Resolving Power of the Eye..........pptx

Resolving power of eye

1. Resolving Power of the Eye Madiha Nazly Optometrist/COAVS

2. Visual Acuity Visual acuity is the resolving power of the eye It is the measure of spatial resolution of the eye, in other words an estimation of its ability to discriminate between two point. Ability to see two objects as separate. Minimum angular size of detail that can just be resolved. It is considered as the measure of form sense.

3. Vision It is the complex integration of visual perceptions i.e. Light sense Form sense Sense of contrast Color sense Derived from the latin word ‘ acuitas ’ meaning sharpness. E ye’s ability to see fine details

4. Principles Based on two theories Receptor theory Resolution theory

5. Receptor theory If the image fell on two cones separated by one unilluminated cone then points of light will be perceived as two distinct sources. In terms of length of the retinal image, two points will be seen clearly when their image size is more than 4,5 microns. (diameter of individual cone-1.5 microns). In terms of visual angle , two adjacent points seen clearly and discretely when they produce visual angle more than one minute of arc. Visual angle is the angle subtended at the nodal point of the eye by an object in the visual field.

6. Minimum angle of resolution MAR is the angular size of detail of the visual acuity letter in minutes of arc The denominator in S nellon acuity is a measure of the size of a letter read and the angle the subtend. The classic Snellon fraction is the reciprocal of minimum angle of resolution

7. Snellon’s VA VA= distance of the patient from the chart/ smallest line read by the patient

8. Each letter is designed in a square The breadth of black strokes and white spaces are equal. The breadth of line and spaces produces angle 1 minute of arc at nodal point of eye when viewed from a certain distance. Each letter subtend an angle of 5 minute of arc when viewed from certain distane .