Tonometry with#the - bjo.bmj.com filetonometer with a convex plunger 117 table i deflection of...

1 IHE BRITIrSH J OURNAL OF OPHTHALAIOLOGY

Naumoff,--Ueber einige path. anat. Veranderungen im Augengrunde beineugebor. Kindern. Arch. f. O>ht1lal., Bd. XXXVI.

Parsons.-The pathology of the eye. Vol. III, pt. i, 1906Schleich.-Mittheilungen aus der ophthal. Klinik in Tubingen. 1884.Silcock, A. Quarry.-Trans. Ophthal. Soc. U.K., Vol. XX, 1900.Strahl. -Zur Entwickel. des menschl. Auges. Anat. Anzeig. Bd. XIV, 1898.Stumpf and Sicherer.-Beitrage zur Geburtshilfe u. Gynaek. 13d. XIII,

S. 408, 1909.Thomson,W. E. and Buchanan, L.-A clinical and pathological account of

some of the injuries to the eye of the child during labour. Traui.s.Ofhthal. Soc. U.K., Vol. XXIII, p. 296, 1903.

von Hippel, E.-Pathologico-anatomical changes in the eyes of the new-born.Arch f. Of lthal., Bd XLV.

Vossius.-Beitrage zur Anat. des. Nervus opticus. Arch. f. Ofhthal.,Bd. XXIX, H. iv, 1883.

Williamson-Noble.-Proc. Oiththal. Sec. Roy. Soc. Med., Vol. XIX, No. 8,p. 14, June, 1926.

Zimmermann. --Klinz. Monzatsbl. f. A ugeniheilk., lid. XXXV, 1897.

TONOMETRY: A TONOMETER WITHCONVEX PLUNGER

BY

Hj. SCHL6TZOSLO

IN my article "Tonometry" in the Brit. Ji. of. Ophthal., 11920,were described my attempts to introduce a change in the construc-tion of the tonometer, together with#the significance of the variousparts. Under the heading "The Plunger," I recorded certainmeasurements obtained respectively with plingers having theordinary concave end-surface, a plane surface, and a convexsuirface. Tlhey showed a surprising difference in the deflectionsof the pointer, especially as between the concave and the convexsturftaces.As stated in my previous article, my laboratory experiments were

made on a small metal drum closed above by a thin rubber menm-brane as a substitute for the eye, the drum being connected witha water-manometer, and the connection being opened or closedby means of a tap immediately below the drum. The resultsobtained respectively with the concave and convex plungers, andwith op-en and closed connection, were shown in a table herereproduced (Table I). WVith a low manometric pressure (30 cm.H20) and open connection the deflection differed by about 8 mm.With increasing pressure the difference diminished, but even at80-90 cm. H20, when the concave plunger put the pointer at 0),the convex put it at 3-4 mm., and even with a pressure of 120 cm.'it still gave a deflection of 1.6 mm.This great difference was surprising but the explanation is verx

simple: in each case the plunger sinks into the membrane and

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TONOMETER WITH A CONVEX PLUNGER 117

TABLE I

DEFLECTION OF POINTER (DRUM)

PRESSURE

CONCAVE PLUNGER CONVEX PLUNGER

H20. OPEN CLOSED OPEN CLOSED

cm. mm. mm. mm. mm.5 ... ... _11.0 - 19.310 ... ... 1 7.5 16.020 ... ... 14.0 4.3 - 11.530 ... ... 6.0 3.0 15.2 8.540 ... ... 3.5 1.7 10.7 6.350 ... ... 2.3 1.0 7.5 5.060 ... ... 1.5 0.4 6.0 4.270 ... ... 1.0 0.0 4.9 3.580 ... ... 0.3 - 4.0 3.090 ... ... 0.0 _ 3.2 2.3100 ... ... - - 2.6 2.0110 ... ... 2.0 + 1.6120 ... ... -1.6 1.0

depresses it until thle depressed area is supported from )below l)\a pressure that balances the weight of the plunger and its con-trolling parts; in eaclh case the "supporting area" is tile same butto obtain it the convex plunger m1iust sink more deeply tlhan theconcave (Fig. 1).*

FIG. 1.

