No abstract

The disc-macula distance to disc diameter ratio (DM:DD ratio) has been advocated as a method of supporting the diagnosis of optic nerve hypoplasia. A DM:DD ratio of 3.00 has been claimed to be a satisfactory threshold value for this purpose. This study has critically evaluated the above claim and found a value of 3.00 to be too low. The threshold DM:DD ratio values for the diagnosis of unequivocal ONH for an adult population, 5 and 2 years of age were found to be respectively 4.20, 3.93 and 3.70, the values for the diagnosis of mild ONH being 3.68, 3.44 and 3.23. Lower computed values reduce the predictive power. The method of computation of the DM:DD ratio was modified to abolish potential error due to disc rotation and foveal displacement. In an adult population, there was no correlation between the DM:DD ratio and amblyopia or disc ovalness. There was a trend of increasing DM:DD ratio towards myopia and decreasing DM:DD ratio towards hypermetropia; the DM:DD ratio may therefore be falsely high in high myopia. DM:DD ratio values below threshold should therefore be interpreted with care until formal optic disc biometry can be performed.

Orthoptic exercises are an effective means of reducing symptoms in patients with convergence insufficiency and decompensating exophoria, and appear to target the proximal and fusional components of convergence. Their role in esophoria is unclear and needs further study.

Our ability to determine the position of targets in surrounding visual space (spatial localisation) is an important aspect of visual function and requires the integration of both visual (ie retinal) and non-visual (ie extraretinal) information. Afferent signals derived from extraocular muscle proprioceptors are though to contribute to this extraretinal information. However, this has proved to be a contentious issue. This article considers the role of extraocular muscle proprioception in spatial localisation in greater detail by discussing the evidence supporting this viewpoint. This is obtained from two main sources: firstly observations in patients in whom the proprioceptive input has been disrupted either pathologically or surgically, and secondly experimental studies in normal subjects in whom the proprioceptive input has been manipulated. The review concludes by emphasising that whilst proprioception is not the predominant source of extraretinal information that helps us determine visual direction, it is still likely to be a contributory factor.