Rigid gas-permeable (RGP) contact lenses are superior to soft contact lenses for correcting irregular astigmatism in keratoconus because:
- A They create a tear lens between the flat back surface of the lens and the irregular cornea, neutralizing irregular astigmatism with a smooth optical front surface ✓
- B They reduce corneal oxygen consumption more effectively
- C They slow the progression of keratoconus by applying mechanical pressure on the cone
- D They correct myopia more accurately than spectacles
Correct answer: A. They create a tear lens between the flat back surface of the lens and the irregular cornea, neutralizing irregular astigmatism with a smooth optical front surface
Explanation
RGP lenses correct irregular astigmatism (as in keratoconus) through the tear lens effect: the rigid lens vaults the irregular cone, and the space between the lens back surface and corneal anterior surface fills with tears. This tear film creates a smooth optical interface that neutralizes corneal surface irregularities. The front surface of the RGP provides the refractive correction. Soft contact lenses conform to the corneal surface and cannot create an effective tear lens, thus failing to correct irregular astigmatism. RGP lenses do NOT halt progression.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.