THE INHERITANCE OF GLAUCOMA 95

REFERENCES

1. Duke-Elder, W. S. : Textbook of Ophthalmology. St. Louis, Mosby, 1941, v. 3, pp. 331-332. 2. François, J. : Heredity in Ophthalmology. St. Louis, Mosby, 1961, p. 219. 3. Reed, H., and Bendor-Samuel, J. E. L. : The early detection of glaucoma. Canad. M. A. J., 78 :6,

19S8. 4. Miller, S. J. H., and Paterson, G. D. : Studies on glaucoma relatives. Brit. J. Ophth., 46:513, 1962. 5. François, J. : Heredity in Ophthalmology. St. Louis, Mosby, 1961, pp. 231-232. 6. Wolff, E. : The Anatomy of the Eye and Orbit. London, Lewis, 1954, ed. 4, p. 33. 7. Moses, R. A., and Becker, B. : Clinical tonography : The scierai rigidity correction factor. Am. J.

Ophth., 45:196, 1958. 8. Garner, L. L., et al. : Effect of two-percent levorotary epinephrine on the intraocular pressure of the

glaucomatous eye. Arch. Ophth., 62 :230, 1959. 9. Sugar, H. S. : The Glaucomas. New York, Hoeber, 1957, ed. 2, pp. 409-415. 10. Harris, D. : Sympathetic ophthalmia following iridencleises. Am. J. Ophth., 51:829, 1961. 11. Moffatt, P.: Difficulties in the treatment of glaucoma. Tr. Ophth. Soc. U. Kingdom, 77:615, 1957.

C L I N I C A L E V A L U A T I O N O F A P P L A N A T I O N A N D S C H I 0 T Z T O N O M E T R Y *

F R A N K L. SEEGER, M.D., A L I C E R. D E U T S C H , M.D., M E L V I N W . DEWEESE, M.D.,

P H I L I P M. L E W I S , M.D., H E N R Y PACKER, M.D., AND M A R K KASHGARIAN, M.D.

Memphis, Tennessee

INTRODUCTION

Indentation tonometry with a Schio'tz type of tonometer has enjoyed wide popularity among ophthalmologists, and justly so. Prob-ably the principle source of error inherent in this type of tonometry lies in the varia-tion of ocular rigidity among different eyes. Schmidt has stated that Schijzitz tonometry causes 6.0-30 μΐ. of volumetric displacement covering a measuring range between 10 and 30 mm Hg, the exact amount depending on the reading and weight used.9 Therefore the intraocular pressure is artificially raised 15-25 mm H g when the Schijftz tonometer is applied to the eye2 and, from the amount of corneal indentation produced, the true intra-ocular pressure, Po, is computed according to Friedenwald's 1955 calibration table which assumes an average coefficient of ocular rigidity, E, of 0.0215.

Schmidt determined the ocular rigidity of 384 eyes (young patients and old, glauco-matous eyes, myopes, recently operated eyes) and found the average coefficient of ocular

* From the Departments of Ophthalmology and Preventive Medicine, University of Tennessee Col-lege of Medicine.

rigidity to be 0.01908.9 H e showed that, ac-cording to this series, with an intraocular pressure determination of 25 mm H g with a Schio'tz tonometer (7.5-gm weight) using Friedenwald's 1955 calibration tables, the true intraocular pressure would be between 23.5 and 26.5 mm H g only 31 .5% of the t ime; moreover, 2 6 % would have an error over ± 4.5 mm H g ; 14% over ± 6.0 mm H g ; 8% over ± 7.5 mm H g ; 4 % over ± 9.0 mm H g ; 1% over ± 12.5 mm Hg.10

In general, ocular rigidity is highest in high hypermétropes and lowest in the higher ranges of myopia.3 Furthermore, ocular rig-idity may change in individual eyes. Drance states that glaucomatous eyes with a high initial E often show a decreased E after treatment is instituted; conversely glauco-matous eyes with a low initial E often show an increase in ocular rigidity after treat-ment.3 H e believes that miotics decrease E in 2 5 % of glaucomatous patients; therefore, lower Schli tz pressure readings may not all be due to a reduction of Po. Ocular rigidity also tends to decrease during the water-provocative test.3

