**1. Introduction**

#### **1.1 Growth and development of child's eye**

The growth and development of eye harbors many challenging anatomical and physiological alterations starting from the intrauterine life until the early puberty. After the early puberty, the axial length of eye, which is defined as the anterior posterior diameter of the eye, remains unaltered in healthy subjects. However, the refractive status of the eye may still change in adults due to aging processes. The eye development starts in the 3-week embryo, from the optic vesicles. The eye is an organ which derives from all three of the germ layers (ectoderm, endoderm and mesoderm). The initial 3 years of life is the critical period for eye development, and rapid increase in dimensions of the organ takes place in these years. Clear vision is mandatory for the development of visual cortex in this critical period. It is accepted that normal adult visual capacity develops at 3 years of age (Fredrick, 2004).

The coordinated growth of eye's refractive components to reach a plano refraction is called emmetropization. If any failure happens in this process, refractive errors develop. The axial length is either too short, causing hypermetropia, or too long, causing myopia. Astigmatism is due to abnormal shapes in cornea. Very high degrees of hypermetropia (>5D) is not normal in newborns. The cornea and lens may flatten normally within years, but the axial length often pauses behind. This causes permanent hyperopia, which is called nanophthalmos. Generally, eyes with hyperopia of greater than 5 diopters have little chance of emmetropization (Mutti, 1992).

All anatomical alterations occur in order to achieve emmetropization. The corneal diameter at birth is about 9.5-10.5 mm. The average adult size is 12 mm. The corneal refractive power is 52 diopters at birth and 42-44 diopters in adulthood. Axial length is 17 mm at birth. It enlarges to 20 mm by the end of 12 months with continued rapid growth until 2 years old, then a slow increase to 24 mm by adulthood. The most rapid eye growth occurs within the first two years. At birth the power of the crystalline lens is 34 diopters. By 6 months of age power averages 28 diopters. By the adulthood the lens power reaches about 20 diopters. As cornea, lens, and axial length grow and change rapidly over the first months and years of life, the harmonization between these three components become crucial.

Pediatric Ophthalmology / Eye and Disorders 5

It results from failure of the embryonic fissure to close along the inferonasal side of the optic cup during embryogenesis. It is frequently associated with microphthalmia. The visual

It occurs sporadically and unilaterally in full-term health infants. The affected eye is microphthalmic with a shallow anterior chamber. A vascularized membrane behind the lens is typical. If the eye is not severely microphthalmic, surgical intervention may have a good

The optic nerve is approximately 50 mm long from the globe to the chiasm. It can be subdivided into four segments: Intraocular (optic disc, optic nerve head), intraorbital, intracanalicular and intracranial segment. Optic nerve is surrounded by the vascular pia, arachnoid and dura mater. The subarachnoid space is continuous with the cerebral subarachnoid space and contains the cerebrospinal fluid. The optic nerve carries approximately 1.2 million afferent nerve fibres which originate in the retinal ganglion cells

Common congenital optic disc anomalies are present as follows: Tilted disc, optic disc pit, optic disc drusen (hyaline bodies), optic disc coloboma, morning glory anomaly, hypoplastic optic nerve and myelinated nerve fibres (Nicholson et al., 2011). Optic disc drusen is a common anomaly with a prevalence of 0.3% of the population. In buried drusen which are the most commonly encountered type, they mimic papilloedema. Exposed optic disc drusen are rare types and more easily diagnosed. They are usually innocent, but rarely may lead to visual field defects or optic disc neovascularisation. Ultrasound is important for the differential diagnosis by showing calcific deposits

Optic neuritis is an inflammatory, infective or demyelinating process affecting the optic nerve. It can be classified both ophthalmoscopically and etiologically as follows. Papillitis is characterized by hyperemia and edema of the optic disc, associated with peripapillary flame-shaped hemorrhages. Neuroretinitis is characterized by papillitis in association with inflammation of the retinal nerve fibre layer and a macular star. The optic nerve head is normal in retrobulbar neuritis, because the optic nerve head is not involved. Optic neuritis may be seen due to demyelinating disease, parainfectious, infectious such as sinus-related, or associated with cat-scratch fever, syphilis, Lyme disease, cryptococcal meningitis and non-infectious such as sarcoidosis, systemic lupus erythematosus, polyarteritis nodosa and

Papilloedema is swelling of the optic nerve head secondary to raised intracranial pressure. It is nearly always bilateral, although it may be asymmetrical. Systemic findings such as headaches, deterioration of consciousness, nausea and vomiting, may be seen in patients with papilloedema. Transient obscurations lasting a few seconds are frequent in

prognosis is linked to the degree of optic nerve and macular involvement.

**2.5 Persistant fetal vasculature (persistant hyperplastic primary vitreus)** 

**2.4 Colobomas** 

prognosis (Levin, 2003).

(Kanski 2011).

**3. Optic nerve disease in children** 

associated with drusen (Kanski 2011).

other vasculitides (Dale et al., 2009).

Normal infant eyes are 2 diopters hyperopic. This increases slightly to around age 7, then decreases to age 9-12 years when emmetropia is reached. Normal eyes have diminutive refractive changes after 13 years (Mutti, 1992).
