Critical period of development of fixation reflex is
A. i.e. 2-4 months Unilateral cataract in children should be operated early in life because the critical period for development of fixation reflex is between 2" & 4th months of age.Q Age Visual Development At Bih * * * * Eye appear to move randomly & there is no central fixation Fovea is not fully developed & visual acuity is roughly 6/60. The retina is almost fully developed at bih, apa from macula which fuher develops after bih till 4-6 months of ageQ Myelination of optic nerve begins in the 7th month in utero & reaches lamina cribrosaQ(ie is completed) * Hypermetropia of +2 to +3D(2 * Orbit is more divergent (500)Q as compared to adult (450) . * A-P diameter of eyeball is 16.5 mmQ (70% of adult size which is attained by 7-8 years) * Corneal diameter is 10 mm.Q Adult size 11.7 mm is attained by 2 yrs. of age * The anterior chamber is shallower, the angle deep & the lens is more spherical as compared to the adult eye. 6 weeks (11/2 months) * Fixation reflex first becomes apparent and eye can follow bright light for a sho distance 2-4 months * Critical period for development of fixation reflexQ 4-6 months * Refixation reflex develops firmly * Macula differentiates 6-8 months * Depth perception stas developingQ 6 years * Fovea develops completely * Full visual acuity of 6/6 attained If visual developmental process is interrupted during this period by any means (eg. high anisometropia, congenital cataract) it results in amblyopia which becomes irreversible after few years. If the stimulus deprivation occurs bilaterally & severe by the age of 6 months it results in pendular nystagmus on attempted fixation. PAX6 is the master gene for eye development. Binocular Vision Psycho-optical Reflex Fusion Reflex Fixation & Refixation Reflex When a normal individual fixes * Retinal areas which coordinate visually in the Since the most accurate his visual attention on an object occipital coex so that such an object is seen vision is attained by fovea of regard, the image is formed on with both eyes as single object are k/a it is necessary that the eyes the fovea of both the eyes corresponding points. The most impoant pair be rapidly oriented so that separately, but the individual of which is foveae. Nasal half of one retina image of an object of perceives a single image. This corresponds to temporal half of other retina in interest falls upon them or state is called Binocular Single occipital coex. that of a moving object vision. It is a conditional reflex * Points on two retinae which are not retained on them. This which is not present since bih corresponding points in this sense of term are ascendancy of fovea is but is acquired during 1., 6 called disparate points and if object forms its maintained by Fixation monthsQ and is completed during retinal images on these, it will be seen double Reflex first few years. (Psycho-optical (binocular diplopia). If disparity is slight there reflex) is tendency to move the eyes so that images may be fused by means of Fusion Reflex
2-4 months of age
6-8 months of age
2 years
3 years