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

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)

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)

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)

Sensitivity is up on this graph

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

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