Hence it follows that with a convex plunger and a relativelyssmall weioht one can deal wVitli a large range of pressures and Itlhoughlt in my earlier work (1920), that one ouglit perhaps tosubstitute a convex plunger for thie concave, in order to avoid thetroublesome addition and remioval of weiglhts and tile need for thecorresponding four curves. B3ut on the other lhand, I feared tllatthle relatively small intervals between the deflections obtained withtihe convex plunger in the case of hligh pressure wotuld m-ake tilemleasurements less trustwortiyv, and would therefore raise objec-tion to the proposed clhange.

BLut I have not been able to abandon the idea of tlhe convex* Priestley Smith. " The Blood Pressure in the Eye." Brit. JI. of Ophthal.'

p. 453, October, 1923.



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118 THE BRIT-ISH JOURNAL OF OPHT1 HALAIOLOGY

plunger, for further experiments show-ed that just in the regionwhich concerns us most, the deflections are not smaller but con-siderably larger than with the concave plunger. I have, therefore,worked further with the convex plunger in order to find the weightmost stlitable for clinical use and have arrived at 5.2 grin. (for theplunger and its belongings) as the best. This weight gives asufficiently large range, namely, from 5.6 mm. Hg (deflectionabout 22 mm.) up to 90 mm. Hg (deflection 0). In the exceptionalcases of higher pressure one can add a weight of 2 grm. and there-with measure up to 120 mm. Hg. The plunger has a diameterof 3 mm. and its tip is hemispherical.

I have named the tonometer with convex plunger the "Schi6tzx-Tonometer." The new model differs from the old not only inthe form of the plunger, but in having in place of the 5.5 grm.weight only a wire-support for the upper end of the pltinger. The2 grm. weight can be placed easily on the end of the plunger.With this tonometer I have carried out measurements on 40

eyes in situ after death, namely, on 10 by means of three differentweights and on 30 with the above-mentioned 5.2 grm. weight.They were made with a canula in the anterior chamber as describedin the Brit. Jl. of Ophthal., May, 1920; the lumen of the canulawas 1 mm.The average readings of the 30 eyes are shown in Table 2. I

lhave corrected them slightly on the basis of the results obtainedwith the three different weights, but the difference between the

TABLE II

Deflection of Pointer. (In situ after death.)

PressurellOpen Closed

H20 Observed Corrected Maximum Minimum Observed Corrected Maximum Minimumn________________I__________________________

cm. mm. mm. mm. mm. mm. mm. mm. mm.5 - - - - 19.40 21.0 21.7 16.510 - - - 17.10 18.4 20.1 12.720 - - - 13.50 14.0 17.6 10.230 17.90 17.9 20.9 14.3 10.76 11.0 13.0 8.940 13.90 13.8 16.0 11.8 8.83 8.8 11.0 7.050 10.60 10.5 12.6 8.8 7.10 7.1 9.0 5.160 7.70 8.0 9.6 6.3 6.00± 5.6 7.2 4.070 5.80 5.9 + 7.1 4.6 4.33 4.4 5.6 2.780 4.30 4.2 5.3 3.1 3.17 3.3 4.7 1.690 3.15 3.0 4.0 2.0 2.28 2.3 3.7 1.4100 2.00 2.0 3.0 1.5 1.39 1.6 3.0 0.6110 1.30 1.2 2.0 0.1 0.76 0.8 2.0 0.0120 0.73 0.3 1.5 0.0 0.00 0.1 0.9 0.0130 0.40 0.0 1.0 0.0 -- - 0.0 -

135 0.00 -- - - -



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TONOMAIETER WITH A CONVEX PLUNGEIR

observed and the corrected vcalues is small. The maxima, and,minimia also are sliglhtly corrected in accordance with the averagecurve.Diagram I shows the mercury values : the averacges by a con-

tinuous line; the maximtia aind minimna by dotted lines. The

Sr 'f q' ff rDIAGRAM 1.--Deflection of Pointer.

intervals between the latter arelhere somewxhat greater than theyw7ere with the concave piuinger (Brit. 11. of Ophtthal., AMay, 1920),for with low presssure we have a difference of 12 mm. H,, and withihiilh pressure a-s mtich als 2() mm. H-, while with the concaveplung-er wvith 5 .5 grin. weight we had 63-8 mm. Hg, and with 10 grini.weighit about 13 mm. H(g. Above.niSmm. Hg (with 10 grrm. weiglht)the old and new curves nearly coincide: at lower levels the curveg,iven by the convex plunger is the higher of the two.

