Nasal myopic super-traction (or super-involute) of the optic nerve head

Abstract

Related recent studies are brought together; 38% of high myopes with corrections = −5.00 D or greater exhibit separation and displacement of retina (less nerve fibre layer) and choroid from moorings on the nasal optic nerve, and the displaced tissues move onto/over the disc. This is termed ‘nasal myopic super-traction of the optic nerve head'. Increasing prevalence of myopia (particularly in East and Southeast Asia), make understanding this anomaly important! In affected subjects, OCT proved valuable. Evidence is presented of disc-related separation of retina and choroid, less nerve fibre layer. We measured vision, kinetic/static thresholds, and Stiles–Crawford I on the disc. Transient alterations in sensitivity and photoreceptor orientations were found and associated with saccades or serial OKN-induced traction. Given presence of visual functions on the disc, blood supply and neural connectivity were inferred (partially) intact. Is this a strain-relieving mechanism, or a precursor to further degenerative changes in affected myopes?

Acknowledgements

The author would like to acknowledge contributions by the following: A. Chang, A. Chau, S. S. Choi, J. Duncan, S. Koshy, V. Lakshminarayanan, W. Lam, D.-A. Le (now Yang), J. Lee, D. Ling, M. Kono (Menz), M. Nadadur, J. Seu, D. Schwartz, G. Westheimer. The authors expresses his appreciation to Professor Baldur Gloor, Zurich, for providing him with a copy of the Elschnig document. This research has been supported in part by NIH National Institute on Aging Grant # K07-AG 19145, and in part by a Faculty Research Grant Award from the University of California at Berkeley Committee on Research.

Notes

†At the time these records were taken, the Nidek MP-1, as then constituted, required two separate registrations of the retina for each final or composite test record, and these two registrations were each completed at different times (the head might have moved, observer fixation could have been altered, the eye rotated, etc.) For each of the two separate registration tasks, a pair of two different individual vascular-crossing-points were chosen as reference loci. We were assured by the Chief Design Engineer of the Nidek MP-1, that since then, this problem has been resolved, but this was an issue for us at the time these tests were conducted. This was verified by Nidek personnel present during tests conducted in our laboratory. Later, we utilized the simple trick shown in figure 3(a) as a means of relating the two different pairs of registration markers, one to the other. That is, we marked the centre of the optic nerve in two dimensions. At the centre of the disc, we did not normally expect to detect a visual response. A somewhat better approach would have been to employ a second reference point on the disc in order to determine if there was also a modest rotational error encountered when combining the two separate pairs of registrations and associated records 6, 19.