Optics of the Eye

Question 1

Myosis

Answer 1

constriction of pupil

Question 2

Mydriasis

Answer 2

pupillary dilation

Question 3

Emmetropia

Answer 3

normal vision, such that an image from a distant object is on focus on the retina without ciliary m contratction

Question 4

Myopia

Answer 4

nearsightedness such that the image of a distant object is anterior to retina without ciliary m contraction

due to an eyeball that is too long

requires concave (diverging) lens

Question 5

Hyperopia

Answer 5

farsightedness

eyeball that is too short

image of distant object without ciliary muscle constriction is focused posterior to retina, but with muscle can focus on distant objects

can’t focus on near objects, they’re closer than near point

requires convex lens

Question 6

Astigmatism

Answer 6

unspheical curvature of eye, requires cylindrical lens

Question 7

List two mechanisms that determine how much light is refracted (bent) at the air
cornea interface.

Answer 7

the refractive index of the media light was traveling in and the incident angle upon cornea

Question 8

Describe what happens to axial light from infinity when it passes through a:

a. converging lens;
b. diverging lens;
c. cylindrical lens.

Answer 8

converging brings them together, diverging apart, and cylindrical has two different focal lenghts for two orthogonal planes of light

Question 9

Describe the changes in the lens and ciliary muscle during accommodation.

Answer 9

ciliary muscle contraction brings the zonular fibers closer to the lens, releiving tension on it and moving it anteriorly to increase its curvature up to a lens power of 34 diopters

Question 10

List three changes that occur during the accommodation-convergence (near)
reflex.

Answer 10

change in lens shape

miosis (pupillary constriction) to narrow the aperture

bilateral eye convergence

Question 11

Explain how myosis can increase visual acuity

Answer 11

myosis makes the near point of vision practically zero so that without corrective lens someone can focus on an object right in front of the eye

Question 12

presbyopia

Answer 12

this is the declining accomodating ability of the eye

Question 13

Explain for emmetropia, myopia, hyperopia, presbyopia, and astigmatism:

a. Optical defect (if any)
b. Image position of an object at infinity (without/without accommodation)
c. Amount of accommodation required to accurately focus an object located at infinity
d. State of ciliary muscle contraction for objects at infinity and at the near point
e. Optical power of the lens for an object at infinity
f. Near point compared to normal
g. Far point compared to normal
h. Type of lens used for correction

Answer 13

emmetropia: normal
myopia: nearsightedness, image anterior to retina, can’t compensate by accomodation of lens, ciliary m relaxed, high optical power, near point and far point are both nearer, needs converging lens
hyperopia: farsightedness, image posterior to retina, lens accomodates to correct, near and far point are farther, converging lens, less optical power of eye

presbyopia has normal far point and farther near point, requires reading glasses or trifocals

astigmatism requires cylindrical lens

Question 14

what’s the total refractive power of the typical human eyeball?

Answer 14

+59 diopters (remember positive is converging or canvex)

cornea is about 39 diopters, lens is 20