Fitting the Surgically Compromised Cornea
Specialty contact lenses are often the best option for post-corneal surgery patients. Here’s how you can handle these challenging cases.
By Beth Summers, OD, MS, and Maayan E. Keshet, MD
Release Date: November 15, 2018
Expiration Date: November 2, 2021
Goal Statement: Contact lenses are an excellent method of visual rehabilitation for post-cornea surgery patients. Understanding the refractive and lens fit issues these procedures can create is the first step to properly fitting these patients in specialty contact lenses. Clinicians must keep in mind these considerations when fitting patients after incisional and laser refractive surgery, intrastromal corneal ring implantation, and various keratoplasty techniques.
Faculty/Editorial Board: Beth Summers, OD, MS, and Maayan E. Keshet, MD
Credit Statement: This course is COPE approved for 1 hour of continuing education credit. Course ID is 59911-CL. Check with your state licensing board to see if this counts toward your CE requirements for relicensure.
Joint-Sponsorship Statement: This continuing education course is joint-sponsored by the Pennsylvania College of Optometry.
Disclosure Statements:
Authors: Drs. Summers and Keshet have no disclosures.
Editorial staff: Jack Persico, Rebecca Hepp, William Kekevian, Catherine Manthorp and Mark De Leon have no discloses.
Corneal surgery often leaves patients with uncorrected refractive errors, including irregular astigmatism and atypical corneal shapes. For many of these patients, contact lenses are an excellent method of visual rehabilitation. However, each of these patient populations presents unique fitting characteristics that can challenge the fitting process. A firm grasp of the common corneal surgeries and the refractive issues they can create is the first step to properly fitting these patients in contact lenses. Here, we discuss the contact lens fitting considerations clinicians must keep in mind when fitting patients after incisional and laser refractive surgery, intrastromal corneal ring implantation and various keratoplasty techniques.
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| Fig. 1. On topography, this cornea post-RK (16 incisions) shows a wide circumferential band of peripheral corneal steepening and an oblate shape with a flatter center and a steeper periphery. |
Blast From the Past: RK
Although it is no longer used, incisional refractive surgery—especially radial keratotomy (RK)—grew in popularity in the early ’90s. Generally, the procedure created four to eight radial corneal incisions (typically 85% to 90% of the corneal depth) to treat myopia. The incisions flattened the meridian and 90º away, and the closer the incisions came to the optical zone, the greater their effect. In addition, increasing radial incision lengths also resulted in greater flattening.1
RK was performed in myopes based on nomograms that included patient age, radial incision length, incision number and optical zone diameter. Because refractive results were inconsistent, staged adjustments were made empirically based on the initial postoperative refraction. Retreatment for highly myopic patients could result in as many as 32 incisions with exceedingly small clear optical zones.
Unfortunately, the initial flattening effect often progressed even 10 years after the initial procedure, causing an unpredictable and substantial hyperopic shift.2 Keratometry may be as low as 30D in patients with a high number of incisions. Up to 40% of postoperative patients suffer from high hyperopic shifts and progressive hyperopia.3 Many patients experience daily refractive fluctuations of several diopters, with greater hyperopia in the morning and a myopic shift at night. Additionally, low oxygen pressure and high altitude can cause temporary hyperopic shifts.1
Incisions that invade the visual axis, greater number of incisions and hypertrophic incisional scars all contribute to more significant irregular astigmatism and higher-order aberrations (HOAs). According to one study, 3% of patients who underwent RK lost two or more lines of Snellen acuity due to irregular astigmatism.2 In some cases, the destabilized cornea may become ectatic and require either penetrating keratoplasty (PK) or specialty contact lenses.
In the mid ’90s, new data warned against the long-term effects of RK on the cornea, and it was abandoned in favor of laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK).2,3
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| Fig. 2. This topography shows a patient with post-LASIK ectasia who was fit into a scleral lens. |
Fitting considerations. Although surgeons no longer perform RK, patients with a history of RK likely need refractive correction and may benefit from specialty contact lenses. Clinicians should keep in mind that these patients can present with increased steepening in the midperiphery, irregular and possibly elevated scarring, fluctuations in vision (especially with soft lenses) and incisional inclusion cysts that can rupture and increase the risk for infection.4 The steeper midperiphery and flat central cornea have a “reverse geometry” or oblate shape, which can affect the lens fitting process (Figure 1).
Although the method used to create the oblate effect in the contact lenses to match the cornea depends on the design and parameters of the lens, clinicians can generally increase the midperipheral clearance and the sagittal depth of the contact lens while reducing the central clearance, flattening the central base curve or both.
