Description
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 nonrhegmatogenous 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
(a) At the optic disc, there is a pale, round or oval pit of variable size. The pit is typically discolored; it may be pale, yellowish or grey. More than 80 % of cases are unilateral and the optic disc is larger in the affected eye.
(b) Visual field defects – most commonly arcuate scotomas – are present in 60 percent of cases, particularly when neuroretinal rim tissue is affected
(c) 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 percent 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 percent of eyes with retinal detachment a lamellar, outer layer macular hole develops.
Incidence
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 may assist in evaluating the pit configuration. Visual field assessment is indicated.
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.
Review and advice
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.
Figure 1.
Temporal optic disc pit associated with serous retinal detachment extending to the macula
Figure 2.
Scanning laser tomography map (right) showing 0.8mm deep pit extending infero-temporally to the disc rim, with associated supero-temporal visual field defect (left).
