
CASE OVERVIEW
A 25-year-old male was referred to the Bochner Eye Institute for keratoconus treatment in 2008. Computerized topography showed inferotemporal steepening in both eyes associated with corneal thinning and posterior elevation. These findings were consistent with bilateral keratoconus. We discussed the risks and benefits of corneal cross-linking combined with topography-guided PRK (TG-PRK). Surgery was performed without difficulty and best-corrected vision improved over 3 to 6 months.

The preoperative topographic image of the right eye is noted above, which showed a maximum steepness of 47.7 diopters and marked irregular astigmatism. Best-corrected spectacle acuity in the right eye was 20/60.

The patient returned for a series of follow-up visits, and was most recently seen 16 years later. The topography image is noted above, which shows a marked decrease in corneal irregularity with an improvement in best-corrected vision with glasses to 20/25.

A computerized topographical difference map is shown above, which highlights how the TG-PRK reduced the corneal irregularity by flattening the inferotemporal cornea by as much as 5.7 diopters and steepening the superior cornea by as much as 3.3 diopters.
KEY POINTS TO UNDERSTAND:
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Primary Goal of CXL: The main purpose of corneal cross-linking (CXL) is to stabilize the cornea and reduce the likelihood of needing a corneal transplant. While most CXL patients are under 35 with progressive disease, it’s important to recognize that older patients may also have active disease.
- Acuity and Keratoconus Diagnosis: Best-corrected spectacle acuity is reduced in keratoconus when topographic changes overly the pupil. The ideal time to diagnose keratoconus is when visual acuity is still 20/20, and topographic changes are outside the pupil. A high degree of suspicion is necessary for early diagnosis.
- Impact of Early Diagnosis and Treatment: The earlier keratoconus is diagnosed and treated with CXL, the better the long-term visual outcomes. Patients as young as 10 years old have been successfully treated with excellent long-term results.
- Corneal Imaging for Diagnosis: Patients experiencing a decrease in best-corrected acuity should undergo corneal imaging to rule out keratoconus, as a slit lamp alone is not adequate for detecting early keratoconus.
- Differential Diagnosis for Irregular Corneas: Not all irregular corneas indicate keratoconus. Other conditions to rule out include dry eye with punctate keratopathy, Salzmann’s nodular degeneration, corneal warpage from hard contact lenses, poor fixation during corneal imaging, Amiodarone keratopathy, and corneal scarring.
- Purpose of TG-PRK: TG-PRK (topography-guided photorefractive keratectomy) is performed to enhance best-corrected acuity, not uncorrected acuity.
- TG-PRK and Corrective Options: Reducing irregular astigmatism with TG-PRK may enable patients to function with glasses and/or soft contact lenses.
- Ideal Candidates for TG-PRK: The best candidates for TG-PRK have clear corneas, a minimum thickness of over 430 microns, and a dioptric difference across the cornea of less than 10 diopters.
- Bilateral CXL Recommendation in Younger Patients: For patients under 25 who present with unilateral keratoconus, it is advisable to recommend CXL in both eyes due to the high likelihood of developing bilateral keratoconus.
- Stable Keratoconus and TG-PRK Candidates: Patients with stable keratoconus who are intolerant to contact lenses or prefer to wear soft lenses or glasses may be candidates for TG-PRK.