Corneal asphericity and visual function after radial keratotomy

Area of Science:

• Ophthalmology
• Corneal Surgery
• Refractive Error Correction

Background:

• Radial keratotomy (RK) is a refractive surgical procedure to correct myopia.
• Corneal asphericity, a measure of corneal shape deviation from a perfect sphere, influences visual quality.
• Understanding the relationship between RK parameters and postoperative corneal shape is crucial for visual outcomes.

Purpose of the Study:

• To investigate the correlation between radial keratotomy clear zone size and postoperative corneal asphericity.
• To determine the association between postoperative corneal asphericity and uncorrected visual acuity (UCVA) after RK.
• To explore the potential mechanism by which corneal asphericity affects visual performance in RK patients.

Main Methods:

• Corneal asphericity was measured in 81 eyes before and after RK using keratoscope rings.
• Asphericity was calculated between specific keratoscope rings (2 and 9) corresponding to corneal diameters of 2.3 mm and 7.6 mm.
• Statistical analyses, including correlation and Mann-Whitney U tests, were employed to assess relationships between surgical parameters, asphericity, and UCVA.

Main Results:

• A significant correlation was found between smaller RK clear zones and greater negative postoperative asphericity (R = 0.74, p < 0.0001).
• Eyes with smaller clear zones (< 4.0 mm) exhibited high mean negative asphericity (-6.44).
• Within the smaller clear zone group, higher levels of negative asphericity were associated with better UCVA (Mann-Whitney U test, p < 0.0001).

Conclusions:

• Smaller clear zones in RK surgery lead to increased negative corneal asphericity.
• Increased negative asphericity may beneficially increase the depth of field.
• This effect could explain why some RK patients with residual refractive error achieve better-than-expected UCVA.