Since the coefficient of ocular rigidity is

96 SEEGER, DEUTSCH, DEWEESE, LEWIS, PACKER AND KASHGARIAN

the factor that relates changes in intraocu-lar volume to alterations in pressure, Samp-son and Girard have computed volume cor-rected scierai rigidity coefficient, Kv, by sub-stituting the percentage volume change for the absolute volume change in Friedenwald's formula. In a series of cats' eyes they found much less variation in Kv between eyes of different initial volumes than in computing E according to Friedenwald's formula. Therefore they concluded that the variation in E so often present among human eyes is due more to variations in intraocular vol-ume and less to actual differences in the pliancy or rigidity of the scierai coat than has been realized.8 This would agree with the previous observation that high myopes tend to have a lower E, and vice versa.

The Goldmann applanation tonometer measures the force necessary to flatten a small corneal area of constant size (3.06-mm diameter circle).5·10 The main advan-tage of this instrument lies in the small amount of volume displacement it produces, about 0.44 μΐ.3 The intraocular pressure is therefore raised only 2.5% (about 0.5 mm Hg) ; therefore, variations in ocular rigidity and corneal curvature affect the measured pressure so slightly as to be virtually ig-nored.2'5'6'10 Applanation reading error is said to be less than Schlitz because several readings can be taken and averaged at one sitting without significant massage effect which would lower the intraocular pres-sure.10

Besides these differences between Schio'tz and applanation tonometry, it must be re-membered that Schio'tz readings are taken in a reclining or semireclining position, while applanation tonometry is done with the patient seated at the slitlamp. Galin, et al., determined the applanation pressure of 20 patients in the erect and reclining posi-tion and found that the average increase in the latter position was 3.05 mm Hg, O.D., and 2.65 mm Hg, O.S., and that the variation was from minus 2.0 to plus 6.0 mm Hg.4 In a simi-lar study1 the applanation pressure increase

averaged 2.63 mm Hg. In this series,1 the authors calculated the coefficient of ocular rigidity on the basis of Schio'tz tonometry and erect applanation readings and found it to be 0.0238 ; E calculated on the basis of Schio'tz and reclining applanation tonometry was 0.0175.

In spite of the advantages of the Gold-mann applanation tonometer, it has not re-ceived the widespread use approaching that of the Schio'tz instrument presumably be-cause of the increased cost and the time in-volved in its use coupled with the fact that the determination of intraocular pressure is only one of the factors involved in the diag-nosis of glaucoma. Consequently, it seems advisable to investigate, with a large group of patients receiving a thorough glaucoma evaluation, just how important is the differ-ence in accuracy between the Goldmann and Schio'tz tonometers in the diagnosis of glau-coma.

METHOD

A glaucoma detection program based in the City of Memphis Hospitals provided the clinical material on which this study is based. Between July 1, 1961, and June 30, 1963, 9,243 persons over 40 years of age were screened with Schio'tz tonometry (7.5-gm weight) performed by registered nurses spe-cially trained in the practice of tonometry by the staff of the ophthalmology clinic. From this population, which consisted of (a) presumably well health-card applicants, (b) general medicine clinic patients, and (c) new eye clinic patients, certain proportions were selected for complete glaucoma evalua-tion as follows:

OCULAR TENSION (mm Hg) EXAMINKD

23.8 and above All persons 21.9 1 in 5 20.1 1 in 10

Below 20.1 1 in 100

The glaucoma evaluation consisted of re-peated retesting with a SchipStz tonometer and different weights, applanation tonom-etry, tonography with and without water

APPLANATION AND SCHI0TZ TONOMETRY 97

provocation, central and peripheral fields of vision, visual acuity, funduscopy, gonioscopy, diurnal variation tests and mydriatic tests when indicated. The patients were then clas-sified as positive, borderline or negative for primary glaucoma (secondary glaucoma was excluded from the data), and the borderline patients were retested and evaluated at three-to six-month intervals until many of these could be reclassified as positive or negative. The criteria for positive and borderline diagnoses and the results of the survey are the subject of another paper.7

