With the introduction and continually improving options in scleral contact lens technology, optometrists can often successfully manage the visual needs of patients who have moderate to advanced keratoconus (KCN). Additionally, due to corneal collagen crosslinking’s (CXL) ability to slow or even prevent the progression of KCN, ODs are compelled to detect and/or diagnose the condition at its earliest possible stage.1 (See “KCN Classification: An Overview,” below.
So, when should CXL precede contact lens fitting in these patients? The chief considerations are patient age, progression evidence, and visual disability level.
KCN Classification: An Overview
Numerous classification systems for defining the stages of KCN have been developed over the years. The most current ones rely upon indices generated via tomography, which permit detection at the earliest stage. The primary care optometrist without access to tomography should refer out at the earliest suspicion of KCN, based upon reduction of best-corrected visual acuity, accompanied by an increase in astigmatism, particularly when it presents asymmetrically. Moderate-to-advanced KCN is staged by keratometry values, posterior corneal elevation, and corneal scarring, among other findings. The observational CLEK study found: mild (steep keratometry [K] < 45 diopters [D]), moderate (steep K between 45 D and 52 D), or severe (steep K >52 D).3
Patient age
Given that KCN progresses most rapidly in patients younger than age 18, it is wise to refer these patients for immediate evaluation by a corneal specialist.1 CXL is FDA approved for patients as young as 14 years of age.
If the uncorrected visual acuity is acceptable or adequate correction can be achieved with spectacles, these patients should be monitored for refractive and corneal stability through the immediate 3-month postoperative period. If contact lenses are required for optimal vision or desired for cosmetic reasons, contact lens fitting can be initiated at this time.
Additionally, a recently diagnosed individual 18 years or older in whom progression is documented (see below), should also be referred for CXL.
Here, too, contact lens fitting can be initiated after CXL. For current contact lens wearers, a change in prescription or fit can be made pending the procedure, but the patient should be educated regarding the likely temporary nature of the vision change. Further, contact lens wear should be discontinued a day or two prior to the initial CXL consultation, as well as before the procedure itself. This way, corneal topography and thickness will be free from the effects of contact lens wear.
Progression evidence
Any patient in whom there is documented evidence of KCN progression should be counseled on the potential benefits of CXL. The topographical metrics most commonly used to diagnose progression are maximal keratometry, anterior and posterior elevation, and tomographic thickness data.1 (See “KCN Classification: An Overview,” above.)
Visual disability level
As optometrists, our primary focus should always be on maintaining the patients’ best functional vision and helping to ensure their best quality of life. Therefore, contact lens fitting can always be initiated before CXL is considered if the patient isn’t achieving adequate spectacle correction. Furthermore, commonly, only minor fitting changes, if any, will be necessary after the procedure.
Managing expectations
Optometrists must educate patients that CXL is not a “fix” for their vision but, rather, a procedure to help stabilize their eyeglass prescription or contact lens fit. The keratoconus patient is. indeed, a patient for “life” as corneal monitoring and/or contact lens fit are imperative to maintain the best visual outcomes. OM
References
1. Vohra V, Tuteja S, Gurnani B, et al. Collagen Cross Linking for Keratoconus. [Updated 2023 Jun 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK562271/
