Letters : July 21

Binocular vison

I write with reference to the article Binocular vision - a different angle, by Tony Nixon, (July 14 - 2006). The third paragraph states that 'Dowley suggests a strong binocular adaptive process because of the statistically high numbers of heterophoric subjects'.

In fact my article relates to the higher than expected number of orthophoric subjects (not heterophoric subjects). There is a statistically significantly higher incidence of horizontal distance orthophoria than random chance would predict. The frequency distribution of distance horizontal heterophoria is significantly not normally distributed, many other physical properties such as anterior chamber depth and corneal radius show the characteristic bell-shaped frequency curve of a normal distribution. Longer periods of monocular occlusion appear to reduce the orthophorisation effect and the frequency distribution of distance heterophoria becomes more normally distributed.