority of patients, RK provided acceptable vision with 70% of patients reporting satisfactory distance vision without glasses or contact lenses at ten years⁵. Even if the refractive endpoint was not achieved or progressive hyperopia necessitates correction, glasses or even traditional contact lenses are often all that is needed. However, visual fluctuations or increased higher-order aberrations from central flattening, ectasia, or irregular astigmatism, can make traditional correction unacceptable for some patients. For these patients, rigid contact lenses are the best way to provide higher quality and more stable vision.

Rigid gas permeable (GP) contact lenses aid patients with post-RK complications as the rigid nature of the contact lens holds its shape and forms a new, smooth, and unchanging refracting surface. Tears fill in the area between the lens and the unstable cornea resulting in decreased higher-order aberrations and a stabilized visual system. The primary difficulty with fitting a corneal GP contact lens on an RK cornea is the highly oblate corneal topography induced by the surgery. The larger and flatter corneal cap created makes it difficult for a lens to properly center on the flattened fitting zone. This leads to several possible complications including increased lens awareness and discomfort, excessive movement, decentering, or even loss of the lens from the eye. This problem can be overcome by using larger lenses with a reverse geometry design that better matches the oblate topography^20,21.

Hybrid lenses are another potential option for post-RK patients, and may have an advantage over small diameter corneal GPs due to the soft lens skirt. The addition of the soft lens skirt improves comfort with less lid-lens edge interaction, but more importantly the skirt allows the lens to center better on the flattened cornea. While GPs and hybrid lenses are useful, newer lens designs and materials make scleral contact lenses an excellent choice to succeed with these often challenging cases^22,23.

Scleral contact lenses work by vaulting completely over the cornea and resting only on the sclera with tears and saline accounting for the space between. This offers several advantages for the post-RK cornea. First, a lens resting on the sclera is more comfortable compared to a lens resting on the cornea, as the sclera is a much less sensitive tissue. Secondly, the irregular topographical flattening and/or keratoectasia does not greatly factor into the fitting process, as the corneal-contact lens interface does not exist. This vastly improves centration by landing on the normal (by contrast) curvature of the sclera. Additionally, corneal touch, discomfort, and mechanical scarring seen with fitting traditional GP lenses on an irregular cornea are not observed as the lens-corneal interface is absent. Scleral contact lenses are not, however, a panacea, and there are some potential pitfalls that are either unique to, or more of a concern with, scleral contact lenses. Three unique complications with scleral lenses are epithelial bogging, mid-day fogging, and conjunctival prolapse²⁴.

Epithelial bogging presents as non-staining but very irregular corneal epithelium. This is thought to occur from constant saturation from the fluid reservoir, similar to “pruned fingers” after swimming. While visually striking, this complication is transient and disappears within 1-2 months after starting routine scleral lens wear^25,26.

Mid-day fogging is a common complication. As there is minimal turnover of the fluid reservoir, mucus, debris, and epithelial cells build up under the lens and, at high concentrations, cause blurring and fogging of vision. This occurs after several hours of wear and requires removal and reinsertion of the lens with fresh solution. The exact etiology of this is not known, and a multi-pronged approach to decrease fogging is best.

1. Ocular Surface Disease: It is imperative to treat any ocular surface disease, especially lid disease like blepharitis, preferably before scleral lenses are prescribed.
2. Scleral Landing: Make sure the landing zone of the lens has good apposition 360 degrees. Sodium fluorescence applied over top of the lens with a wratten filter is useful to isolate any areas of fluorescein bleeding that would suggest a toric haptic is needed for better alignment.
3. Sagittal Depth: If applicable, a lower sagittal depth also decreases the volume of clouded tears and reduces the symptoms.
4. Lens Size: A smaller diameter scleral lens will cause less mechanical stress of the conjunctiva and trap less mucin-secreting goblet cells under the lens.

Even with an optimally fit scleral lens, fogging may still occur but typically improves over time, with most patients noting far less fogging after the first few months of wear. For added protection against fogging, NPATs can be used to completely or partially fill the scleral bowl before insertion. Non-preserved Refresh Optive^® and Systane Ultra^® are successful and Refresh Celluvisc^® could also be used for severe fogging cases.

Conjunctival prolapse or conjunctival hooding occurs when the suction forces of the scleral lens, in conjunction with the pressure of the blink, pull loose conjunctiva up into the bowl of the scleral lens. This usually occurs inferiorly and is secondary to the slight inferior displacement of the scleral lens causing increased limbal clearance. This is largely considered a benign finding unless synechia forms between the cornea and conjunctiva or neovascularization is noted at the site of prolapse. Although it may be benign, as with our patient, it is best practice to lessen or avoid this complication by decreasing the limbal clearance to reduce the space for prolapse to occur.

While there are some unique challenges with scleral contact lenses, one important factor to keep in mind with all lenses, including scleral lenses, is hypoxia. This is doubly true for scleral lenses as oxygen must travel not only through the GP material, but then diffuse through the tear lens to supply oxygen to the cornea. Research has shown that in order for corneal tissue to avoid edema, the minimum Dk/t required for the central cornea is 24²⁷. Higher central sagittal depths are often needed for post-RK corneas to clear the edge of the mid-peripheral steepening leading to higher central vaults over the flat corneal cap. In these cases, it is more appropriate to use a scleral lens with a true oblate design or modify a prolate design by flattening the base curve while steeping the transition zone for more consistent clearance across the cornea.

