Optics and Refraction — Flashcards

Flashcard 131: In a Placido disk test, **elliptical rings** are characteristic of which condition?

Answer: Corneal astigmatism

Extra: The Placido disk (keratoscope) consists of concentric black and white rings: - **Normal cornea:** Regular concentric circles. - **Corneal astigmatism:** Elliptical/oval rings (the long axis of the ellipse corresponds to the flatter meridian). - **Keratoconus/Irregular cornea:** Distorted or irregular rings.

Flashcard 132: Interpretation of retinoscopy done at 1 m is as follows:No movement of red reflex - Myopia of _____With the movement - Emmetropia, hypermetropia, myopia of _____Against the movement - Myopia of _____

Answer: 1D; less than 1D; more than 1D