1. Visual acuity, Visual field & Binocular vision
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อธิบายและบอกวิธีการหา visual acuity, visual field ได้
อธิบายกลไกของ binocular vision

2. Visual Acuity
Visual acuity is the degree to which the details and contours of objects are perceived, usually defined in terms of the minimum separable
Minimum separable - the shortest distance by
which 2 lines can be separated and still be
perceived as 2 lines (visual angle ~ 1 minute)
Snellen letter charts - viewed at a distance of
20 ft (6 m)

4. Factors affecting the visual acuity
Dioptric
Normal errors
Refractive errors
(myopia, hyperopia, astigmia)
Pupillary size
Compostion of light
Stimulus
Size of detail
Brightness contrast
Illumination
Exposure time

5. Neural factors Fovea centralis
- is the point where visual acuity is greatest
slender, densely packed cones
rod-free
no blood vessels & nerve fibers overlying
the receptors
“private line” to optic nerve
(cone-to-optic nerve fiber ratio = 1:1)
Periphery
cone-to-rod ratio decreases
increased convergence

6. Temporal Discrimination Capability
Critical fusion frequency
The time-resolution ability of the eye is determined by measuring the critical fusion frequency (CFF), the rate at which stimuli can be presented and still be perceived as separate stimuli.
Stimuli presented at a higher rate than the CFF are perceived as continuous stimuli.
An instantaneous flash of light (1/one million seconds) excites visual receptors as long as 1/10 – 1/5 second.
Motion picture frames/second
TV frames/second

7. Visual Fields & Binocular Vision
The visual field of each eye is the portion of the external world visible out of that eye.
The peripheral portions of the visual fields are mapped with a perimeter, and the process is referred to as perimetry.
The central parts of the visual fields of the 2 eyes coincide;
therefore anything in this portion of the field is viewed with
binocular vision.
The impulses in the 2 retinas are fused at
the cortical level.

8. Corresponding Points
= the points on the retina on which the image of an object must fall if it is to be seen binocularly as a single object.
Binocular vision adds appreciation of depth and proportion.
Diplopia
- If the image on the retina of the eye does not fall on the corresponding points, double vision (diplopia) results.

9. Left eye
Right eye