Coloboma is a congenital eye defect, which is represented by missing pieces of tissue (gaps or notches) in eye structures.
The eye consist of several protective layers and cavities. The outer layer consists of the sclera and the cornea. The front part of the sclera is covered by a transparent membrane called conjunctiva, involved in protecting the eyes and lining the inside of the eyelids. The cornea is a dome-shaped structure in the front of the eye that encloses the anterior chamber of the eye. It is transparent, allowing light to enter the eye, and along with the lens helps focus and direct light onto the retina.
The middle layer of the eye includes the iris, the ciliary body, the lens and the choroid. The iris gives a person’s distinct eye colour, controls the size of the pupil and hence the amount of light entering the eye. It separates the anterior and posterior chambers in the front part of the eye. These chambers contain the aqueous humour, which is important in nourishing the lens and cornea. The lens is a shear, flexible structure, which changes its shape and hence participate in focusing one’s vision on close or distant objects. The vitreous humor is a jelly-like substance that fills the back portion of the eye. It has a structural function and is involved in maintaining the eye’s shape, but also helps transmitting the light to the retina. The choroid is a membrane found between the sclera and the retina. It lines the back of the eye and is rich in blood vessels. It is highly pigmented in order to absorb light and prevent scattering.
The inner layer- the retina lines the inside of the back part of the eye and is the light-sensitive part. It is rich in photoreceptor cells and each photoreceptor is linked to a nerve fiber. Nerve fibers form the retina converge at the back of the eye to form the optic nerve. The spot where the optic nerve emerges is called the optic disc, but is also known as the blind spot. Once a image is detected by the photoreceptors, the information is converted to nerve impulses that are sent to the brain via the optic nerve. (1)
Colobomas may be present in several parts of the eye, including the iris; the retina; and often in the choroid or the optic nerve. They might be found unilaterally or bilaterally and depending on their size and location have different effects on vision. Colobomas in the iris, result in a “keyhole” appearance on the pupil and normally do not affect a person’s vision severely such as vision loss. Colobomas involving the retina result in vision loss in specific parts of the visual field, generally the upper part. Those affecting the optic nerve or large parts of the retina result in lowered vision, which cannot be corrected with glasses or contact lenses. (2)
The eye is derived from the neuroectoderm from which arise the retina proper and its associated pigment cell layer. The mesoderm of the head region produces the corneoscleral and uveal tunics and the surface ectoderm...