The Optometrist’s New Role in Keratoconus Management

Availability of CXL changes the paradigm for care of US patients with keratoconus or corneal ectasia.

By John D. Gelles, OD

Corneal collagen crosslinking (CXL), which has been widely used outside the United States for the treatment of keratoconus and corneal ectasia, received US FDA approval last April. With this approval, the KXL UV-illumination system and the Photrexa and Photrexa Viscous riboflavin solutions (Avedro) became commercially available in this country.

In CXL, an ultraviolet light source is used to irradiate the cornea after it has been soaked in a photoenhancing riboflavin solution. The resulting photochemical reaction increases the number of molecular bonds, or crosslinks, in the corneal stroma, resulting in a stiffened and biomechanically strengthened cornea. The goal of this treatment is to halt or diminish the progressive thinning and steepening of the cornea that occurs in keratoconus and in patients with corneal ectasia after refractive surgery. Keratoconus affects approximately one in every 2,000 Americans and is the leading indication for penetrating keratoplasty (PK) worldwide.1,2

Figure 1. Comparison of penetrating keratoplasty rates during 3-year periods before and shortly after the introduction of CXL in the Netherlands.4

In the multicenter US clinical trial carried out in part at our institution, CXL with the Avedro system was shown to decrease progression of keratoconus and corneal ectasia.3 Practitioners in the United States now have an effective intervention to offer patients with progressive keratoconus or ectasia. In the Netherlands, the introduction of CXL resulted in a dramatic reduction in PK procedures (Figure 1).4 There is also evidence that patients experience reduced anxiety and subjectively better vision- and health-related quality of life after CXL.5,6

For optometrists, the incorporation of CXL into practice presents both challenges and opportunities. On one hand, CXL is an ideal opportunity for collaborative care with ophthalmologists. Optometrists can increase the frequency of monitoring exams for keratoconic and post-LASIK patients, and they can provide and be reimbursed for ongoing medical care. Additionally, optometrists will be able to successfully keep more keratoconic patients wearing contact lenses, and those lenses will be easier to fit and maintain once progression has been stopped and advanced disease has been avoided.

CHANGING PARADIGM

The challenge is that significant changes must be made in how optometrists manage patients with keratoconus. In the old paradigm, a patient might not be diagnosed with keratoconus until there was a combination of subjective and objective findings, such as visual complaints, refraction without a consistent endpoint, large changes in refractive values, reduced best corrected visual acuity, abnormal retinoscopy reflex, irregular mires on keratometry, and overt slit lamp signs (eg, striae, pronounced thinning, scarring, or Fleischer ring), indicating advanced disease. Follow-up included annual examinations to monitor the patient’s condition, while ensuring that he or she achieved adequate vision with contact lenses and comfort without complication. Patients were typically not referred to an ophthalmologist specializing in corneal disease until they were deemed contact lens intolerant, had developed vision-impairing corneal scarring, or had progressed to such an advanced stage that PK was necessary.

With CXL, all of that changes. The earlier the patient is screened, diagnosed, and treated, the sooner one can arrest disease progression and stabilize the cornea using CXL, effectively preventing advanced disease. In recognition of this change, all of optometry and ophthalmology must now incorporate instrumentation capable of effectively screening and monitoring keratoconus. This is especially important for those working with pediatric patients, as the typical presentation of keratoconus is during adolescence.

Early diagnosis of keratoconus involves finding correlations among many corneal metrics, analogous to the correlation of metrics in diagnosing glaucoma. In keratoconus and ectatic disease, these metrics include corneal topography, corneal pachymetry, corneal epithelial thickness, posterior corneal topography, wavefront analysis, and corneal biomechanics. By and large, advanced diagnostic testing for keratoconus has not been widely incorporated into optometric practice.

In the past, even if optometrists could diagnose keratoconus at its earliest stages, they had no treatment options. However, with the advent of CXL as an effective treatment for decreasing the progression of keratoconus, it is important for all optometrists to have the equipment to diagnose and monitor the disease at its earliest stages. Thus, it is recommended that optometrists acquire, at minimum, a Placido disk–based topographer or, better yet, a corneal tomography-based topographer. This will allow proper screening for keratoconus. Optometric practices may want to invest in additional technologies to diagnose and monitor keratoconus and ectasia patients; cost estimates and equipment recommendations are listed in the table.

For a relatively low financial investment that can be recouped in billing for medical eye care, these instruments, which can also be used for contact lens fitting, permit evaluation of changes in several important metrics. To use such technology effectively, it is also important for optometrists to have the proper training in its interpretation. Some tips for interpretation are indicated in Figures 2 and 3.

Figure 2. Comparison of topography and Placido ring mires. The metrics for diagnosis of keratoconus are K > 47.00 D, inferior-superior difference >1.40 D, 6 mm optical zone axis skew > 20° irregular astigmatism.10 From left to right: image sets of mires with corresponding axial maps underneath. Far left image is a normal cornea with symmetric rings. Center left is an eye with keratoconus; note the irregular and asymmetric mires. Note that, in the center right image, the axial map could be mistaken for keratoconus, but on viewing the Placido ring image, it is clear the irregularity is tear film–based, whereas the far right image is true keratoconus with tear-film disruption.

Patients with keratoconus who are younger than 40-years-old and, thus, in the typical progressive lifecycle of the disease, should be scheduled for more frequent exams than in the past. Every 3 to 6 months is appropriate because keratoconus can rapidly progress in a short period of time at this age.

