lecture 3

• Eyeball


  • At birth, the eye is larger in relation to the rest of the body than is the case in children and adults
  • Axial length is 12mm(26 weeks), 16 mm (36 weeks)
  • Full term neonate: In relation to its ultimate size (reached at 7—8 years), it is comparatively short, averaging 17.3mm in antero-posterior length. This would make the eye quite hyperopic
  • By age of 3 years, mean AL reach to 21.8mm
  • Male infants have larger average AL then female(0.24 mm difference)
• Cornea


  • At 34 weeks corneal diameter will be around 8.2 mm reaching 9 mm around the 37 weeks
  • The newborn infant has a relatively large cornea (9.8 mm) that reaches adult size (12mm) by the age of 2 years
  • It is steeper than the adult cornea, and its curvature is greater at the periphery than in the center(the reverse is true in adults)
  • Corneal flattening occurs in the first few months of life and in late teens
  • average corneal power is greater in infants than in children or adults for a relatively transitory period
  • full term birth corneal power will be 51-48.5D and at 1 year it will be 43-44D that remain stable throughout childhood
• Lens


  • At birth the crystalline lens is more globular than in adulthood, and its greater refractive power (34.4 D-41D) compensates for the shortness of the eye. Then becomes about 22–23 D by age 14 years
  • The lens grows throughout life as new fibers are added to the periphery, and this causes it to flatten
  • The consistency of the lens material changes throughout life from a soft plastic like material to the glassy consistency seen in old age. This accounts for the gradual loss in power of accommodation with advancing age
• Optic nerve


  • By term, some fibers in the optic nerve near the globe begin to become myelinated, but the amount of myelin surrounding individual nerves increases dramatically during the following months and may continue to increase up to the age of 2 years
  • The optic nerve becomes fully myelinated by 4 months after birth, reaching adult levels by 2 years of age
• Iris


  • At birth there is little or no pigment on the anterior surface of the iris. The posterior pigment layer shows through the translucent tissue, usually giving the effect of a blueish or slate-gray color
  • As the pigment begins to appear on the anterior surface, the iris assumes its definitive color
  • If considerable pigment is deposited, the eyes become brown. Less pigmentation results in blue, gray, hazel, or green eyes
  • It may take 1—2 years for the pigmentary deposits to occur; in the meantime it is impossible to ascertain the ultimate color of the eyes
• Pupil


  • In the newborn, the pupil is situated slightly to the nasal side of and below the center of the cornea
  • Because of the refractive power of the cornea in the neonatal period, the pupil appears larger than it actually is
  • The apparent diameter varies between 2.5 and 5.5mm and averages about 4 mm
  • In infancy, the pupil is smaller than at birth
  • Congenital underdevelopment of the dilator muscle is common in children with congenital cataracts
  • The pupillary reflexes appear at about the fifth fetal month and are active by the sixth month
  • At about age 1 year the pupil begins to widen and it reaches its greatest diameter during adolescence
  • It again becomes smaller with advancing age
  • Myopes have larger pupils than hyperopes
  • Normal pupils are round and regular and constantly move in response to changes in lighting and upon focusing
  • Anisocoria, a slight stable and consistence difference in the size of the 2 pupils, is often a normal finding; in the absence of neurological abnormalities (physiological anisocoria), it requires no further special diagnostic consideration when both pupils function normally and react properly to changes in light
• Naso-lacrimal System


  • The fetal development of the naso-lacrimal passages begins as cords of cells that usually hollow out about the time of birth
  • Because there may normally be a few weeks' delay in duct formation, failure of tear production in the first few weeks does not necessarily indicate any difficulty; failure of the ducts to function by 6 months of age, however, needs attention
• Retina


  • The most notable difference between the infant and adult retina is the shape, size, and distribution of the cone photoreceptors
  • The cones of newborns are short, stubby, and less densely packed. Because more light passes between the cones the infant's retina is less efficient than an adult's in absorbing light
  • In addition, the cones of a infant have fat inner segments and small outer segments, they contain less visual pigment. This further reduces their ability to capture and respond to light
  • As the infant grows, the cones elongate, become more densely packed and migrate toward the center of the retina to form the fovea, the area of best acuity. These changes improve the eye's light capturing ability as well as its acuity
• Pathology of Congenital Ocular Embryology


