The Aging Visual System

There are normal age-related changes in the eye and visual system

Decreased pupil size (miosis) – decreases illuminance but increases depth of focus & decreases aberrations

•Yellowing of the crystalline lens – reduces short wavelength transmission; threshold for blue increases)

•Presbyopia – defocus for near objects

•Gradual decrease in photoreceptor density and other neurons

•Possible decrease in neurotransmitter release

These can affect visual thresholds

Like the rest of our bodies, our eyes and vision can change with age

In addition, ocular pathology is more frequent in the elderly.

•Cataract

•Age-related macular degeneration

•Glaucoma

•Diabetic retinopathy

Need to distinguish pathological changes from normal aging

In addition, elderly patients tend to adopt a more conservative response criterion.

Want to be sure they see something before responding.

This acts to raise threshold (decrease sensitivity)

Get all of these changes some of the time (e.g. in some people)

& none of these changes some of the time

(but don’t get all of the changes all of the time!)

People age at different rates.

Some never develop ocular pathology

The result is greater variability in the range of normal values. This makes it harder to detect pathology at early stages.

What are some normal age-related changes?

Decrease in the rate of dark adaptation

Increase in absolute threshold

Time (min)

0 10 20 30 40

Log Threshold Luminance (lamberts)

2

3

4

5

6

7

8

16-19 20-29 30-39 40-49 50-59 60-69

70-79

80-89

Possible reasons:

Higher threshold: Smaller pupil diameter, less effective light absorption is like wearing a neutral density filter

Slowed rate of dark adaptation: slower regeneration of photopigment

Resolution acuity (MAR) (best corrected) becomes worse

(acuity is worse)

Age (yrs)

40 50 60 70 80

LogMAR

-0.10

0.00

0.10

0.20

0.30

0.40

This scale is upside down from most in Chapter 5

Worse acuity

better resolution acuity

Possible causes

Decreased density of photoreceptors in fovea

(some loss of cones)

But also, you need to insure the luminance level of the chart is high enough because (remember!) resolution acuity is poorer with low retinal illuminance

Decrease in

Spatial contrast sensitivity at intermediate and high spatial frequencies

(not just cutoff high spatial frequency)

Spatial Frequency (cycles/deg)

0.5 1 2 4 8 16

ContrastSensitivity

2.5

5

10

25

50

100

250

20's

30's40's50's

70's

60's

80's

Cause is unknown

…but since acuity also changes (MAR increases – worse acuity), and the cutoff high spatial frequency is the same as grating acuity, the two may reflect the same process

Decreased temporal CSF at intermediate and high temporal frequencies

Decrease in CFF

Less accuracy in judging direction of motion.

Causes unknown

Decrease in

Sensitivity in increment threshold tasks

(Threshold goes up)

Angular Distance From Fixation (degrees)

-60 -45 -30 -15 0 15 30 45 60 75 90

Log Increment Threshold, L (Apostilbs)-4

-3

-2

-1

0

1

2

3

00.0010.010.11101001000

Backgroundluminance, L

Sensitivity is up on this graph

Age (yrs)

20 30 40 50 60 70 80

MeanSensitivity (dB)

10

20

30

400o-30o FieldFovea

30o-60o Field

Sensitivity is up on this graph

The “Hill of Vision” gradually sinks into the “Sea of Blindness” (but, not completely)

Differential Light Sensitivity

Decrease in

Useful field of view – test vision in both the central visual field and periphery using realistic complex scenes with distracting stimuli

The “useful field” decreases with age.

•Reduced speed of visual processing

•Reduced ability to divide attention

•Reduced salience of targets against background

Useful field of View

May be a predictor of accident rate

Training can increase the useful field of view

Activities of Daily Living scales

Measure how well people function

•Non visual

•Dress selves

•Bathe selves

•Visual

•Read newspaper

•Look up phone numbers

Spatial CSF relates to visual ADL performance

(active area of research to develop visual ADL tests)

Screening older drivers (psychophysics at work)

Older drivers have disproportionately more accidents and citations than middle aged drivers

Acuity tests are not a very good predictor

The useful field of view is being developed (at UAB) as a way to identify the drivers with greatest risk (visual search skills)

The Aging Visual System

It’s generally down hill, but the rate is highly variable

“If I’d known I’d live this long, I’d have taken better care of myself”

The choices we make can affect our vision later in life

For instance, smoking is a big risk factor for age-related macular degeneration