Put Simply What is Lazy Eye (Amblyopia)?
- Amblyopia is an eye condition in which a defect in one eye prevents the eye/brain connection from fully developing that eye.
- This typically occurs before the age of 7.
- This causes the individual to suppress the defective eye.
- The suppression of one eye is typically due to something that prevents the eye from seeing well such as cataracts, refractive errors (myopia. hyperopia), eyes with a large disparity between the left and right, strabismus and double vision.
Understanding Lazy Eye
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How the Eye Works
The eyeball consists of three layers: sclera, choroid and retina.
- The sclera is the thick outer layer of the eye, 4/5th of which is white and the rest is transparent. This transparent area, known as the cornea, allows light to enter the eye and is the the first stage of refraction (bending of light rays).
- The choroid layer contains blood vessels designed to nourish the retina. The anterior (front) part is modified to form the iris. This is the coloured part of the eye, which has two sets of smooth muscles: radial and circular. The radial fibers which are responsible for dilation allow more light to enter the eye. The circular fibers which are responsible for constriction, let in less light and sharpen the image. Another modified function of the choroid layer is the cillary body muscle that surrounds the edge of the lens, connected to the lens by suspensory ligaments. In a process known as accommodation, the lens is rounded when the cillary muscle contracts and flattens when it relaxes, enabling the eye to focus on objects at different distances.
- The retina lines 2/3rd’s of the innermost layer of the eye. It contains the essential cells responsible for converting light rays into electrical signals (phototransduction) which are then sent to the brain for processing. These cells are known as photoreceptors and can be divided into rods and cones. Each eye roughly contains 6 million cones, found mostly in the centre of the retina. This central area is otherwise know as the macula and allows us to see colour and fine detail. In our periphery we have 120 million rods, which are responsible for seeing movement and dim light.
The electrical signal created by phototransduction is sent via the optic nerve to the thalamus where unnecessary information is discarded. It is then sent to the visual cortex located in the occipital lobe for initial processing, before being sent to other areas of the brain. The two separate images from each eye are not identical and are put together to create one single fused image, otherwise known as binocular vision.