On performing refraction using a plane mirror on a patient who has a refractive error of –3 D sphere with –2 D cylinder at 900 from a distance of 1 metre under no cycloplegia, the reflex would be seen to move –
**Question:** On performing refraction using a plane mirror on a patient who has a refractive error of –3 D sphere with –2 D cylinder at 900 from a distance of 1 metre under no cycloplegia, the reflex would be seen to move –
A. vertically
B. horizontally
C. diagonally
D. none of the above
**Correct Answer:** **D. none of the above**
**Core Concept:**
In the process of refraction, the patient is asked to look into a plane mirror placed at a distance of 1 meter from the patient. The patient's eye is tested for both sphere and cylinder power under no cycloplegia conditions. In this case, the patient has a refractive error of -3 D sphere with -2 D cylinder at 90 degrees from the horizontal axis.
**Why the Correct Answer is Right:**
When the patient looks into the mirror, the reflected image of the retina is formed on the mirror's surface. The patient is asked to move the mirror closer or farther away from the eye to find the point where the image becomes sharp (refractive error correction). In this scenario, the patient has both sphere and cylinder errors.
**Why Each Wrong Option is Incorrect:**
A. Vertical movement of the mirror will not affect the image formation on the mirror's surface, as the vertical movement is orthogonal to the plane of the mirror.
B. Horizontal movement of the mirror will also not affect the image formation, as the horizontal movement is also orthogonal to the plane of the mirror.
C. Diagonal movement of the mirror will also not be useful, as it is a compound movement of both horizontal and vertical axis, which is orthogonal to both axes of the mirror.
D. None of the above movements will not help in correcting the refractive errors, as they are all orthogonal to the plane of the mirror.
**Clinical Pearl:**
In refraction, the only axis on which the mirror should be moved is the axis of the cylinder error (the 90-degree angle in this case). By moving the mirror on the axis of the cylinder, the image formation on the mirror's surface can be adjusted to bring the image onto the retina. This is achieved by moving the mirror along the cylinder axis, which will rotate the image and bring it into focus on the retina.