Patients with extremely advanced disease may not be good candidates for CXL, as the photochemical reaction that occurs may damage the endothelium in very thin corneas. A corneal consult is still worthwhile, however, because the hypotonic dextran-free riboflavin solution (Photrexa) can be applied to swell or thicken the cornea enough to achieve the 400-µm thickness needed for safe CXL in some cases.7

MANAGING THE CXL PATIENT

In the US clinical trials that led to FDA approval of the Avedro system, the corneal epithelium was removed (9.0-mm defect) before CXL was performed. Therefore, the protocol in the labeling is an epithelium-off procedure. Afterward, a bandage contact lens is placed and patients are given topical medications, typically four times daily for the first week, similar to post-PRK care. At day 5, the epithelial defect is typically healed and the bandage contact lens is removed. The antibiotic and non-steroidal anti-inflammatory drugs are discontinued, and the steroid is usually continued for another 1 to 3 weeks.

Figure 3. Case study. This patient was lost to follow-up for 1 year. The progression in this untreated eye can be seen by evaluating the mapping and noting the increases in severity that are present in all metrics. The initial map is on the left side, and a map from 1 year later is on the right side. Note the correlation of location of all metrics in keratoconus, including corneal thickness, front and back surface corneal elevation, and anterior corneal contour. The difference map on the bottom (from left to right, follow up – initial = difference) shows only the axial data, but the progression is clear to see. This tomography-based system can allow for earlier detection of keratoconus than a Placido ring–based system as it measures multiple key corneal metrics. Problems common to all topography systems include false irregularities caused by the tear film, mistaking severity of disease due to color scaling, and decentration of image capture.

Although there is some variation, the cornea specialist will typically see patients for the 1-day and 1-week visits and then, once the epithelium is healed, send them back to the optometrist for the remainder of follow-up care.

At 1 month after CXL, visual acuity and keratometric values (Kmax) are a little worse, and it is normal to see light haze.8 This is not the same type of haze seen after PRK; it is transient and seems to have little effect on visual acuity. After 1 month, there is progressive flattening of the Kmax; in the clinical trials for the Avedro system the flattening was an average of 1.7 D.3 Uncorrected and best corrected visual acuity typically improve by about 1 line, and progression stops.3

Somewhat counterintuitively, the cornea may seem to be getting thinner; the collagen bonds tighten and the pachymetry measurements decrease; however, after about 3 months, this stabilizes along with the Kmax and visual acuity. By 1 year after CXL, pachymetry returns to baseline.9

Endothelial cell counts should also be checked during follow-up, as rapid changes in this metric may indicate damage to the endothelium.

Contact lenses may be fit once the epithelial integrity is restored after CXL, typically by 1 month. At that point, vaulted designs that do not rest on the corneal surface may aid in avoiding disruption of epithelial healing. It is important to make patients aware that vision may change slightly during the first few months after the procedure, and their contact lens parameters may have to be updated.

CONCLUSION

In its current iteration, CXL is not a corneal reshaping procedure. Rather, CXL is essentially a “locking-in” of the cornea so that the ectatic condition does not progress further. For fitting purposes, one can expect that the cornea may get flatter with time but likely not clinically significantly flatter; therefore, follow-up during this time is essential.

The benefits are clear: for the patient, there is an improved visual prognosis and less chance of requiring a corneal transplant; for the clinician, it will be easier to care for and provide vision correction for that patient over time. This is why early intervention is essential before there is significant further thinning and distortion.

Now that a CXL treatment is approved to slow progression, it is incumbent upon practitioners to carefully monitor and follow corneal ectatic conditions so that prompt referrals can be made for this essential procedure.

1. National Eye Institute. Facts About The Cornea and Corneal Disease. May 2016. http://www.nei.nih.gov/health/cornealdisease/#12. Accessed January 5, 2017.

2. Eye Bank Association of America. 2014 Eye Banking Statistical Report. http://restoresight.org/wp-content/uploads/2015/03/2014_Statistical_Report-FINAL.pdf. Accessed January 5, 2017.

3. Hersh PS, Greenstein SA, Fry KL. Corneal collagen crosslinking for keratoconus and corneal ectasia: One-year results. J Cataract Refract Surg. 2011;37(1):149-160.

4. Godefrooij DA, Gans R, Imhof SM, Wisse RP. Nationwide reduction in the number of corneal transplantations for keratoconus following the implementation of cross-linking. Acta Ophthalmol. 2016;94(7):675-678.

5. Cingu AK, Bez Y, Cinar Y, et al. Impact of collagen cross-linking on psychological distress and vision and health-related quality of life in patients with keratoconus. Eye Contact Lens. 2015;41(6):349-353.

6. Brooks NO, Greenstein S, Fry K, Hersh PS. Patient subjective visual function after corneal collagen crosslinking for keratoconus and corneal ectasia. J Cataract Refract Surg. 2012;38(4):615-619.

7. Rosenblat E, Hersh PS. Intraoperative corneal thickness change and clinical outcomes after corneal collagen crosslinking: standard crosslinking versus hypotonic riboflavin. J Cataract Refract Surg. 2016;42(4):596-605.

8. Greenstein SA, Fry KL, Bhatt J, Hersh PS. Natural history of corneal haze after collagen crosslinking for keratoconus and corneal ectasia: Scheimpflug and biomicroscopic analysis. J Cataract Refract Surg. 2010;36(12):2105-2114.

9. Greenstein SA, Shah VP, Fry KL, Hersh PS. Corneal thickness changes after corneal collagen crosslinking for keratoconus and corneal ectasia: one-year results. J Cataract Refract Surg. 2011;37(4):691-700.

10. Rabinowitz YS. Keratoconus. Surv Ophthalmol 1998; 42: 297-319.

John D. Gelles, OD, FIAO, FCLSA
• director, specialty contact lens division, Cornea and Laser Eye Institute-Hersh Vision Group and the CLEI Center for Keratoconus, Teaneck, N.J.
• financial interest: none acknowledged
jgelles@vision-institute.com