In practice, severe corneal edema and other sequelae from hypoxia are thankfully uncommon and corneal neovascularization often regresses when scleral lenses are employed. Nonetheless, it is best practice to maximize the corneal oxygen. This is accomplished by fitting the highest Dk materials, with low sagittal depths (200 µm or less), and thinner lens thicknesses if possible, as well as routinely monitoring scleral lens wearers for hypoxia and edema. In our practice, we utilize serial pachymetry mapping of the central 6 mm of the corneal to watch for subclinical hypoxic swelling. While hypoxia unquestionably exists with scleral contact lens wear, the long-term effects of this mild but chronic oxygen deprivation is not known and fitters should be cognizant of potential complications.

Surgical Options on a Post-Radial Keratotomy Cornea

While most patients who underwent RK are correctable with some form of refractive eyewear, there are some surgical options worth discussing that that are either useful to improve/stabilize vision or are complicated by the history of RK.

Early adopters of RK sought to be free of the need for glasses and contact lenses; however, 30% found themselves back in refractive correction after 10 years⁵. Hot on the heels of the retreat of RK was the FDA approval of the excimer laser for LASIK. There exists much controversy regarding performing laser refractive correction (LASIK, PRK) over top of existing RK scars. Many studies say these procedures are safe and effective^32,33,34. However, other studies suggest a higher incidence of complications such as wound dehiscence or gaping, flap separation, and keratoectasia^35,36.

As lower corneal hysteresis is associated with progressive hyperopia and diurnal refractive changes following RK, one newer option to improve corneal stability is corneal cross linking (CXL). This newly FDA approved procedure involves epithelial removal and saturation with Riboflavin (vitamin B2) followed by exposure to a precise wavelength of ultraviolet light (365 nm). This process causes additional bonds to form between the corneal collagen fibers resulting in strengthening and increased hysteresis of the cornea³⁷. Studies show that CXL for RK complications appears to stabilize these corneas with minimal complications; however, longer term studies are needed^38,39.

If the corneal complications are particularly severe, or if the patient is intolerant to medically necessary contact lenses, there are more invasive surgeries. One such option is the purse string suture. This long circular intrastromal suture, when tightened like a purse-string, will plump up and steepen the central cornea to overcome post-operative hyperopia⁴⁰. Finally, if all options have been exhausted, a penetrating keratoplasty can be performed, as a history of RK does not appear to complicate a corneal transplant⁴¹.

Cataract Surgery after RK

Cataract extraction is one of the most commonly performed procedures in the United States with approximately three million Americans receiving this vision restoring surgery every year. Patients that received RK in the 1980s and 1990s have been reaching the point of needing this vital surgery. However, there are substantial challenges that must be overcome to protect corneal health, as well as, obtain a satisfactory refractive endpoint after surgery.

The biggest problem faced by cataract surgeons for RK corneas is calculating the intraocular lens power in the presence of an unstable, overly flattened cornea with higher-order aberrations. Many different calculations and specialized equipment have been purposed as superior for obtaining this necessary value; however, there is discrepancy as to what method or instrument is best^42,43. Therefore, it is important that patients understand that the calculated intraocular lens power is solely an estimate. Even with an uncomplicated surgery there is still high probability of needing glasses and contact lenses for distance vision after the surgery.

In addition to refractive calculations, the radial scars often complicate the surgery itself. Wound dehiscence is well-documented during cataract extraction when utilizing a clear corneal incision, this complication often requires a stitch to close the wound and/or adjacent RK scars. If at all possible, avoiding the RK scars with the stab incision is best. However, with 12-cut or more RK or if the scars extend to the limbus, it may be difficult to find unscarred cornea for the incisions. In this case, it may be most appropriate to tunnel through the scleral adjacent to the limbus or place a prophylactic suture at adjacent RK scar(s), both of which are shown to prevent scar dehiscence^44,45.

Conclusion

Radial keratotomy has afforded many patients freedom from glasses and contact lenses. However, for many early adopters of refractive surgery, this procedure has caused problems, frustration, and unfortunately for many, vision loss. While some of these complications can result in corneal damage such as wound gaping, corneal erosion, keratoectasia, or globe rupture, most long-term complications are refractive in nature.

Decreased corneal hysteresis in conjunction with intraocular pressure can result in excessive central corneal flattening, irregular astigmatism, increased higher-order aberrations, diurnal refractive changes, and progressive hyperopia. Luckily, most of the visual complications are ameliorated with medically necessary contact lenses. Hard contact lenses cover the irregular flattened cornea to better correct for higher order aberrations and high irregular prescriptions. The best options for post-RK correction are larger diameter, reverse geometry corneal RGPs, hybrid lenses, or scleral contact lenses. Scleral lenses offer some unique benefits, but also have some unique challenges. Overall, we decided scleral lenses were the best option for this case.

Our patient was an intriguing case. While he did suffer progressive hyperopia, irregular astigmatism, and even mild keratoectasia, what was especially interesting was the diurnal refractive changes that caused visual fluctuations after cataract surgery. His continued success years after the initial fitting, coupled with a lack of corneal complications from daily wear, shows that scleral lenses are a safe and effective method for overcoming the complications and sequelae of radial keratotomy.

References

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