Question

9. What statement about the cornea is INCORRECT?

A. It mediates the majority of light refraction

B. It refracts less light than the lens does

C. It can be re-shaped by LASIK

D. It has a refractive power of about 42 diopters

E. It is positioned anterior to the lens

10. When comparing rod photoreceptors to cone photoreceptors, which statement is INCORRECT?

A. Cones are responsible for daylight vision, whereas rods mediate night-time vision

B. Cones are much more sensitive to single photons than rods

C. Cone and rods have uneven distribution across the retina with more rods in the periphery and more cones

in the fovea

D. Cones outnumber rods about 20-fold

E. B and D

11. What would you estimate the membrane voltage of a photoreceptor to be in the dark?

A. -70mV

B. 0mV

C. -40mV

D. +40mV

E. -100mV

12. Imagine you are sitting in a dark room and then someone turns on a lamp near you. What will happen in the photoreceptors in your retina?

A. Light is absorbed by 11-cis retinal in the photoreceptors’ outer segments

B. Cyclic GMP levels rise drastically

C. Sodium influx into outer segments will increase

D. Glutamate release will be reduced

E. A and D

Answer 1

9. B. It refracts less light than the lens does.

Cornea refracts 80% of the light, lens refracts 20% of the light.

10.E. B and D.

Rods are more sensitive than cones and rods outnumber cones by the ration of 20:1.

11. C. -40mV.

12. E. Aand D.