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.
We describe three patients in whom an isolated sixth nerve palsy was the only clinical symptom or sign of multiple sclerosis (MS). Data were collected prospectively over 6 years on these three patients, who showed no other signs of brainstem dysfunction or prior symptoms; in addition. Retrospective analysis of all patients with MS and all patients with sixth nerve palsy referred to a neuro-ophthalmology service between 1982 and 1998 showed isolated sixth nerve palsy to be the presenting sign of MS in only 0.5% of these patients. MS was the cause of isolated sixth nerve palsy in 0.8% of all patients and in 1.6% of those aged 18-50 years. Although it has been previously suggested that sixth nerve palsy is a not uncommon presenting sign of MS, our results suggest it is rare.
We would like to present a case of branch retinal artery occlusion following uneventful phacoemulsification, possibly caused by sub-Tenon's anaesthesia. There were no predisposing general health problems. There are two possible mechanisms: (1) mechanical effect of the bolus anaesthetic; (2) pharmacologically mediated changes in the vascular calibre. The latter mechanism is much more probable, because of the vasoconstrictive properties of both medications used. This is the first reported case of branch retinal artery occlusion after sub-Tenon's anaesthesia with preservative-free medications.
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