1. Dr Unnikrishnan Nair AIOS 10193
Tomographic Evaluation of Optic Nerve Head Pits by Spectral Domain OCT FP 694/ E Poster No 243
Dr Unnikrishnan Nair
AIOS 10193

2. Aim & Methodology
To analyse the various clinical and tomographic features like the position and nature of the pit, associated schisis , glial components over the disc , presence of SRF and PVD and extent of foveal involvement in a series of 13 patients with ONH pits
5 Line raster , Macular Cube 512 X 128 of the Carl Zeiss Cirus HD OCT were used to assess the tomographic features

3. Clinical appearance of ONH Pits
Asymptomatic Pit
Pit with resolved fluid and
Extensive RPE atrophy
Pit with Schisis & RD

4. Tomographic features evaluated
Pit communication with schisis
Pit communication with vitreous
Pit communication into substance of ONH
Schisis
SRF
Glial tissue over disc
Cloquets canal remnants
Presence or absence of PVD
IS OS loss at fovea

5. Pit communication with schisis
Communication of pit with schisis
Pit communication with Vitreous and Subarachnoid space
Communication of pit between VC & SAS
Schisis
Pit edge

6. Diaphanous membrane/glial tissue
over pit
Break in diaphanous membrane
Cloquet Canal Remnants originating from depth of cup

7. Schisis & SRF Schisis SRF SRF Glial Tissue over pit
Communication of pit with schisis
Traction on glial tissue supposedly keeping communication between schisis open
Glial Tissue in cup

8. Tomographic features Communication of pit with schisis
Communication between SAS and Vitreous cavity through Pit
11/13
Schisis
10/13
Subretinal Fluid
5/13
Glial remnants
9/ 13
Traction at Disc
7/9 with glial tissue on disc
Cloquets remnants
8/13
No PVD
No PVD in schisis
9/10

9. Pathogenesis
Congenital pits of the optic nerve head result from an imperfect closure of the superior edge of the embryonic fissure. An unequal growth on both sides causes a delayed closure of the fissure at approximately 5 weeks of gestation.
The outgrowth of axons from certain ganglion cells may be incomplete so that the primitive epithelial papilla is built up with aberrant nerve fibres.
These anomalous papillomacular nerve fibre bundles may be less resistant, predisposing this sector to spontaneous schisis-like retinal detachments during later life

10. Mechanism causing optic disc pit maculopathy
It has been considered to be vitreous traction on the optic disc pit
A reservoir for the fluid from the subarachnoid space might be the vitreous cavity with an egress into it provided by some retinal fenestration near the optic nerve head
Egress into the Schisis space is considered to be due to traction at the optic nerve edge redirecting fluid intraretinally.

11. Comparative studies
Postel et al described a hole or tear in the diaphanous tissue overlying the optic pit in all of their seven cases
Akiba et al noted a residual Cloquet's canal moving in concert with a pulsating translucent membrane over the optic disc pit to cause anterior-posterior vitreous traction. The glial tissue might have developed after continuous vitreous traction of the vitreous strand attached to the optic disc pit
Bonnet et al reported that 25 eyes with a macular detachment associated with an optic disc pit did not have a PVD
Bonnet M. Serous macular detachment associated with optic nerve pits. Graefes Arch Clin Exp Ophthalmol 1991;229(6):526–532..
Akiba J, Kakehashi A, Hikichi T, Trempe CL. Vitreous findings in cases of optic nerve pits and serous macular detachment. Am J Ophthalmol Jul 15;116(1):38–41

12. Conclusion
The following features have been noted and may explain the reason for pits developing schisis and RD
Communication between a schisis cavity or subretinal space and the optic nerve pit
Cystic degeneration and schisis
A direct communication between the subretinal space and vitreous cavity
Glial tissue with traction and absence of PVD