Traction centered nasal to the optic nerve head in high myopic observers

Abstract

Measuring the Stiles–Crawford effect of the first kind (SCE-1), we determined effects of tractional strains caused by serial Opto-Kinetic Nystagmus (OKN) stimuli in myopic observers (near-sighted or short-sighted) just nasal to the optic disc. Responses were recorded in high myopes with and without myopic supertraction and in low myopes. SCE-1 was measured before, just after, and following recovery from serial OKN stimuli at 22^○ Temporal Visual Field (TVF). Previously, this site was identified as near the locus of greatest retinal traction in high myopic observers. Testing was photopic and within the linear portion of the Weber function. A modest increase was found in measured SCE-1 thresholds (= sensitivity reduced) immediately after serial OKN stimuli. SCE-1 functions were flatter; their peaks were transiently altered, and shifted in the opposite direction to OKN-induced saccades. Recovery occurred within a few minutes. Transients in photoreceptor alignments and sensitivity (triggered by OKN-return saccadic eye movements) occurred near 22^○ TVF in the nasal retina in all subjects measured. Differences existed between short and longer-term photoreceptor alignments.

Keywords:

• myopia [low myopia and high myopia]
• retinal traction [retinal receptor alignment, nasal myopic super-traction of the retina and choroid]
• Stiles–Crawford effect of the first kind (SCE-1)
• Opto-Kinetic Nystagmus (OKN) [serial stimuli, saccadic eye movements, saccadic suppression]
• horizontal raphé

Acknowledgements

The authors would like to express their sincere appreciation to the dedicated subjects and assistants participating in this study! And the authors thank Professors Gerald Westheimer and Clifton Schor of the University of California at Berkeley for their contributions to both analyses and interpretations of data. We also thank Professor Vasudevan Lakshminarayanan of the University of Waterloo, Waterloo, Ontario, Canada, for commenting on statistical issues encountered.

This research was supported (1) by the New Del Amo Research Program (co-sponsored by Complutense University of of Madrid, Spain, and the University of California, Systemwide); (2) by a Committee on Research, U.C. Berkeley Faculty Research Grant, (3) by a kind donation from the Branna and Irving Sisenwein Research Foundation, and (4) by a Howard Hughes Fellows Grant.

Notes

Notes

1. The important Graefe Saemisch citation mentioned in 7, cannot be found. The pertinent Apple and Raab illustrations in this edition of their book are of special interest. These figures include reference to the work of Prof. Weiss who was active in myopia research in the late nineteenth century. These were reproduced in Figure 7 in 5. The source of these illustrations is not known by Prof. Apple.

2. Holst and Mittelstaedt 33 refer to the interaction of visual and oculomotor function. This research involves the principal of re-afference which predicts modification of sensory inputs by means of feedback paths from motor to sensory areas. Such a notion led to Sperry's re-afferent mechanism hypothesis 48. Essentially, normal motor activity results in a corollary discharge that somehow provides for constancy of the observed sensory input during eye movement. This discharge basically ‘cancels’ the disturbance of perceived sensory input as the image moves over the retina during eye movement. Stark 49 discusses the intermittency-operator principle. Experiments by Young and Stark 50 demonstrated that the visual system samples sensory inputs intermittently instead of at all times. In particular, the sampling occurs at discrete intervals of no more than 200 ms. There also exists a cessation of activity for a specified period of time. Since change in threshold could be linked to sampling, the intermittency operator offers a possible explanation to saccadic suppression.