RESULTS

Of the 712 persons extensively examined and tested for glaucoma, it was later dis-covered that 61 had unrecorded applanation pressures. The data from 17 others are omitted because of pressure readings noted as unsatisfactory or because of detected "errors" in procedure, recording of data, etc., which would erroneously negate any possible correlation between Schijzitz and ap-planation pressures. Therefore, the data

from 634 patients are available for analysis. Table 1 shows the number of patients

within each pressure range (using the eye with the highest tension), both for Schip'tz and applanation readings, and the percentage of each corresponding group that was diag-nosed as having glaucoma. The Schlitz ten-sions listed are the first ones taken on each patient, and the applanation pressure is the only one taken. It can be seen from the table that for almost every given pressure range, the applanation group shows a higher percentage of glaucomatous patients. How-ever, this is to be expected as we have learned that, on the average, the applanation readings are lower than Schip'tz ; therefore, a given patient is likely to be in a higher pressure range on the Schi^tz side of the table. This is reflected by the number of pa-tients in each pressure range being greater on the Schip'tz side for the higher pressures, and greater on the applanation side for the lower pressures.

Figure 1 graphically pictures the results tabulated in the table. The fact that the ap-

TABLE 1

APPLANATION AND INITIAL SCHI0TZ INTRAOCULAR PRESSURE READINGS

%. Positive

100 —

100 100 86 83 69 48 19 24

5 7 2 0 0 0 0 0

— 0 0

INCIDENCE

Schi0tz (7.5 gm w

Number of Patients

6 0 3 1 7 6

29 21

112 79

134 106 61 22 19 5 8 5 0 9 1

OF

•t)

OF 634 PATIENTS PRIMARY GLAUCOMA IN EACH PRESSURE RANGE

Intraocular Pressure (mm Hg)

over 45.8 45.8 42.1 38.9 35.8 33.0 30.4 28.0 25.8 23.8 21.9 20.1 18.5 17.0 15.6 14.3 13.1 12.0 10.9 10.0 9.1

Intraocular Pressure (mm Hg)

48 and over 44-47 41-43 38-40 35-37 32-34 30-31 27-29 25-26 23-24 21-22

20 18-19

17 15-16

14 13 12 11 10 9

Applanation

Number of Patients

1 0 1 1 1 7

IS 19 27 47 80 85

117 38

108 40 11 16 6

12 2

SHOWING THE

%. Positive

100 —

100 100 100 86 93 89 37 49 19 14 2 0 2 0 0 0 0 0 0

98 SEEGER, DEUTSCH, DEWEESE, LEWIS, PACKER AND KASHGARIAN

mm, Hg.

5 ~ i i » i i i 100 80 60 40 20 0

% Pos i t i ve

Fig. 1 (Seeger, et al.). Applanation and Schlitz pressure readings plotted against frequency of glau-

planation curve runs below the Schip'tz is not our main concern. What we are interested in is the fact that the applanation curve, in the intermediate ranges of pressure where the presence or absence of glaucoma is more difficult to determine, seems to be a bit flatter than the Schip'tz curve. If this is true, it would mean that a high "borderline" ten-sion (without attempting to define the boun-daries of a "borderline range" that separate normal from elevated tensions) taken with an applanation tonometer is more likely to be from a glaucomatous patient than if the tension was taken with a Schip'tz tonome-ter ; conversely a low "borderline" applana-tion tension would be more likely to be from a nonglaucomatous patient that if taken with a Schi^tz tonometer. Of course the numerical values of an applanation "borderline range" would be lower than for a similar S c h ä t z group because applanation pressures tend to be slightly lower. To try to compensate gra-phically for the effect of erect and reclining positions on intraocular pressure, Figure 2 shows the same curves as given in Figure 1

but with the applanation curve arbitrarily raised 2.75 mm Hg. This shows the differ-ence in the slope of the lines even better be-cause one is seen to cross the other.

These data on percentages of glaucoma all refer to the initial diagnosis of the glau-coma detection program. Similar figures based on the number of positives after re-classification of several of the borderline patients showed almost the same relationship between the two curves, and so will not be presented.