Visual quality tends to be better in gas permeable (GP) materials due to the improved neutralization of HOAs. Lens centration may be difficult to achieve, so large-diameter GPs or scleral lenses are usually preferable. Hybrid lenses may be another option to improve comfort without compromising vision. Because neovascularization of the incisions is a possible complication, clinicians should fit with high or hyper Dk material (>100). Poorly fitting lenses, especially small diameter rigid GPs (RGPs), may wear away at the weakened cornea in the RK incisions and lead to corneal perforation.
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| Fig. 3. This is the topography of a patient with two Intacs segments placed for keratoconus and a PK in his other eye. |
Lasers and Keratectasia
In PRK, an excimer laser ablates the de-epithelialized cornea to treat myopia, low hyperopia and regular astigmatism. Research shows more than one diopter of induced astigmatism after PRK occurs in 2% to 5% of patients within one year after surgery due to either a decentered ablation, central islands or post-refractive surgery ectasia.1
LASIK combines a c-shaped lamellar incision with corneal ablation of the stroma underlying the flap. The thickness and diameter of a LASIK flap depends on the instrument (manual keratome or femtosecond laser) used and affects the biomechanical stability of the cornea. Decentered ablations, flap folds and post-LASIK ectasia can all cause induced astigmatism. Additionally, visually significant macrofolds are possible with flap malpositioning or movement.
Post-LASIK keratectasia is, fortunately, declining: the 2006 rate of 1.8% decreased to only 0.05% by 2014.5,6Other than topographical signs of keratoconus, pellucid degeneration or forme fruste keratoconus, the following factors may help clinicians predict post-ablation ectasia: young patient age, increased flap thickness, residual stromal bed thickness less than 250μm to 300μm, higher myopic ablations, percentage of tissue altered over 40% and thin pachymetry (especially when the thinnest point is decentered).7
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| Fig. 4. This cornea with keratoconus has a single Intacs segment placed inferotemporally, as seen on topography. This patient was fit into scleral lenses. |
Fitting considerations. For patients with under- or over-correction following laser vision correction who are either ineligible for or do not desire an “enhancement,” contact lenses are a good option. During the lens fitting process, clinicians must take several factors into consideration, including dryness, fluctuation in refractive error and possibly decreased corneal sensitivity. These are especially relevant the first six months after the procedure.
Eyes with uncomplicated myopic ablations are usually easy to fit into standard sphere or toric soft contact lenses; however, visual quality is often subpar. GPs tend to yield the best visual results, and research shows an aspheric design is best for reducing HOAs under these circumstances.8 Additionally, for corneas undergoing higher ablations that result in a larger difference between a flat central cornea and a steeper periphery, oblate or reverse-geometry lenses are preferred.9 These lenses, though slightly more difficult to fit, provide a better approximation of the corneal profile in high ablation post-refractive surgery.
Eyes with post-ablation ectasia present more of a fitting challenge. Similar to keratoconus, corneal steepening most often occurs inferiorly and can be corrected with many different types of contact lenses, but complicated corneal shapes are often best neutralized by scleral lenses (Figure 2). One study indicates approximately 80% of patients with this condition can successfully wear specialty contact lenses (including small-diameter RGPs, soft toric contacts and hybrids).10 Current success rates may be even higher given recent improvements in modern contact lenses and the popularization of scleral designs.
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| Fig. 5. This patient’s topography reveals diffuse steepening post-PK for keratoconus. The patient was fit into a scleral lens. |
Corneal Implants
Intacs (Addition Technology) is an intrastromal corneal ring segment (ICRS) designed to flatten the cornea and provide some degree of neutralization of the corneal cone. Although Intacs is indicated in the treatment of mild to moderate myopia (ranging from -0.50D to -5.00D with less than 1D of astigmatism), it is also currently used to treat keratoconus.11 These ring segments are indicated for partial or full visual rehabilitation and are often used to try to avoid a corneal transplant (Figure 3). Currently, Intacs is the only FDA-approved ICRS design.
During Intacs placement, the surgeon inserts one or two plastic half rings into the midperipheral corneal stroma. The tunnel used for placement can be created with a manual device or a femtosecond laser. Made of polymethylmethacrylate and available in a range of thicknesses, the device has a set diameter and width and eyelets at either end to aid in placement.
