程序代写 Effect of Grouping on Lightness

Effect of Grouping on Lightness

Week 2: Anatomy of the Eye and Visual Acuity

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Brief survey of the anatomy of the eye
Visual size and visual angles
Visual acuity – its measurement and the impact of acuity reduction.

Structures of the Eye

Visual Angle

Angular Size in radians  Physical Size / Viewing Distance
Angular Size in degrees  57.3 × Angular Size in radians
= 57.3 × Physical Size / Viewing Distance
where the physical size and viewing distance must be measured in the same units (typically, mm, cm, or inches). These approximations hold when the physical size is significantly smaller than the viewing distance.

How large does your fist look at arm’s length?
Measure the size of your clenched fist, H.
With your arm extended, measure the eye-to-fist distance, d.
Use the formula to compute the visual angle A of your fist in radians.
Convert to degrees.

Three Dimensions of Vision Measurement and Loss
Low vision is usually discussed in terms of:
Reduced acuity
Reduced contrast sensitivity
Visual-field loss.

Demo of Lighthouse Distance Acuity Chart [Position student at 4 m to demonstrate designation of viewing distance, and point out the various lines on the chart as I discuss them.]

What is Visual Acuity?
Visual acuity: determines the smallest visual size (visual angles) of objects that can be recognize.
An object’s visual size is determined by its size/distance ratio.
At a fixed distance, acuity determines the smallest objects that can be recognized, such as letters on an eye chart.
For objects of a given size, acuity determines the greatest distance at which the objects can be recognized, such as the maximum distance for reading road signs.

Lighthouse Letter Acuity Chart

Acuity Ranges
Traditional standard for Normal vision – 20/20
“Normal” Vision – 20/8 – 20/40
Mild Low Vision – 20/40-20/80
Moderate Low Vision – 20/80 – 20/200
Legal Blindness (U.S.) – 20/200
Severe Low Vision 20/200 – 20/1600
“Blindness” (WHO) – < 20/400 Ultra Low Vision - < 20/1600 Light Perception (LP) Total Blindness Simulating 5 Levels of Acuity MNREAD Reading Acuity Chart Sample MNREAD data Original 20/40 20/80 20/160 20/320 20/640 Blank Page 20/320 20/640 /docProps/thumbnail.jpeg 程序代写 CS代考 加微信: powcoder QQ: 1823890830 Email: powcoder@163.com