Supporting people with
aniridia and their Families
Just Diagnosed? click here
Supporting people with
aniridia and their Families
Just Diagnosed? click here
Optic Nerve HypoplasiaWhat is the optic nerve? A large collection of communication wires to the brain (optic nerve). the optic nerve develops in the 7 to 8th weeks of pregnancy. What is optic nerve hypoplasia? Hypoplasia is a medical term for underdevelopment therefore optic nerve hypoplasia means underdevelopment of the optic nerve. When the optic nerve is underdeveloped it has fewer wires than it should have connecting the visual information recieved by the retina to the brain and this means that that not all of the visual information gets to the brain. How does this affect vision? It depends upon how underdeveloped the optic nerve is. The doctor will compare the horzontal optic disc diameter to the distance between the optic nerve and Macula (a tiny point on the retina). From this the doctor will work out a ratio that can help assess the visual acuity of young children and babies. A ratio of more than 0.3 means the child will have a good visual acuity A ratio of less than 0.15 means the child will have a visual acuity better than light perception Generally speaking children with bilateral optic nerve hypoplasia do not have a good visual prognosis. However, about 10% have excellent vision. Some children will have nystagmus. The effect on the visual field may range from generalized loss of detailed vision in both central and peripheral fields (depressed visual fields) to subtle peripheral field loss. Depth perception may be poor depending on the servrity of the vision loss and it may contribute to the photophobia that people with aniridia experience. Colour perception may be reduced. How is it diagnosed?
An eye doctor, ophthalmoglist, will look though a special machine at the back of the eye. Here they will see the "head" of the optic nevre. This is where the wires going to collect together to go to the brain. From this view the opthalmoglist will take the measurements mentioned above. if the optic nerve looks small then the child has optic nerve hypoplasia. Why do people with aniridia have optic nerve hypoplasia and how does it affect them? Aniridia is a condition in which the eye is generally underdeveloped and therefore, at the back of the eye the retina and the optic nerve tend to show some degree of underdevelopment. In a recent study of 56 people with aniridia, optic nerve hypoplasia was found in roughly 10% of patients with aniridia and may occur independently or in association with foveal hypoplasia. People with aniridia tend to have nystagmus and they usually have between 20/100 and 20/200 depressed field of vision. Optic nerve hypoplasia is not a progressive condition, and it cannot be cured. However, as the childs' eye matures, there may be a slight improvement in visual funtion and nystagmus may be reduce. References Scottish Sensory Centre - Medical Information on Septo-optic Dysplasia Pediatric Visual Diagnosis Fact Sheet - OPTIC NERVE HYPOPLASIA Aniridia and optic nerve hypoplasia, McCulley TJ, Mayer K, Dahr SS, Simpson J, Holland EJ, Eye. 2004 Sep 10 |