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| ARTICLES |
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| Year : 1983 | Volume
: 31
| Issue : 6 | Page : 713 |
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Differential tonometry in myopia
H Prabhakara Reddy, K Jayanthi
Sarojini Devi Eye Hospital Institute of Ophthalmology, Hyderabad, India
Correspondence Address:
H Prabhakara Reddy
Sarojini Devi Eye Hospital, Institute of Ophthalmology, Hyderabad
India
 Source of Support: None, Conflict of Interest: None  | Check |
PMID: 6676249 
How to cite this article:
Reddy H P, Jayanthi K. Differential tonometry in myopia. Indian J Ophthalmol 1983;31:713 |
In performing tonometry, we endeavour to determine the Intra-Ocular-pressure as close to the steady level i.e Po as possible. All tonometers in use today work on the principle of applying a force to the eye and measuring the deformation produced. Since tonometry involves the application of a force to the eye it is inevitably accompanied by a rise of 1.O.P. It is this articifially elevated pressure, usually termed pt, which is measured directly by the tonometer. The pressure which is of clinical interest, however, is the pressure Po which existed in the undisturbed eye before the tonometer was applied. It is important to recognise that for indentation tonometers like Schiotz tonometer, the difference between Po & Pt is large. Nevertheless the most frequently used tonometer worldwide is the Schiotz indentation tonometer despite clear evidence that the problem of ocular rigidity involved in indentation tonometry cause misleading results in the individual eye. (Hetland-Erisan 1966, Smith 1967, Leydhecker 1973). When the ocular rigidity differs slightly from normal, the error in deducing the true IOP Po may be negligible, but in a small proportion of eyes, the rigidity may be so far removed from normal that the error becomes clinically significant. It will he remembered that the general effect is that the Schiotz tonometer tends to over-estimate the Po in eyes of high rigidity and to under-estimate Po in eyes of low rigidity.
In order, to overcome this defect. Friedenwald proposed the so-called method of "DIFFERENTIAL TONOMETRY" in which a reading is taken with one weight on the Plunger and then a second reading' in taken with a different weight. By referring the nomogram Po and Ocular rigidity can be determined.
In general the problem of making a diagnosis of glaucoma in a pt. with myopia presents unusual difficulties. The low ocular rigidity in many of these eyes result in Schiotz readings within normal limits. Their true status is revealed by applanation tonometry. However because of the simplicity of the Technique and the cheapness and Portability of the Instrument Schiotz tonometer is still most frequently used all over. Differntial Tonometry used correctly can provide information which is morevaluable clinically than that given by a single reading with the schiotz Tonometer.
In this study,we compared the I.O.P. readings obtained by Differential Tonometry and Goldmanns tonometer in cases of Myopia. Results are compared and Advantages and disadvantages of Differential tonometer, and Goldmann tonometer are Highlighted.
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