City Research Online

Abstract

Automatic infra-red optometers provide now an alternative to conventional objective refracting methods for the human eye. The relative merits of streak retinoscopy, the Ophthalmetron and the Dioptron were quantitatively assessed on various clinical groups.

For a normal young population retinoscopy gives a more accurate estimate of the subjective than the Ophthalmetron. Use of a cycloplegic agent showed that the bias linked to the Ophthalmetron was due to instrumental accommodation and this was shown to be psychological in nature.

For a highly myopic and/or highly astigmatic population, retinoscopy is marginally more accurate than the Ophthalmetron, but the clinical usefulness of the latter is certain for this particular population.

For corneal graft patients the correlation between objective methods and subjective refraction is worse than for any of the other groups considered. This is thought to be due to the irregular nature of the dioptric systems encountered. The accuracy of retinoscopy and Ophthalmetron are of the same order, retinoscopy being slightly better.

For aphakic patients the accuracy of retinoscopy was established (standard deviation = 0.6 DS) for the mid equivalent sphere. It was shown that the Ophthalmetron, which only gave results in 79.03% of cases, was in these cases a more accurate estimate of subjective values than retinoscopy. On the contrary the Dioptron had no failures with a small population but gave results which were poorer than retinoscopy. The precision (repeatability) of refraction in aphakia when comparing three measurements with the Ophthalmetron to retinoscopy and subjective undertaken by three experienced optometrists was best in the former (standard deviation for Ophthalmetron = 0.1D, for subjective = 0.6D and for retinoscopy from 0.6D to 0.9D). The use of positive or negative cylinders and of streak or spot retinoscopy did not influence the accuracy obtained.

Finally the clinical usefulness of the Ophthalmetron as a means of post-operative refractive follow-up in aphakia and corneal grafting was demonstrated.

In the laboratory the tolerances for the Ophthalmetron were established: ±4° for angular movements and ±0.25 mm for transverse movements and greater than 4 mm for longitudinal movements. The incident infra-red beam on the patient's eye was shown to be slightly divergent.

Publication Type:	Thesis (Doctoral)
Subjects:	R Medicine > R Medicine (General) R Medicine > RE Ophthalmology
Departments:	School of Health & Medical Sciences > Department of Optometry & Visual Science School of Health & Medical Sciences > School of Health & Medical Sciences Doctoral Theses Doctoral Theses

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