It must be remembered that in this series it is the same group of patients that are an-alyzed according to initial Schip'tz and ap-planation tonometry. Therefore, the number of glaucoma cases found after extensive testing is the same for both types of tonom-etry. However, it does seem that applanation tonometry shows a slightly better correlation of intraocular pressure with the diagnosis of glaucoma than does Schip'tz tonometry. Thus, without benefit of a routine extensive glaucoma investigation, applanation tonome-ter readings would more accurately show whether a given patient does or does not

50 -

mm. H g .

I I % · · '

100 80 60 40 20 0 % Pos i t ive

FIG. 2 (Seeger, et al.). Applanation (raised 2.75 mm Hg) and Schi0tz pressure readings plotted against frequency of glaucoma.

APPLANATION AND SCHI0TZ TONOMETRY 99

have glaucoma. To put it another way, we might say that the applanation "borderline range" of pressure is narrower than the Schip'tz.

Before this line of reasoning is carried too far, we can readily see that the differ-ence in the shape and slope of the two curves in Figures 1 and 2 is not great. The greater scatter of the plotted applanation points about the curve in Figure 1 than of Schip'tz points is probably a reflection of less fa-miliarity and experience with the applana-tion instrument on the part of the resident staff of the eye clinic. Furthermore, the in-itial Schip'tz and applanation pressures were not determined at the same time but on dif-ferent days. If these factors had not been present, it is possible that the shape and slope of the two curves would have shown a greater difference, but it would be only conjecture to assume so.

While the results of this analysis do favor

Mr. President, Sir Stewart, guests, and members, as the oldest member and one who

* Presented at the 100th annual meeting of the American Ophthalmological Society, Hot Springs, Virginia, May, 1964.

applanation tonometry, we can only repeat that the intraocular pressure determination is merely one factor, although an important one, involved in the early diagnosis of glau-coma. In this perspective, it is difficult tc say just how much clinical significance should be attached to the differences in re-sults we have shown between these two methods of tonometry.

S U M M A R Y

1. Schip'tz and applanation intraocular pressure readings of 634 patients being evaluated for glaucoma are analyzed accord-ing to the subsequent diagnosis of glaucoma.

2. In the intermediate ranges of ocular tension where the diagnosis Of glaucoma is more difficult to prove or exclude, applana-tion tonometry correlated slightly better than Schip'tz with the subsequent diagnosis of glaucoma.

1060 Madison Avenue.

was present at both the 50th-year celebra-tion and the 75th anniversary, it is a great pleasure to participate in this centenary.

Ocular pemphigus is a rare disease. This report is based on my experience with 13

REFERENCES

1. Armaly, Mansour F., and Salamoun, Samir G. : Schi^tz and applanation tonometry. Arch. Ophth., 70:603-609, 1963.

2. Becker, B., and Shaffer, R. N. : Diagnosis and Therapy of the Glaucomas. St. Louis, Mosby, 1961. 3. Drance, S. M. : The coefficient of scierai rigidity in normal and glaucomatous eyes. Arch. Ophth.,

63:668-674, 1960. 4. Galin, M. A., Mclvor, J. W., and Magruder, G. B. : Influence of position on intraocular pressure.

Am. J. Ophth., 55 -.720-723, 1963. 5. Goldmann, H. : Applanation tonometry. In Transactions of the Second Conference on Glaucoma

(edited by F. W. Newell). New York, Macy, 1957. 6. Moses, R. A. : The Goldmann applanation tonometer. Am. J. Ophth., 46 :865-869, 19S8. 7. Packer, H., Deutsch, A. R., Deweese, M. W., Kashgarian, M., and Lewis, P. M. : Frequency of

glaucoma in three population groups. J. Am. Med. A., 188 :11S-119, 1964. 8. Sampson, W. G., and Girard, L. J. : The coefficient of scierai rigidity : Effect of variation of the

intraocular volume. Am. J. Ophth., 52 789-799 (Nov. Pt. II) 1961. 9. Schmidt, T. F. A. : The clinical application of the Goldmann applanation tonometer. Am. J. Ophth.,

49:967-978, 1960. 10. : On applanation tonometry. Trans. Am. Acad. Ophth. Otolaryng., 65:171-177, 1961.

O C U L A R P E M P H I G U S * A CLINICAL PRESENTATION OF KODACHROMES

A R T H U R J. BEDELL, M.D.

Albany, New York