[Comparing applanation and impression tonometry in Central African Bantu people]

Glaucoma is the main reason for irreversible blindness in the Central African population. Because of the high prevalence, the rapid progression and the limited possibilities of diagnosis and treatment in Africa, glaucoma leads more often to blindness, compared with other parts of the world. The irreversible character of the glaucoma makes it necessary to recognise this disease as soon as possible. Beside the appearance of the optic nerve and visual field defects, tonometry is considered as an essential part of the diagnosis of glaucoma. This study compares the Shiotz tonometer with applanation tonometry to find out whether the Shiotz tonometer presents similar results in the African population.

In the time between October 2001 and July 2002 in the Democratic Republic of Congo 2020 eyes of 1027 persons were examined. Beside other ophthalmological examinations the intraocular pressure were taken by applanation (Perkins tonometer) and impression tonometry (Shiotz tonometer).

A difference of more than 2 mmHg between the two methods was found in 26.5 % of the examined eyes. Among the first 1000 eyes this difference was found in 40 % of the eyes, while among the second part of the examined eyes only in 13.2 % did a difference appear. Both methods showed a good correlation with k = 0.96 (p < 0.01). For short- or long-sighted eyes, a difference between both methods was found more often than for normal eyes. Among the long-sighted eyes the impression tonometry found higher values for the intraocular pressure more often than among the short-sighted eyes. But altogether the applanation tonometry showed higher values more often for short- as well as for long-sighted eyes. There were no correlations between the age of the examined persons and the difference between the two methods.

Altogether it can be said that for screening impression tonometry shows a satisfactory correlation with applanation tonometry in the hands of a well-trained ophthalmologist, who has done at least 1000 examinations. Differences between the two methods are mainly found for long- or short-sighted eyes.