|Year : 1966 | Volume
| Issue : 1 | Page : 13-16
Intra-ocular tension in normal eye
HG Badlani, BD Telang
Glaucoma Clinic, K. B. Haji Bachooalli Eye Hospital, Parel, Bombay, India
|Date of Web Publication||12-Jan-2008|
H G Badlani
Glaucoma Clinic, K. B. Haji Bachooalli Eye Hospital, Parel, Bombay
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Badlani H G, Telang B D. Intra-ocular tension in normal eye. Indian J Ophthalmol 1966;14:13-6
The normal intra-ocular pressure in man may be considered to be the statistical average pressure which normal eyes have been found to tolerate over a period of time without damage to their intergrity. Since the introduction of tonometer there have been number of investigations to record the intraocular tension of the normal healthy eyes. In clinical practice intraocular pressure cannot be measured directly as such but indirectly through the state of tension of the tunics of the eye ball. This indirect deduction often leads to many variaions which cannot be always controlled. There has been a constant search to improvise the methods of recording intraocular tension so as to minimize the errors due to many variable factors.
Schiotz indentation tonometer has remaind the most popular instrument for recording intraocular tension. Since its introduction Schiotz himself devised several scales of increasing accuracy (1905, 1909 and 1924). These were further modified by Friedenwald (1948, 1955, 1957). The calibration scale used nowdays is based on the use of the applanation tonometer of Goldman which is considered as the most accurate and near ideal tonometer so far. It is interesting to note the various phases through which these studies have been carried. (Duke-Elder 1962). The average normal intraocular pressure according to 1948 Schiotz ranged from 15 - 30 mmHg averaging 20 - 25 mmHg and somewhat less for the same tonometer when 1954 calibration is used. With the subsequent calibration of 1955 (and 1957). Friedenwald stated that the 1948 calibration scales of Schiotz and McLean are too high - the average pressure was given between 18-19 mmHg rather than 22-24 mmHg as believed by Schiotz and 27 - 28 mmHg as held by McLean. (Saul-Sugar1951). Before the standardization of the tonometer was accomplished by the Committee of Standardization of Tonometers set up by the American Academy of Ophthalmology and Otolaryngology, it was discovered that many of the tonometers in common use were practically valueless, since they were of non-standard specifications. Peter C. Kronfeld (1954) has given a table of the range variation of intra-ocular tension in the normal healthy eyes as determined by Ricci, Sugar, Stine and Bloomfield [Table - 1]. The wide variations among the different authors is probably due to different samples of population examined and also because of the lack of uniformity that existed from instrument to instrument. These difficulties have been greatly overcome after the Standardization committee was set up which first reported in 1949 and then in 1954. In recent years the most extensive study has been carried out by Leydhekar (Davson - 1962) who has examined 13801 healthy eyes with the Schiotz tonometer. According to his studies the greatest probability curve occurs at 16 mmHg. Leydhekar also suggests that 95.5% of all healthy eyes have an intra-ocular tension within the range- 10.5 to 20.5 mmHg. Between the ages of 10 - 70 years and between two sexes no significant difference exists. According to Adler (1965) the range of intraocular tension in the normal healthy eyes extends from 10 to 22mmHg. and points out that this wide range makes it difficult to determine the physiological limit for a particular person. Becker and Shaffer (1961) have given the average intraocular tension in normal healthy eyes with Schiotz Tonometer as 16.1 mmHg (± 2.5) and with Goldman applanation tonometer as 15.4 mmHg (± 2.5). According to this study intraocular pressure of over 21 mmHg occurs in less than 2.5% and a pressure above 25 mmHg occurs in less than 0.15%. We have not been able to find any reference from Indian authors in his connection.
In the present survey conducted by Glaucoma Clinic at the Haji Bachooalli Eye Hospital, Parel, Bombay, 400 normal healthy eyes were examined to calculate the average normal intraocular tension and the pattern of distribution of the various ranges of the tension in the normal subjects. The influences of age, sex and refractive errors are further discussed.
| Procedure|| |
1. Selection of cases - Cases were selected from the refraction department. To qualify for inclusion in the study, the subjects must have at least 6/9 vision with or without glasses, with no fundus changes and no evidence on examination or interrogation of present or past major ophthalmic disorder. Eyes which showed evidence of healed trachoma were included whereas red eyes even due to minor causes were dropped.
All cases were examined in the supine position with Schiotz tonometer (1955 calibration table). A single weight of 5.5 g. was used and all recordings were carried out personally by one of us with one instrument only. In all cases readings were taken more than once. Any reading which was not consistent with other series of readings on the same eye was discarded as a wrong reading. Patients who were non-coperative and could not keep their eyes open without pressure were dropped from the series. All cases where the tension was recorded above 21 mmHg were further investigated for the presence of Glaucoma and only those were included when the same was not established in its apparent or latent form.
Fields examination and provocative tests were carried out in such doubtful cases to exclude the possibility of glaucoma.
A total of 400 eyes were examined and the findings are tabled as follows:
From our findings it appears that there is maximum concentration in the range group between 15 - 19 mmHg with about equal spill over on either side of this group.
Another striking feature which impressed us was the similarity of the tension in the two eyes. Indeed the average difference between the two eyes was found to be as low as 0.12 mmHg. We feel this is a significant factor to be kept under consideration in the diagnosis of Glaucoma. If any one eye shows significantly higher tension than its fellow eye, it must be subjected to glaucoma investigations.
[Table - 3] shows the range variations according to the various age groups and compared with the average range variations of [Table - 2].
From this it appears that there is no significant influence of age on the normal tension.
[Table - 4] shows the range variation in relation to sex.
Again there does not seem to be any impressive difference between the readings for males and females. Although there do appear more cases of lower range tension in the females and more of the higher range tension in the males, there are only 12% eyes in the females with tension above 19 mmHg as against 18% in the average normal group and 227 in the male series. [Table - 5] deals with the range variation in relation to the refractive error.
Again there does not appear to be any significant influence of refractive error on the normal tension.
| References|| |
Davson H. (1962) - The Eye, New York: Academic Press Inc.
Duke-Elder S. (1962) - System of Ophthalmology, Vol. VII London, Henry Kimpton
Smih Redmond J. H. (1965) Clinical Glaucoma, London, Cassel & Co.
Sugar H. S. (1951) - The Glaucomas, St. Louis, C. V. Mosby Co.
Adler F. H. (1965) - Physiology of the Eye, St. Louis, C. V. Mosby
Becher B & Shaffer R. N. - Diagnosis and Therapy of the Glaucomas St. Louis, C. V. Mosby
Duke; Elder (1957) Glaucoma Symposium, Oxford, Blacwell Scientific Publication.
[Table - 1], [Table - 2], [Table - 3], [Table - 4], [Table - 5]