If an RGP lens is fitted flatter than the cornea, the lacrimal lens power is which sign?

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Prepare for the NBEO Physiological Optics Test with flashcards and multiple choice questions, each offering hints and explanations. Equip yourself for your exam!

Multiple Choice

If an RGP lens is fitted flatter than the cornea, the lacrimal lens power is which sign?

Explanation:
The tear film between the cornea and a rigid lens acts as a tiny lens whose power depends on how the lens curvature compares to the cornea. If the RGP lens sits flatter than the cornea, the tear layer forms a divergent, or minus, lens. That mismatch causes light to spread out more between the surfaces, reducing convergence. So the lacrimal (tear) lens power becomes negative.

The tear film between the cornea and a rigid lens acts as a tiny lens whose power depends on how the lens curvature compares to the cornea. If the RGP lens sits flatter than the cornea, the tear layer forms a divergent, or minus, lens. That mismatch causes light to spread out more between the surfaces, reducing convergence. So the lacrimal (tear) lens power becomes negative.

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