A rigid gas-permeable (RGP) contact lens fitted for keratoconus provides better vision than spectacles primarily because:
- A The rigid lens maintains a stable anterior refracting surface by filling the irregular corneal surface with a tear-lens meniscus ✓
- B It increases oxygen supply to the keratoconic cornea
- C It reduces progression of keratoconus by mechanical flattening of the cone
- D It corrects the high myopia but not the irregular astigmatism
Correct answer: A. The rigid lens maintains a stable anterior refracting surface by filling the irregular corneal surface with a tear-lens meniscus
Explanation
In keratoconus, the cornea is irregularly astigmatic; spectacle lenses cannot correct irregular astigmatism. An RGP lens creates an artificial anterior refracting surface by bridging the irregular cone apex with a smooth, spherical/aspheric front surface. The tear-lens (lacrimal lens) filling the space between the back of the RGP and the irregular cornea neutralises the irregular astigmatism. RGPs do not halt progression (CXL does) and do not flatten the cone permanently.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.