Final answer:
True, the measurement taken by corneal reflex PD Instruments is an objective measure of corneal reflection, not the individual's line of sight. Devices such as keratometers use this principle to measure corneal curvature by analyzing the light reflection, which then helps in determining the cornea's radius of curvature for applications like contact lens fitting.
Step-by-step explanation:
The statement that corneal reflex measurements with PD (Pupillary Distance) Instruments assume correspondence with the subject's line of sight but are actually an objective measurement of the position of the corneal reflection, not the eye's line of sight, is true. This is a key concept in ophthalmology and optometry, particularly when using devices like a keratometer. The keratometer measures the curvature of the cornea by analyzing the reflection of light from its surface, acting like a convex mirror.
When a keratometer is used, it doesn't measure where the person is looking (their line of sight), but rather where the light is reflected on the cornea. For instance, if an object is held 3.00 cm from a person's cornea and the reflected image measures 0.167 cm high, the magnification can be calculated, which can then be used to find other values such as the image distance and the cornea's radius of curvature. The concept of radius of curvature is also connected to the focal length of the convex mirror formed by the cornea, with the relationship that the radius of curvature is twice the focal length.