In retinoscopy with plane mirror at 1 meter distance, if retinal glow moves in opposite direction of the mirror, the person has myopia of
Correct Answer: >1D
Description: Ans. c (> 1 D) (Ref. Khurana Ophthalmology 2nd/pg. 67; Parsons' Diseases of the Eye 20lh/pg. 63).Under the actual conditions of retinosopy at 1 m distance with a plane mirror, when the mirror is titled towards the right side, the immediate source of light moves to the left, and1. in the hypermetropic eye, the circle of light on the fundus moves to the right and the shadow seen in the pupil moves to the right in the same direction as the mirror;2. in the myopic eye (above-1 D) the circle of light on the fundus moves to the right, and the luminous reflex of the fundus seen in the patients's pupil and the shadow seen in the pupil moves against this to the left; in the opposite direction to the mirror'3. in the myopic eye of-l D there is no shadow and the pupil is uniformly illuminated;4. in emmetropic and myopic of less than -1 D there is a very faint shadow moving to the rightMYOPIA (SHORTSIGHTEDNESS)# A discrepancy between the refractive power and axial length of the eye such that parallel incident light rays converge at a focal point anterior to the retina# Whereas parallel incident light rays converge at a focal point on the retina in emmetropic eyes, they converge at a focal point anterior to the retina in myopic eyes. This means that no sharply defined images appear on the retina when the patient gazes into the distance.# The myopic eye can only produce sharply defined images of close objects from which the light rays diverge until they enter the eye.# The far point moves closer; in myopia of -1 diopter it lies at a distance of 1 m.# In myopia, the far point (distance from the eye = A) can be calculated using the formula: A (m) = 1/D, where D is myopia in diopters.# Possible causes include an excessively long globe with normal refractive power (axial myopia) and, less frequently, excessive refractive power in a normal-length globe (refractive myopia).# A difference in globe length of 1 mm with respect to a normal eye corresponds to a difference of about 3 diopters in refractive power.
Category:
Ophthalmology
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