3. The resolving power of the eye is known as visual acuity. 
    Write short notes on its physiological basis. 
Visual acuity is a measure of our ability to discriminate the finest detail: either by discriminating two parallel lines apart (Vernier acuity) or two tiny spots or stars apart (point discrimination). 

The primate and human visual system is capable of acuity of 1 min of arc or 60 cycles/degree of visual angle. One degree of visual angle is thought to cover approximately 280-300 um of retinal distance. 

The area of the retina where the cone photoreceptors are most closely packed in a more or less hexagonal array, is, of course, the fovea. So visual discrimination of 1 min of arc is about the center to center spacing of the cones of the central mosaic in the foveola. 

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