Applanation tension and axial length of the eyeball

Abstract

A group of 37 myopes aged I8 to 72 years showed a mean applanation tension of I 5 49 mm. Hg (S.D. 2.8I) which was significantly higher than the mean of 13.9I mm. Hg (S.D. 2 28) in a group of 22 hypermetropes. The mean of 35 emmetropes was I4-74 mm. Hg (S.D. 2.42), i.e. nicely between the other two groups; this mean did not differ significantly from the other two. There was a statistically significant positive correlation between ocular tension and axial length, i.e. the higher the tension the greater the axial length. The group used for this study comprised 75 persons aged 18 to 27 years of the total of 94 mentioned in the preceding paragraph. Although males had a significantly higher tension than females, they also had significantly larger axial lengths; when a series of male: female pairs was chosen so that each pair had as nearly the same axial length as possible, the differences between the means of the tensions became very small (insignificant), i.e. if the groups were controlled for axial length the sex difference in tension almost disappeared. These findings are consistent with the recorded statistics which suggest that myopia is more common among patients with open-angle glaucoma than among normal individuals. Two possible explanations are immediately obvious: EITHER raised tension is an important factor in producing a large axial length OR the raised tension is produced by a large axial length. However, other common bases for our observations may exist.