Experience with CXL, Topography-linked PRK, Intacs, & Phakic IOLs
Over the past years 6 years, we have performed over 4,000 CXL procedures and/or CXL combined with a topographically-linked PRK. In addition, in selected keratoconus patients, we have inserted either intracorneal rings or toric phakic IOLs. Here are our top 10 lessons learned in the surgical management of keratoconus.
1. CXL is successful in halting keratoconus progression in 98% of eyes. Success rate is higher for corneas that are clear and are less than 60
2. CXL should be performed on patients as young as possible to halt disease progression and loss of best-corrected spectacle acuity. We have treated patients as young as 10 years of age with corneal stability over a followup period of up to 6 years.
3. Bilateral CXL should be performed in patients under 25 years of age with unilateral disease. Theoretically the “normal” eye can be followed for signs of disease progression, but unfortunately in some cases the disease can progress rapidly with a loss of best-corrected spectacle acuity. Since keratoconus occurs bilaterally in over 90% of patients we feel it is clinically prudent to perform bilateral CXL in younger patients.
4. Specialized Riboflavin solutions can induce corneal swelling by at least 100 microns. Preoperatively this means that a 350 micron cornea prior to epithelial removal can usually be treated by CXL. The only corneas that cannot be swollen to any significant extent are those with corneal scars.
5. The combination of a topographically-linked PRK (TG-PRK) with CXL offers the best chance of improving best-corrected spectacle visual acuity. TG-PRK utilizes preoperative topography maps to guide the excimer laser to flatten steep areas and steepen flat areas. This can result in a decrease in irregular astigmatism and improvement in best-corrected spectacle acuity. Thicker corneas allow for treatment using larger optical zones which have a greater effect. In addition, corneas with less than 10 diopters of difference in the central pupillary area tend to have a greater reduction in irregular astigmatism.
Postop—————————- Preop—————————- Difference Map
In the case above, note the preop inferior to superior difference of around 10 D. This allowed for successful treatment of the irregular astigmatism by flattening the inferior cornea by 4.8 D and steepening the superior cornea by 4.7 D.
6. Diagnosis of keratoconus should be made using elevation topography (eg Pentacam), and a careful slitlamp exam. Elevation topography evaluates both anterior and posterior corneal elevation and produces a pachymetry map. Pseudokeratoconus can occasionally be seen using only computerized topography. It is not uncommon for the following conditions to create a pseuokeratoconus pattern: epithelial basement membrane dystrophy (see images below), superficial punctate keratopathy, amiodarone keratopathy, focal corneal scars, and Salzman’s nodular degeneration.
7. TG-PRK is a more customized approach than intracorneal rings. Usually one or two rings are inserted in the midperiphery. We reserve corneal rings for thin central corneas in which TG-PRK cannot be performed. Rings are typically inserted in advanced cases to allow enhanced contact lens wear.
8. Best-corrected spectacle acuity can take 6 months to be achieved after CXL or CXL with TG-PRK. It takes time for epithelial maturation to occur. The epithelium can undergo hyperplasia and/or hypoplasia to smooth the corneal surface.
9. Patients at any age with stable keratoconus may benefit from CXL and TG-PRK to improve best-corrected spectacle acuity. By reducing irregular astigmatism, patients may achieve satisfactory vision with glasses or soft contact lenses.
10. Stable keratoconus patients with minimal irregular astigmatism, that desire an improvement in uncorrected visual acuity may benefit from a toric implantable contact lens. However, if the refractive error is low then PRK can be performed with limited CXL. This CXL procedure is associated with minimal corneal flattening which results in a more predictable refractive outcome.
I hope you find these clinical observations of interest in the management of keratoconus. If you have any questions or comments please feel free to contact me at info@Bochner.com.
Raymond Stein, MD, FRCSC
Medical Director, Bochner Eye Institute
Associate Professor of Ophthalmology, University of Toronto