In the early months of life, the visual system is still maturing; it is not fully developed at birth (and is even less developed in the premature infant). From birth to maturity, the eye increases to three times its size at birth, and most of this growth is complete by age 3; one third of the eye's growth in diameter is in the first year of life. Some knowledge of normal visual development is necessary if abnormalities are to be noted. The following information gives indicators of normal visual development in young children from birth to three years.
In a premature infant: (depending on the extent of prematurity) The eyelids may not have fully separated; the iris may not constrict or dilate; the aqueous drainage system may not be fully functional; the choroid may lack pigment; retinal blood vessel's may be immature; optic nerve fibers may not be myelinized; there may still be a Pupillary membrane and/or a hyaloid system. Functional implications: lack of ability to control light entering the eye; visual system is not ready to function.
At birth: The irises of Caucasian infants may have a gray or bluish appearance; natural color develops as pigment forms. The eyes' pupils are not able to dilate fully yet. The curvature of the lens is nearly spherical. The retina (especially the macula) is not fully developed. The infant is moderately farsighted and has some degree of astigmatism. Functional implications: The newborn has poor fixation ability, a very limited ability to discriminate color, limited visual fields, and an estimated visual acuity of somewhere between 20/200 and 20/400.
By 1 month: The infant can follow a slowly moving black and white target intermittently to midline; he/she will blink at a light flash, may also intermittently follow faces (usually with the eyes and head both moving together). Acuity is still poor (in the 20/200 to 20/400 range), and ocular movements may often be uncoordinated. There is a preference for black and white designs, especially checkerboards and designs with angles.
By 2 months: Brief fixation occurs sporadically, although ocular movements may still be uncoordinated; there may be attention to objects up to 6' away. The infant may follow vertical movements better than horizontal , and is beginning to be aware of colors (primarily red and yellow). There is probably still a preference for black and white designs.
By 3 months: Ocular movements are coordinated most of the time; attraction is to both black and white and colored (yellow and red) targets. The infant is capable of glancing at smaller targets (as small as 1"), and is interested in faces; visual attention and visual searching begins. The infant begins to associate visual stimuli and an event (e.g., the bottle and feeding).
By 4 months: "Hand regard" occurs at about 15 weeks; there is marked interest in the infant's own hands. He/she is beginning to shift gaze, and reacts (usually smiles) to familiar faces. He/she is able to follow a visual target the size of a finger puppet past midline, and can track horizontally, vertically, and in a circle. Visual acuity may be in the 20/200 to 20/300 range.
By 5 months: The infant is able to look at (visually examine) an object in his/her own hands; ocular movement although still uncoordinated at times, is smoother. The infant is visually aware of the environment ("explores" visually), and can shift gaze from near to far easily; he/she can "study" objects visually at near point, and can converge the eyes to do so; can fixate at 3'. Eye-hand coordination (reach) is usually achieved by now.
By 6 months: Acuity is 20/200 or better, but eye movements are coordinated and smooth; vision can be used efficiently at both near point and distance. The child recognizes and differentiates faces at 6', and can reach for and grasp a visual target. Hand movements are monitored visually; has visually directed reach." May be interested in watching falling objects, and usually fixates on where the object disappears.
Between 6 and 9 months: Acuity improves rapidly (to near normal); "explores" visually (examines objects in hands visually, and watches what is going on around him/her). Can transfer objects from hand to hand, and may be interested in geometric patterns.
Between 9 months and a year: The child can visually spot a small (2-3mm) object nearby; watches faces and tries to imitate expressions; searches for hidden objects after observing the "hiding;" visually alert to new people, objects, surroundings; can differentiate between known and unfamiliar people; vision motivates and monitors movement towards a desired object.
By 1 year: Both near and distant acuities are good (in the 20/50 range); there may be some mild farsightedness, but there is ability to focus, accommodate (shift between far and near vision tasks), and the child has depth perception; he/she can discriminate between simple geometric forms (circle, triangle, square), scribbles with a crayon, and is visually interested in pictures. Vision lures the child into the environment. Can track across a 180 degree arc.
By 2 years: Myelinization of the optic nerve is completed. There is vertical (upright) orientation; all optical skills are smooth and well coordinated. Acuity is 20/20 to 20/30 (normal). The child can imitate movements, can match same objects by single properties (color, shape), arid can point to specific pictures in a book.
By 3 years: Retinal tissue is mature. The child can complete a simple formboard correctly (based on visual memory), can do simple puzzles, can draw a crude circle, and can put 1" pegs into holes.