In living eyes the readings given by the x-tonometer and the

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120 THE BRITISH JOURNAL OF OPHTHALMOLOGY

old instrument respectively should in ev-ery case have the samemercury values and this is nearly, the case though a slight differenceis noticeable througlhout. For this reason many comparativemieaLsuremiients were nmade. Thuts in D)iagran 2 the dotted lineshows th-e average valtues of thle somewhat variable deflections

X-TONOMETER (EYES IN SITU AFTER DEATH)

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DIAGRAm 2.-Deflection of Pointer.

found witlh tlle convex plunger, whlile thle continuous line showsthose that were given by the same living eye witlh the concaveplunger; the continuous line is the same as that in Diagram 1.As will be seen the curves coincide above, while below 70 mm. 1-Igthe dotted line is the lower of thle two, ancl lower still they crossand again separate sligyhtlyr.This dotted line, lhowever, must be taken as the normal curve

for the x-tonometer. Its values together with those given when

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TONOMIETER WITH A CONVEX PLUNGER 121

the 2 gr,i-n. weighlt is added as sho'wn in Trable III and the corre-sponding curves in Diagram 3.Here it must be stated that wArhen comparative measurements witlh

the two instruments are made on the same eye the readings areequally constant in each, but when they are made on a numlberof different eyes it is noticeable that in cases whlere the concave

TABLE III

DEFLECTION OF POINTER DEFLECTION OF POINTERI'RESSURE PRESSUREE

HG 2grm-WEIGHT HG 2grm. WEIGHTADDED ADDED

mm. mm. mm. mm. mm. mm.8 ... 20.0 _ 70 1.8 4.40

10 ... 17.6 - 80 0.8 3.2520 ... 11.7 - 90 0.0 2.2530 ... 8.5 _ 100 - 1.4040 ... 6.0 - 110 - 0.5050 ... 4.2 - 118 - 0.0060 ... 2.9 5.7 _ - -

plunger gives uniform readings, the convex often slhows slightvariations which could halrdly be attributed to error. Thlus in30 eyes where the concave plunger gave a reading of 5 mmn1.(22 mm. Hg), the convex, in ten of themii, gave 11 mm. (22' mm.Hg), in six of thenm it gave 11.5 mml., in four 10.5 mm., in six12 mm., and in four it gave 10 mm.

I think that these small discrepancies are perlhaps due to smllllldifferences in the tlhickness and elasticity of the cornea, so smallthlat thie flatter surface of the concave plung,er is not influenced bythlem, while the convex plunger which sinks deeper and is moreclosely surr-ounded by the cornea is sensitive to them. The greatdifference between the maIXimum and minimum values in the lattercase favours this idea.Now the question is whliclh plunger is to l)e preferred? I think

that for the present at aLny rate it will be well to retain the concave.This tononmeter has now been tried for many years and lhas slhownitself-whent correctly stantdardized-to be a practical instrumentfor clinical use. The earlier disadvantage of lhaving to screw theadditional weights on and off is done away with, for the originalxeight of 5.5 grmn. can now be added to by simply laying on it the7.5 grm., 10 grm., or 15 grni. weighlt. To clean the plunger andlcylinder the one weight needs to be remnoved, otherwise it remainsalways in place.

I must add, however, that the x-tonometer also is a goodinstrument, it g-ives a constant deflection and unquestionably it



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122 THE BRITISH JOUTRNAL OF OPHTHALMOLOGY

is safer for the corneal epitl-helium, especially in eyes with hiighpressure for which withi the concave plunger one must use aproportionately high weiglht.

GRAPHS FOR THE SCHIOTZ X-TONOMETER. 1926.

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DIAGRAM 3.-Deflection of Pointer.

The standardizing of the x-tonometer is not more difficult thanthat of the other instrument; in both cases it involves much time,for before the apparaitus is sent out it should be tested severaltimes at intervals of some days. The x-tonometer, like the other,can be obtained through Diplomingenieur Arnt Tandberg,Langesgate 7, Oslo.

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