Optic nerve pits are attributed to incomplete closure of the foetal fissure. This usually occurs during the first trimester of pregnancy. A more exaggerated effect of incomplete closure is a complete coloboma of the optic nerve. Optic nerve pits are also known as ‘atypical colobomas.’
Optic nerve pits vary in size, occupying from one quarter to one half of the disc diameter. The depth of the optic pit can also vary. The pit can take the form of a round or oval depression. They may appear olive-grey, yellow or white. This depression is frequently situated in the temporal or infra-temporal region of the optic disc. There is usually only one pit per optic disc, although two or three occasionally occur. Optic nerve pits are unilateral in most of the cases. Circumpapillary chorioretinal atrophy with pigmentation changes are seen in almost all cases where the pit is situated near the optic disc margin. In more than half of the cases, a cilioretinal artery can be identified arising from the periphery of the pit.
Visual acuity usually remains unaffected unless the patient develops a serous retinal detachment of the macula. These serous macular detachments are usually related to larger pits in the temporal region of the optic disc.
Although management of serous macular detachments secondary to optic pits remains controversial, recent attempts have included the use of argon and krypton laser treatment, pars plana vitrectomy with fluid-gas exchange and sponge explant procedures. Attempts to repair the macular detachment and improve vision should be considered before prolonged detachment results in irreversible degenerative changes.
Diagnosis of optic nerve pit
If the pit is not affecting vision, the patient will have no symptoms and will not complain. It is discovered on routine eye examination. Most cases are diagnosed by fundus examination using the slit lamp or indirect ophthalmoscope. If the pit affects the vision, further examination techniques may be used like fluorescein angiography of the retina or OCT.
Effect of optic nerve pit on vision
The pit itself does not affect vision and most patients remain without any symptoms for many years. About half of patients start feeling vision deterioration in their 20’s or 30’s. It is very rare for a child with optic nerve pit to get a visual problem in childhood. Defect in vision occurs due to collection of fluid under central part of the retina. Even with the right treatment, vision may not return to normal.
Treatment of optic nerve pit
There is not treatment required for optic nerve pit and there is no preventive measure to avoid the accumulation of fluid and the associated diminution of vision. Treatment only starts after the fluid accumulates. In some cases, the fluid disappears impulsively without treatment. In such cases an eye specialist may require the patient to limit activity for some time and to come for frequent follow up visits. In other cases surgery may be required to clear the fluid.