If two segments are placed, they can be symmetric (for global or central cones) or asymmetric (for asymmetric cones, with the thicker segment placed inferiorly). When analyzing single-segment implants with laser-assisted placement, researchers found uncorrected and best-corrected visual acuity significantly improved one year after implantation.12
One literature review indicates that intracorneal ring segment implantation is both safe and effective in improving the uncorrected and best-corrected vision in the majority of patients.13 However, patients who are progressing at the time of implantation may have less than ideal outcomes, as one review found patients who were progressing at the time of implantation and in whom acuity improved in six months experienced regression to preoperative acuity after five years.14 Additionally, corrected acuities of progressive cases had a statistically significant reduction at five years from implantation.14
Complications from Intacs can include decreasing visual acuity, inflammatory reactions, corneal perforation and segment extrusion related to constant eye rubbing and/or improper segment depth placement.15,16
Although one study reported a fairly high explantation rate (12% were removed within one year), no significant complications resulting from the removal were noted.17 Another study found that decreasing visual acuity was the primary reason for explantation, not issues related to implantation or positioning. However, the researchers also found that best-corrected vision and keratometry readings returned to pre-Intacs implantation measurements.15
Combo Procedures for KeratoconusNewer keratoconus treatment methods combine Intacs placement with corneal collagen crosslinking (CXL) to help prevent progression. A recently published study examined a new technique called simultaneous intratunnel crosslinking and intrastromal corneal ring segment implantation.1,2The method involves injecting riboflavin into the corneal channel before segment implantation to increase penetration into the cornea without having to remove the epithelium.1Following segment placement, eyes are exposed to UVA radiation, leading to statistically significant outcome measures (improvement in uncorrected and corrected distance visual acuity, keratometry values and refractive error) similar to epi-off crosslinking after Intacs placement.2
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Fitting considerations. Many studies have emphasized the benefit of Intacs in improving contact lens tolerance. A follow-up study from the original Intacs study found 80% of patients who were previously contact lens intolerant were able to tolerate contact lenses two years after Intacs implantation.18 Another study showed that more than 60% of patients with advanced keratoconus tolerated contacts after Intacs implantation.17 However, these studies did not specify which contact lens designs were attempted before patients with keratoconus were deemed intolerant.
With the increased popularity of lenses other than smaller RGP lenses, especially scleral contact lenses, even patients with high degrees of corneal ectasia tend to be able to adapt to contact lens wear with exceptional comfort and visual acuity.
The popularity of Intacs has been declining in recent years, yet many patients still have the implants and need visual rehabilitation with specialty contact lenses. Successful contact lens fits after Intacs implantation can been accomplished with specialty soft, RGP, piggyback, hybrid and scleral contact lenses.19-22 However, fitting a specialty contact lens over a cornea with Intacs can be more complicated than it is for a patient with keratoconus without Intacs. Most issues are related to difficulty with centration, irregular shape (oblate) caused by the inserts and even erosions in the Intacs area.23 GP lenses are preferably designed in a large diameter due to the physical obstruction to centration caused by the segment(s). Alternatively, hybrids and smaller-diameter GPs with piggyback soft lenses can be beneficial.
When fitting a scleral contact lens, for example, the relative elevation created by the device in the midperiphery must be taken into account (Figure 4). Additionally, the cornea may have a relatively oblate corneal profile due to the flattening effect of the segments. This is generally mild but often warrants an increased midperipheral clearance in scleral lenses.
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| Fig. 6. Topography shows relative central flat and steep periphery (reverse geometry) in a post-PK cornea. This patient was fit into an oblate-shaped (steep skirt) hybrid lens. |
Keratoplasty Cases
Many keratoplasty procedures now exist, including PK, deep anterior lamellar keratoplasty (DALK), Descemet’s stripping automated endothelial keratoplasty (DSAEK) and Descemet’s membrane endothelial keratoplasty (DMEK).
In PK and DALK, a circular incision of the host cornea is created either with mechanical or, occasionally, laser trephination. A circular button of host cornea is excised in its entirety during PK, and all but the host endothelium is removed in DALK. Both surgeries involve the suturing of a donor button in a similar fashion. A 2015 meta-analysis found the rate of graft rejection is lower for DALK, though failure rates are similar.24 The final astigmatism of PK and DALK were not found to be statistically significantly different.24 Postoperative astigmatism is a result of a combination of individual healing responses, suturing technique, graft diameter, centration and progression of ectasia, if present.
Sutures steepen the central cornea along their axis. There is a local flattening immediately around the suture and a compensatory steepening centrally in the graft. Interrupted sutures create the most astigmatism, followed by a single running suture, with the least astigmatism created by a double running suture.25However, selective suture removal in grafts with interrupted sutures affords the greatest control over astigmatism.
Following suture removal, astigmatism decreases or remains the same in 79% of patients who underwent excimer laser keratoplasty, while it increases in 80% of patients who underwent conventional motor trephination.26
For treatment of the corneal endothelium, DSAEK or DMEK are preferred. The procedures selectively remove the patient’s Descemet membrane and endothelium, followed by transplantation of donor corneal endothelium (with some posterior stroma in DSAEK and without stroma in DMEK). Indications include Fuchs’ endothelial dystrophy, pseudophakic bullous keratopathy/edema, failed corneal graft and iridocorneal endothelial syndrome.
