Question

Using Corneal Reflections to Measure the PD without a Pupillometer: The dispenser is positioned at a near working distance. The dispenser holds a pen light directly _____ his or her eye and shines it into the eye of the subject. The subject looks either at the pen light or the dispenser's eye. The reflection of the light on the cornea is used as the reference point instead of the geometrical center of the pupil.

A) Below
B) Above
C) In front of
D) Behind

Answer 1

The dispenser holds a pen light directly in front of his or her eye to measure PD without a pupillometer. This mimics the process of using a keratometer to measure corneal curvature by utilizing the magnification of reflections on the cornea.

Step-by-step explanation:

When using corneal reflections to measure the Pupillary Distance (PD) without a pupillometer, the dispenser holds a pen light directly in front of his or her eye and shines it into the eye of the subject. The cornea of the eye acts like a convex mirror, and the reflected light is used to determine the measurements necessary for fitting eyewear or contact lenses correctly. This method is akin to how an optometrist might use a keratometer to measure the curvature of the cornea for contact lens fitting.

To calculate the magnification in such a scenario, you would use the formula m = -di/do, where m is the magnification, di is the image distance (typically a negative value as it is a virtual image behind the mirror), and do is the object distance. Knowing the magnification, one can then calculate the radius of curvature of the cornea, which is twice the focal length of the corresponding convex mirror.