Optic Pits (also known as optic nerve pits, optic disc pits, or less commonly optic holes) are congenital defects presumably arising from the failure of fetal fissure closure in embryogenesis.
Optic Disc Pits (ODP) were first described in 1882 by Wiethe in a 62 year old female. Since that time, they have typically been an incidental finding on routine dilated fundus exam. Rarely, they may cause visual field defects or macular changes.
An ODP usually presents itself as a unilateral, solitary, ovoid, grey-white excavation of the optic disc most commonly in the inferotemporal quadrant of the nerve head. 15% of ODP’s are thought to occur bilaterally. The size of the pit can occupy 1/8 -1/4 of the size of the disc.Depending on the optic disc size and location, they may cause arcuate field defects or enlarged blind spot. Visual acuity is typically not affected unless macular involvement is present, either by a serous retinal detachment, retinal schisis or cystoid macular edema. Patients with optic disc pit maculopathy initially notice a drop in visual acuity to around 20/70 in the affected eye.
Epidemiology and risk factors
Optic nerve pits are a rare entity. In a study by Reis in 1908, the frequency of this anomaly was estimated to be 1 out of 11,000 people. In a study by Wang el al, the prevalence was found to be 0.1%.  Of those with ODP, 25-75% experience visual symptoms . They are thought to occur sporadically with no known risk factors in particular. Men and women are affected equally.
Etiology and pathophysiology
Optic pits are thought to be a result of incomplete closure of the superior edge of the embryonic fissure. This has been the subject of some debate in the literature. The mechanisms of subretinal fluid accumulation in optic disc pit maculopathy are not well understood. It has been postulated that the fluid may arise from one of several sources; the vitreous cavity, cerebrospinal fluid (CSF) , the surrounding orbital space or dural leaking vessels at the base of the pit .
As for the theory suggesting the fluid arising from vitreous cavity, pre-existing vitreous traction on the macula and the optic disc is thought to play a role in the development of negative pressure with subsequent entrance of fluid through the ODP into the submacular space. Whereas, the theory of CSF leaking into the macular schisis or subretinal space is thought to be from a direct communication of the subarachnoid space through the ODP that transmits fluid into the intra- and subretinal space. 
On microscopic examination, there is usually herniation of the surrounding dysplastic retina and fibrous tissue into the meninges (subarachnoid space) and adjacent optic nerve through a defect in the lamina cribrosa.
Patients are generally asymptomatic and findings are usually incidentally found on routine exam. However, patients may complain of metamophopsia, micropsia, blurred vision, or a noticeable blind spot if the optic pit is associated with a serous retinal detachment.
Optic pits are generally found inferotemporally within the nerve, however up to one-third are central. They appear as a round or oval depression that differs in color from the surrounding disc (grey, yellow or black). The color variation depends on the amount and location of the glial tissue in the pit. There may associated macular edema, serous macular detachment; schisis or pigmentary changes within the macula.
A pit can be seen with direct or indirect ophthalmoscopy. For detailed evaluation, slit lamp biomicroscopic binocular examination should be performed.
Shallow serous macular detachments can be seen in upto three-fourths of eyes with inferotemporal pits. They usually become symptomatic in the 3rd or 4th decade of life though reports in children have been described.
Due to the incidental nature of this disc anomaly, investigations are usually done to diagnose, and to detect complications. Sub-retinal fluid, or macular schisis are complications that can be detected with a macular optical coherence tomography (OCT). Moreover, investigations are used to monitor for the success of treatment. Serial OCTs of the retinal nerve fiber layer along with serial Humphrey visual fields are beneficial to differentiate between ODP and other progressive optic neuropathies such as glaucoma. ODP can present with visual field deficits such as arcuate scotoma, central scotoma or an enlarged blind spot.
Fluorescein Angiography is not particularly useful in diagnosing optic pits however it may be helpful in eliminating other diseases in the differential of serous detachment.
An Amsler grid can be used to monitor the onset of macular involvement of an optic pit with a serous detachment.
DDx of Optic disc pits includes other congenital optic disc anomalies (optic disc coloboma, morning glory anomaly, hypoplastic disc or tilted discs), scleral crescent, circumpapillary staphyloma, and glaucomatous disc cupping.
DDx of optic nerve pit maculopathy include idiopathic central serous retinopathy, and subretinal neovascular membrane
Management and treatment
The first treatment modality is observation especially if there is no macular involvement. The patient is made aware of his condition and counselled with regards to the possibility of vision loss. Should the macula be affected, the treatment options include the following:
- laser photocoagulation: the objective of treatment includes repair of a serous detachment if occurred as a complication of an optic nerve pit. The technique includes laser application temporal to the disc area to create a barrier for fluid not to enter the macula. Laser photocoagulation therapy has not had much success in most studies, patients treated did not notice improvement, in fact some reported more visual disturbance after the treatment. 
- Surgical options: most commonly, a pars plana vitrectomy (PPV) is performed, with or without internal limiting membrane peel, with or without endolaser, and gas tamponade. The success of this method is based on the theory of vitreous traction leading to formation of fluid (discussed earlier). Studies have shown promising long-term results in both retinal re-attachments (50-95% of patients) and visual improvement(>50% of patients). 
A emerging surgical technique for managing ODP’s is PPV combined with inverted ILM flap to cover the optic disc and the ODP. This technique has shown promising results however evidence remains low due to the limited studies. 
There are studies that reported high success rates with injecting gas tamponade with or without barrier laser at the temporal disc edge. There was 50-75% fluid resolution and significant vision improvement, however there was a need for re-injection of gas frequently due to recurrence. 
Macular buckle is an option of treatment to promote reattachment of the macula via ab externo compression when detachment involves the macula. This procedure is considered technically challenging despite the good anatomical and visual outcomes hence it is not widely applied. 
Performing inner retinal fenestrations to create passage for the fluid to travel to the vitreous have been reported, showing fluid resolution in 95%, and vision improvement in 56%. Controlled active aspiration of the intraretinal fluid using a 38 gauge cannula for treatment of foveoschisis has been recently described.
The presence of an optic disc pit has good to poor prognosis depending on clinical findings and complications. Isolated optic pits have an excellent prognosis and usually have no sequelae. Should a patient develop optic disc maculopathy, 80% will progress to a visual acuity of 20/200 or worse. Favorable anatomic and functional results have been reported after surgery with an 87% success rate reported recently in the literature.
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