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| Fig. 7. This topography reading reveals mild irregular astigmatism following DSAEK for Fuchs’. The patient’s uncorrected visual acuity in this eye was approximately 20/30 and no further correction was desired. |
Fitting considerations. General considerations for fitting contacts for a cornea that has undergone keratoplasty involve patient vision and comfort, as well as graft health and integrity. Luckily, the fitting process is similar for post-PK and post-DALK eyes.
Visual rehabilitation following a PK is almost always afforded by a specialty contact lens fitting. Many post-PK patients experience dryness, and one study found approximately a third of eyes required dry eye management with topical lubrication and punctal occlusion.27 To increase comfort and lens tolerance, clinicians can consider adding Hydra-PEG (Tangible Science) coating to eligible GP lenses.
Maintaining graft health is a top priority for contact lens fitters. Generally, fitting a minimum of six months postoperatively allows for some stabilization in astigmatism and decreased frequency of steroid drops. Additionally, fitting should only be initiated once the eye is stable, no active inflammation or infection is present and sutures are epithelialized. One study found PK sutures are present in 40% of eyes at the initiation of a contact lens fitting.27 High or hyper Dk lens materials are critical to prevent hypoxia, infections and possible graft rejection or failure.
Graft shape will be a significant determining factor as to what lens will work best.
Proper RGP lens fitting should demonstrate no significant bearing on the graft or sutures/junctions. Often, larger-diameter GPs are needed to achieve proper centration. Oblate GP designs may provide better approximation to corneal shape.
Fitting a scleral contact lens over a PK graft can be challenging, depending on the shape and orientation of the graft (Figure 5). Arguably the most important issue is the host/graft junction. Because scleral lenses tend to decenter inferotemporally most often, clinicians should pay particular attention to the superonasal graft junction when monitoring contact lens wear in these patients.
Decentered grafts also can be a challenge to fit, and it is important to evaluate the most elevated point. Highly elevated grafts with relatively flat central curvature are best fit with oblate scleral lenses and increased midperipheral clearance. Scleral contact lenses may be fit over PK grafts with well-epithelialized sutures, but clinicians should take irregular astigmatism caused by sutures into account.
Suture removal may change the ametropia (especially astigmatism) of the eye. Often, elective suture removal for interrupted sutures is performed in the steep meridian in an effort to decrease corneal astigmatism. Contact lens fitters should carefully consider whether an anterior toric prescription (for remaining astigmatism correction) should be incorporated into the lens design when interrupted sutures are still present and astigmatism may possibly change at a later time with suture removal.
Additionally, lens thickness reduction may help to increase oxygen permeability across the lens. However, both reduced center thickness and the higher Dk materials preferred for PK fits may result in lens flexure. To check for this complication, clinicians should perform topography over the lens. Astigmatism on the topography of a lens indicates flexure.
Hybrids may also be beneficial for PK fits, especially considering the availability of newer hybrid lenses with oblate designs. Additionally, steep skirts are a valuable tool to stabilize the lens on an eye with a steep periphery, as they decrease bubble formation in the skirt portion of the lens (Figure 6).
Silicone hydrogel specialty lenses that provide adequate Dk are a possibility, but may not provide a proper fit or vision for complex corneal shapes. Clinicians often achieve greatest success in soft lenses with aberration control and customizable base curves and periphery.
Corneas that have undergone DSAEK or DMEK do not generally require specialty contact lenses, but refractive changes may occur. A study found that anterior corneal shape typically does not change much following a DSAEK; however, patients often demonstrate a hyperopic shift from posterior curvature changes.28 The average hyperopic shift on manifest refraction was +0.670 ±0.158D following a DSAEK.28
Advanced endothelial disease causing anterior corneal changes or stromal scarring may play a role in determining the patient’s final vision in spectacles and need for specialty contact lenses (Figure 7). This effect, however, is often mild.
Fitting patients with contact lenses after corneal surgery can challenge even the most seasoned contact lens fitter. Each case presents a slightly different cornea with its own unique considerations. But the promise of better visual outcomes for these patients is well-worth the hard work in restoring vision for this population.
Dr. Summers is an adjunct assistant clinical professor at SUNY College of Optometry and an optometrist practicing in NYC. She fits specialty contact lenses in an OD/MD setting.
Dr. Keshet is a cornea specialist in private practice in NYC. She is an adjunct assistant clinical professor at SUNY College of Optometry and an educational lecturer.
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