  • Failure of regression of primitive vascular tissue at the proper stage, or failure of fusion of embryonic tissue, would lead to a defect of development, e.g., of the iris or choroid (coloboma)
  • These defects are often seen grossly as a missing wedge of iris tissue or may be seen with the ophthalmoscope as a large white band extending radially along the inner surface of the eye toward the periphery
• Congenital defects of the ocular structures


  • Developmental anomalies or dysplasia of embryonal origin such as colobomas, dermoid tumors, enophthalmos, and microphthalmos
  • Tissue reactions to intrauterine inflammation in the latter months of gestation. such as lesions of chorioretinitis similar to those seen in postnatal life and some forms of cataract
• Heredity also plays a major role in many congenital deformities (Ex. Cataract, Glaucoma, Retinitis pigmentosa)
• The most common ocular disorders of children


  • external infections of the conjunctiva and eyelids (bacterial conjunctivitis, sties, blepharitis)
  • strabismus
  • ocular foreign bodies
  • allergic reactions of the conjunctiva and eyelids
  • refractive errors (particularly myopia)
  • and congenital defects
• Since it is more difficult to elicit an accurate history of causative factors and subjective complaints in children, it is common to overlook significant ocular disorders (especially in very young children, macular degeneration… etc)
• Aside from the altered frequency of occurrence of the types of ocular disorders, the causes, manifestations, and treatment of eye disorders are about the same for children as for adults
• Visual function development in infants and children


  • At birth, the vision is poor (VA= hand movements)
  • The newborn infant will be able to look at light sources and only begin to develop eye contact with adults by around the age of 6-8 weeks
  • Soon after, the infant will be able to follow large objects which move slowly near to him
  • The child will now begin to reach objects with his/her hands especially brightly colored and larger objects
  • The eyes will begin to move more with less head movement
  • The child will also be learning to grasp with his/her hands and also watch the parent's face when being talked to
  • The child will be able to see smaller objects such as bread or rice bits or sweets
  • Interact with the parents or care givers upon an interested pictures or TV show
  • Fixate and follow objects of interest such as his favorite toy
  • Recognize people's faces and pictures
  • know the way around the house or nursery as the child begins to crawl
  • The child's vision can be estimated by watching the child grasp tiny objects in his surrounding (on the ground or food table)
  • The child now becomes interested in picture or cartoon books, and may even recognize them as representations of real objects
  • The vision can now be tested accurately using picture recognition and matching technique with Kay or Cardiff picture cards
  • All children should be screened by the age of 3 years because squints and amblyopia (lazy eye) usually manifest by this age group
• Development of Visual Capabilities


  • Infants can see at birth. They can imitate mouth opening , as opposed to tongue protrusion ,within a few hours
  • While they may not discriminate their mother's face until 2 months of age, but this is because they are inspecting the external features of the face
  • The development of visual capabilities over the first few months is a coordinated matter involving sensory and motor aspects
  • Looking at objects is very much a sensory–motor activity
  • The adult visual system can be thought of as three systems - Noticing, Moving the eyes, and Inspecting
  • We notice objects in the peripheral field of view, and move the eyes with a saccadic movement to look at them if they demand attention
  • We converge the eyes to look at nearby objects, and diverge them to look at objects far away, so that the images in the two eyes can be fused into a single perception
  • Then we use the central part of the field of view to inspect objects and analyze their form, color, and distance in relation to other objects
  • The inspection of an object involves some eye movements because images that remain stationary on the retina fade away
  • To avoid this, the eyes drift slowly across the object, interspersed with small jerks called micro-saccades
  • Fixation of one's gaze on an object is therefore an active process rather than a passive one
  • Improvement of the ability to see fine detail in an object depends on the ability to keep one's eyes tightly fixated on it
  • Improvement in binocular function goes hand-in-hand with the ability to converge or diverge one's eyes to look at the object
  • There is a cycle in the visual system: better sensory capability leads to more accurate eye movements leads to better sensory capability and so on
  • At 2 weeks of age, infants have some ability to focus their eyes on objects at different distances, and this ability increases during their first 3 months
  • The need for infants to accommodate is much less than that of adults
  • Their acuity is less than one tenth that of adults, so that they cannot detect whether an object is in or out of focus as well as an adult can
  • The fact that they do not make large accommodative efforts is due to lack of need as much as to lack of ability
  • Thus, with the exception of some astigmatism, the image that falls on the infant retina is a clear one, and the infant can make adjustments for objects at different distances
  • Therefore, as vision develops, it is not the optics of the eye ball that develop as much as it is the properties of the photoreceptors, the retina, and the central visual system