Lecture 2 Child visual development Mutez Gharaibeh,MD Pediatric Optometry Lecture 2 Child visual development Mutez Gharaibeh,MD

Monocular devlopment . Binocular development ----- Amblyopia .

Most of eye growth occurs in first 2 -3 yrs of life . Congenital glaucoma --- Buphthalmos Adult glaucoma ---- No buphthalmos

Corneal size ↑ by ≈ 50% Retinal surface area 590 mm2----- 1250 mm2 Axial length 16.8mm-----23.6mm ( +7) Corneal power 51.2 D ----43.5D Lens power 34.4 D ---- 18.8D ( - 30D)

Refractive errors The average refractive error in children from birth to 1 year of age is about 2 diopters (D) of hyperopia . Astigmatism up to 2 D is common in children under 3 years of age. Low amounts of anisometropia are common and variable in infants.

< 3.5 yr --- usually against the rule . Studies show that 30-50 percent of infants less than 12 months of age have significant astigmatism, which declines over the first few years of life, becoming stable by approximately 2½ to 5 years of age. < 3.5 yr --- usually against the rule . >3.5 yr --- usually with the rule . With the rule against oblique

Retina Foveal region gets to be thinner ( 1000лm --- 700 лm ) by 4 yrs. Cones density/area increases by age. More peripheral retina develops faster than foveal area. X,Y,W ganglion cells.

W-type Y- type X- type properties Variable Large Medium Size Small Dendritic spread Sustained sluggish Transient brisk Sustained brisk Response Slow Fast Conduction Receptive field size LGN LGN( Magno) LGN ( Parvo) Projection Moving targets ( high grefuency flicker) Static targets ( low frequency flickers)

LGN

LGN The main difference between infants and adults is the size . Parvocellular layers reach adult size by end of 12 months. Magnocellular layers reach adult size by end of 24 months.

Visual acuity the spatial resolving capacity of the visual system . Spatial resolution= angular resolution =describes the resolving power of the eye. Resolving power is the ability of the components of an imaging device( e.g: eye) to measure the angular separation of the points in an object .

Visual acuity Visual acuity is limited by diffraction, aberrations and photoreceptor density in the eye . a number of factors also affect visual acuity such as refractive error, illumination, contrast and the location of the retina being stimulated.

Visual acuity Target detection requires only the perception of the presence or absence of an aspect of the stimuli . Landolt C and the Illiterate E are forms of detection used in visual acuity measurement in the clinic.

Visual acuity Target recognition tasks

6/6 (20/20)

logMAR

Vernier acuity Vernier acuity is the ability by a person to detect the proper alignment of two line segments

Grating acuity aspect of visual acuity involving the ability to distinguish the elements of a fine grating composed of alternating dark and light stripes or squares .

Angular acuity = Reading a letter Morphoscopic acuity =Reading a letter in a line. Crowding phenomena=

Development of visual acuity Visual acuity contrast sensitivity Birth ≈ 6/300 unknown 3 months 6/90 --- 6/60 ≈ 6/60 1 yr ≈ 6/24 ≈ 6/9 2 yrs ≈ 6/12 --- 6/9 ≈ 6/6 3 yrs ≈6/9 ---6/6 ≈ 6/6

Saccadic system Smooth pursuit system Optokinetic nystagmus

Babies are not born with all the visual abilities they need in life . The ability to focus their eyes, move them accurately, and use them together as a team must be learned . Eye and vision problems in infants can cause developmental delays.

Visual milestones Not every child is the same and some may reach certain milestones at different ages.

Birth-4 mo Up to about 3 months of age, babies' eyes do not focus on objects more than 2-3 meters from their faces. By eight weeks, babies begin to focus their eyes on the faces of a parent or other person near them. But they still cannot follow. For the first two months of life, an infant's eyes are not well coordinated , However, if an eye appears to turn in or out constantly, an evaluation is warranted. Babies should begin to follow moving objects with their eyes and reach for things at around four months of age.

5-8 months During these months, control of eye movements and eye-body coordination skills continue to improve. Depth perception is not present at birth. It is not until around the fifth month that the eyes are capable of working together to form a three-dimensional view of the world and begin to see in depth. it is generally believed that babies have good color vision by five months of age. Most babies start crawling at about 8 months old, which helps further develop eye-hand-foot-body coordination. Early walkers who did minimal crawling may not learn to use their eyes together as well as babies who crawl a lot.

9-12 months At around 9 months of age, babies begin to pull themselves up to a standing position. By 10 months of age, a baby should be able to grasp objects with thumb and forefinger. By twelve months of age, most babies will be crawling and trying to walk. Parents should encourage crawling rather than early walking to help the child develop better eye-hand coordination. Babies can now judge distances fairly well and throw things with precision.

12-24 months By two years of age, a child's eye-hand coordination and depth perception should be well developed. Children this age are highly interested in exploring their environment and in looking and listening. They recognize familiar objects and pictures in books and can scribble with pencil.

What do you need to know about child visual development 1- Summary + table 3.4 ( page 70). 2- slides.

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