Optics and Refraction — Flashcards

Flashcard 101: The tolerable limit of aniseikonia is _____%?

Answer: 5-8%

Extra: Aniseikonia is a condition where there is a difference in the size or shape of the images seen by the two eyes. • **Tolerable limit:** Generally up to 5% (some sources cite up to 8% as the upper limit for fusion). • **Clinical significance:** Differences >5% usually lead to symptoms like headache, eye strain, and eventual loss of binocular single vision (fusion failure).

Flashcard 102: High myopia is defined as a refractive error of _____ D or more.

Answer: -6

Flashcard 103: The Placido disk test assesses the curvature of the cornea, which is normally not a perfect sphere but is _____

Answer: Aspherical (Prolate)

Extra: Placido's disk (keratoscopy) projects concentric rings onto the anterior surface of the cornea. It is used to evaluate corneal curvature and regularity, helping to detect conditions like keratoconus and astigmatism. A normal cornea is not a perfect sphere but is aspherical (prolate), meaning it is steeper in the center and flattens toward the periphery.

Flashcard 104: Low hypermetropia: error of _____D or less

Answer: + 2

Flashcard 105: Refractive index of the cornea: _____.

Answer: 1.376

Flashcard 106: Myopia must never be _____-corrected with spectacles.

Answer: over (under/over)

Flashcard 107: A total of _____ Purkinje images are formed in normal eyes.

Answer: 4

Flashcard 108: Jack-in the box is seen in the correction of aphakia with _____

Answer: spectacles

Flashcard 109: The refractive index of lens cortex is _____ than lens nucleus

Answer: less

Flashcard 110: In high myopia, it is better to slightly _____-correct for distance

Answer: under (over/under)