Physiological Optics 2 (KMK)

Question 1

Gullstrand’ s Exact Eye model

Answer 1

Cornea (front and back), humor, lens (core and outer layer) = 6 refractive surfaces
AL = 24mm

Question 2

Reduced Eye Model

Answer 2

SSRI n=1.33, AL=22.22mm, total power = 60D

Question 3

Far point

Answer 3

Farthest point of clear vision with no accommodation

Question 4

Near point

Answer 4

Closest point of clear vision with maximum accommodation

Question 5

Where is the far point for an emmetrope?

Answer 5

Optical infinity

Question 6

Where is the far point for an uncorrected myope?

Answer 6

Located between the eye and infinity (somewhere in front of the retina), a real object

Question 7

Night myopia

Answer 7

More myopic under low light levels, increased spherical aberration (large pupils) and light levels too low to fully relax accommodation when viewing distant objects

Question 8

Myopia trends

Answer 8

-prevalence at birth 5-22%
-By age 1, few children are myopic
-age 6, myopia of at least -0.50D is only in 2% of kids
-myopia prevalence increases bw 6yo and 20yo, reaching a prevalence of about 20% at 20yo
-myopia prevalence for 20-40yo is about 30% and then declines slightly, with some chance of myopic shift from cataracts at older ages

Question 9

Where is the far point for an uncorrected hyperope?

Answer 9

Located behind the retina and is considered virtual

Question 10

Latent hyperopia

Answer 10

Young hyperopes will accommodate to neutralize their hyperopia, so shows lower amount in subjective vs objective refraction

Question 11

Manifest hyperopia

Answer 11

The amount present in the subjective refraction

Question 12

Absolute hyperopia

Answer 12

The amount of hyperopia that cannot be neutralized with pt’s accommodation

Question 13

Facultative hyperopia

Answer 13

Amount of hyperopia that can be neutralized by accommodation

Question 14

Hyperopia trends

Answer 14

-Prevalence of hyperopia is about 6% in ages 6-15yo
-hyperopic child at 5yo will likely be hyperopic still at 14yo if >+1.5D, or emmetropic at 14yo if bw +0.50 and 1.25, or myopic at age 14yo if <+0.50D
>45yo shows increase in hyperopia with age (for hyperopes and emmetrope)

Question 15

Resolution acuity

Answer 15

Distinguishing a pattern from a uniforms patch of equal luminance (ex. Teller), typical cutoff 40-t-CPDG for young adult

Question 16

Recognition acuity

Answer 16

Resolving high frequencies and being able to recognize what it is, ex. Snellen

Question 17

Minimum Detectable acuity

Answer 17

Thinnest possible wire that is visible (thin wire against blue sky), lowest thresholds (about 1arcsec)

Question 18

Hyperacuity

Answer 18

Directional relationships, tilt, parallel lines, low thresholds (about 3arcsec), result of higher cortical processing

Question 19

MAR

Answer 19

Minimum angle of resolution, measured in arcmin (1/60 of a degree)

Question 20

Snellen fraction to MAR

Answer 20

1/MAR = 20/x

Basically MAR is inverse of Snellen fraction

Question 21

20/20 into MAR and logMAR

Answer 21

20/20 = 1MAR = 0 logMAR

Question 22

How many arcmin does each letter of the Snellen chart subtend

Answer 22

5 arcmin when viewed at 20ft, each bar subtends 1 arcmin

Question 23

Snellen to cpd

Answer 23

600/Snellen denom = cpd
Or
600/cpd = Snellen denom

Question 24

Dynamic retinoscopy

Answer 24

Accommodation involved, ex. MEM, represents lag of accommodation

Question 25

Nott’s Method

Answer 25

Example of dynamic ret, relies on moving the retinoscopy backwards instead of using lenses. The distance for neutrality can be used to find lag of accommodation (lag is further away ret, lead would be closer)

Question 26

Mohindra ret

Answer 26

“Near retinoscopy” performed in dark, monocular (one eye patched), adjustment factor of 1.25D, not as effective as cyclo ret

Question 27

JND

Answer 27

Approx equal to the denominator of the Snellen fraction divided by 100

Question 28

If acuity is 20/150 what is the JND?

Answer 28

1.50D so make them choose between +0.75 and -0.75 lenses

Question 29

0.50 JCC lens rx

Answer 29

+0.50 -1.00 x180

Question 30

Astigmatic dial

Answer 30

Fog the eye to an acuity of approx 20/50, darkest and sharpest lines, add minus cyl until all equal, add minus sphere until BCVA. Rule of 30 is for the axis (line on clock x30 = axis)

Question 31

Duochrome test / bichrome/red-green test

Answer 31

RAMGAP, red add minus, green add plus
(Green focuses first, and should be balanced in front of retina with red behind retina same amount)
Over minused will see green clearer (add plus)

Question 32

When to use cycloplegic refraction

Answer 32

-child with convergent strab (must determine if accom is contributing)
-child with significant esophoria at near
-young adult complaining of HA with no uncorrected hyperopia (look for latent hyperopia)

Question 33

Ocular accommodative demand

Answer 33

Amount of accommodation needed to see an object clearly

Question 34

Ocular accommodation

Answer 34

Amount of accommodation that the eye actually provides (does not always match the demand)

Question 35

Amplitude of accommodation (AoA)

Answer 35

Maximum amount of accommodation possible for a given eye (independent value, inherent ability)

Question 36

Range of clear vision

Answer 36

Refers to all other points analogous to the near and far points but at varying degrees of accommodation

Question 37

A person uses only about ___% of his/her accommodation ability comfortably.

Answer 37

50%

Question 38

Accommodation and Age

Answer 38

Age 10 : 14.00D
Age 20 : 11.00D
Age 50 : <2.00D

Question 39

Estimate amplitude formula

Answer 39

18.50D - 0.3 of age

Question 40

Minimum amplitude formula

Answer 40

15 - 1/4 (age)