Ametropia/Ophthalmic Optics Flashcards

A spectacle lens with a base curve of +6.00 D and back surface power of -2.00 D has a front vertex power of approximately:

Answer: +4.00 D

In a thin lens approximation, total power = front surface + back surface = +6.00 + (-2.00) = +4.00 D.

The far point of a 5.00 D myope is located:

Answer: 20 cm in front of the eye

Far point distance = 1/F = 1/5.00 = 0.20 m = 20 cm in front of the eye for a myope.

Chromatic aberration in the eye causes violet light to focus:

Answer: In front of red light

Short wavelength (violet) light is refracted more strongly than long wavelength (red) light, so it focuses anterior to red.

A +3.00 D thin lens in air has a focal length of:

Answer: 33.3 cm

Focal length f = 1/F = 1/3.00 = 0.333 m = 33.3 cm.

Which condition is characterized by a refractive error caused by increased axial length without any change in corneal or lenticular power?

Answer: Axial myopia

Axial myopia results specifically from an elongated globe, placing the retina behind the focal point of the optical system.

When converting a minus cylinder prescription to plus cylinder form, the new axis is:

Answer: Rotated 90 degrees

Transposing a prescription requires rotating the axis by 90 degrees, changing the cylinder sign, and algebraically combining cylinder with sphere.

The index of refraction of CR-39 plastic is approximately:

Answer: 1.50

CR-39 (allyl diglycol carbonate) has an index of refraction of approximately 1.50, making it the standard plastic lens material.