Optic nerve head pit

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An optic nerve head pit is a congenital condition, but one that may be associated with degenerative complications. The pit develops as an anomalous outpouching of neuroectoderm, surrounded by a connective tissue capsule that communicates with the subarachnoid space.

Larger and more temporally located pits carry a substantial risk of non-rhegmatogenous serous retinal and macular detachment.

Symptoms

Optic nerve head pits are asymptomatic in the absence of macular retinal detachment. When this complication occurs - usually in the third or fourth decade - potential symptoms include metamorphopsia (distortion of objects), micropsia (objects appearing small) and blurred vision.

Signs

? At the optic disc, there is a pale, round or oval pit of variable size. The pit is typically discoloured it may be pale, yellowish or grey. More than 80 per cent of cases are unilateral and the optic disc is larger in the affected eye

? Visual field defects - most commonly arcuate scotomas - are present in 60 per cent of cases, particularly when neuroretinal rim tissue is affected

? If the optic disc pit is centrally located, then glaucoma is an important differential diagnosis

? When the pit is located temporally, as in around two-thirds of cases, there is a 40 to 50 per cent chance of developing serous retinal detachment at the macula. The retinal detachment appears as a smooth elevation of the retina extending from the optic disc pit towards the macula. In about 25 per cent of eyes with retinal detachment a lamellar, outer layer macular hole develops.

Prevalence

Rare (about 1 in 10,000).

Significance

May cause severe, irreversible loss of central vision.

Differential diagnosis

Central serous chorioretinopathy, other optic nerve dysplasias - Coloboma, Morning glory syndrome, Normal tension glaucoma. As with other congenital optic disc malformations, the disc diameter is larger in an optic disc pit, whereas glaucoma being an acquired condition tends to have a similar overall disc diameter in the two eyes.

See also

Retinal detachment, Macular hole.

Management

Additional investigations

With fluorescein angiography, the pit usually demonstrates early hypofluorescence and late hyperfluorescence. Scanning laser ophthalmoscopy

Laser surgery

The natural course of serous macular detachment carries a poor prognosis, due to permanent macular damage unfortunately there is little evidence that existing treatments are beneficial. Some practitioners prefer to intervene when signs of detachment first appear. Laser photocoagulation to the temporal margin of the optic disc may reduce the accumulation of subretinal fluid.

Incisional surgery

Observations in several case studies show resolution of subretinal fluid following surgery to alleviate vitreoretinal traction. Procedures including pars plana vitrectomy and intraocular gas tamponade have been employed. However, even with full resolution of retinal detachment, vision will not necessarily improve.

Prognosis

Serous retinal detachment has a poor prognosis, with over half of affected eyes having acuity of 20/100 (6/30) or worse within one year.

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Yearly review is recommended in the absence of complications. The patient may be given an Amsler grid for self-monitoring and educated regarding macular detachment symptoms.