What is the next best step for a patient with blurry vision, a K max of 50 diopters (D) and a corneal thickness of 420 micrometers (µm), who is requesting crosslinking?

Management of Keratoconus with Corneal Thickness of 420 μm

The next best step for this 48-year-old male with blurry vision, K max of 50 D, and corneal thickness of 420 μm requesting crosslinking is to recommend alternative treatment options as corneal crosslinking (CXL) is contraindicated due to insufficient corneal thickness.

Contraindication for Standard CXL

• A corneal stromal thickness below 400 μm at the time of UV light exposure is a contraindication for standard CXL due to the risk of endothelial damage 1
• While this patient's corneal thickness is 420 μm, the epithelial removal during standard epi-off CXL would reduce the stromal thickness below the 400 μm safety threshold 1
• Thin corneas are at higher risk for complications including corneal edema from endothelial damage during CXL 1

Alternative Management Options

Modified CXL Approaches

• Hypotonic riboflavin can be used to transiently thicken the cornea to reach the 400 μm threshold in borderline cases 1
• Other methods such as contact lens-assisted CXL or transepithelial CXL could be considered, though these are not FDA-approved in the United States 1
• The sub400 protocol described by Hafezi et al. customizes UV irradiation time based on corneal thickness for patients with stromal thickness between 200-400 μm 1

Contact Lens Management

• Gas-permeable contact lenses can mask corneal irregularities and provide a regular anterior refractive surface, improving vision without surgical intervention 1
• In mild to moderate keratoconus, rigid gas-permeable lenses can provide acceptable vision while avoiding the risks of surgical procedures 1

Intrastromal Corneal Ring Segments (ICRS)

• ICRS can be considered for patients with clear central corneas and corneal thickness of 400 μm or greater to create a more uniform corneal contour 1
• These devices improve uncorrected and corrected visual acuity, reduce high-order corneal aberrations, and facilitate contact lens fitting 1

Assessment Before Treatment Decision

• Complete a thorough corneal tomography evaluation to determine the extent of the disease and establish a baseline to monitor for progression 1
• Assess for the presence of Vogt striae, Fleischer ring, or corneal scarring, which may influence treatment decisions 1
• Evaluate the patient's visual function, including checking visual acuity with multiple Snellen lines to assess the true functional impact 1

Special Considerations

• The patient's age (48 years) is a factor to consider, as CXL complications occur more frequently in patients older than 35 years 1
• The K max of 50 D indicates moderate keratoconus, but is below the 58 D threshold associated with higher CXL failure rates 1
• If progression is documented and CXL is still desired, referral to a specialist with experience in modified CXL protocols for thin corneas would be appropriate 1

Follow-up Plan

• If alternative treatments are chosen, regular monitoring with corneal tomography every 3-6 months is essential to detect any progression 1
• Patient education about avoiding eye rubbing is crucial, as this has been linked to keratoconus progression 1
• If the disease remains stable with conservative management, continue monitoring; if progression occurs, reconsider surgical options with appropriate modifications for thin corneas 1