Optical Media, Properties, and Uses in Eyecare

Flashcards covering definitions, classifications, formulas, and clinical applications of optical media and refracting surfaces in eyecare.

What is an optical medium?

Any space that light can pass through undeviated (such as air or vacuum) or any material which allows light to pass through undeviated or deviated - refractive (such as glass, water, plastic, etc.).

What constitutes an optical system?

A combination of two or more mediums, such as an ophthalmic lens in the air or the eye.

How does a refracting medium affect the vergence of light?

It admits light and bends it as it passes through, thereby altering the vergence of light to a focus (positive focus) or appearing to come from a focus (negative focus).

How is the absolute index of refraction defined according to the text?

It is obtained when the speed of light in a vacuum (where there is no resistance) is compared to that in the air.

When does relative refraction occur?

When the speed of light in air (a rarer medium) is compared to that in another medium (a denser medium).

What is the formula for the surface refractive power of a refracting surface?

$$F = \frac{n-1}{r}$$

What distinguishes a selective transparent medium from a non-selective transparent medium?

A selective transparent medium is opaque to some light while transparent to some form of light, whereas a non-selective transparent medium allows all forms of light to pass through it.

What is an isotropic (isotrophic) medium as defined in the notes?

A medium in which the property is the same in all directions (e.g., glass), unlike a heterotrophic medium where the property is otherwise.

What characterizes a homogenous medium compared to a heterogenous medium?

In a homogenous medium, the property is the same in all directions throughout the mass, whereas in a heterogenous medium it is not.

What are the two routine test applications of ophthalmic prisms?

As a dissociating prism (for temporal disruption of fusion or suppression of the coordination of the two eyes) or as a measuring prism (to determine deviation magnitude in one eye relative to the other or to determine the strength of innervation of an abducting or adducting muscle group - fusional reflex).