Effect of Pilocarpineon Visual Acuity and On
Br J Ophthalmol: first published as 10.1136/bjo.60.10.676 on 1 October 1976. Downloaded from Brit. 7. Ophthal. (1976) 6o, 676
Effect of pilocarpine on visual acuity and on the dimensions of the cornea and anterior chamber
D. POINOOSAWMY, S. NAGASUBRAMANIAN, AND N. A. P. BROWN From the Department of Experimental Ophthalmology, Institute of Ophthalmology, London
There are many data on the effect of pilocarpine on the reduction in intraocular pressure resulting from the anterior chamber, particularly in respect to pilocarpine, but this has not previously been reduction in intraocular pressure and in anterior measured. The present study investigates the chamber depth and miosis, but the effect of pilo- effect of pilocarpine on the cornea with pachometry carpine on the anterior chamber volume and corneal and keratometry. curvature has not previously been studied. Pilo- carpine commonly causes reduced visual acuity Materials and methods which may be partly due to miosis, but in this study reduced visual acuity is shown to be mainly due to a SELECTION OF SUBJECTS of myopic change. The mechanism the myopic Altogether 105 patients of both sexes were selected. change has not previously been established and it They ranged in age from 35 to 70 years and included is now shown to be caused by changes in radius of normal subjects as well as patients with confirmed curvature of the lens, similar to changes occurring narrow-angle and chronic simple glaucomas. In all I8o in accommodation; changes in radius of curvature eyes were studied. of the cornea are relatively unimportant. Pilocarpine reduces the anterior chamber depth Methods (Heim, I94I; Rosengren, I950; T6rnqvist, 1956; Bleeker, 1960; Romano, I968; Wilkie, Drance, In those patients already receiving pilocarpine, the drug and Schulzer, I969; Poinoosawmy and Roth, I974). was withdrawn for at least 24 hours before beginning http://bjo.bmj.com/ This effect is probably related to an increase in the the study. The following parameters were studied sagittal width of the lens as demonstrated by before and after the administration of pilocarpine and, in some subjects, again after its withdrawal. ultrasound (Abramson, 1972; Abramson, Coleman, Visual acuity. Standard Snellen chart at 6 m (with Forbes, and Franzen, I972) and is not connected distance correction if required). with the reduction in intraocular pressure. In this Anterior chamber depth (Haag-Streit pachometer and study the reduction in anterior chamber depth is slit-image photography).
correlated with the reduction in anterior chamber Anterior chamber cross-section area (slit-image photo- on October 4, 2021 by guest. Protected copyright. volume and in the radius of curvature of the lens; graphy, from which anterior chamber volume was these have not hitherto been reported. calculated). Miosis may result in better visual acuity in some Comeal thickness (Haag-Streit pachometer). patients who are initially ametropic, but reduced Applanation tension (Goldmann). is Pupil diameter (pupillometer). visual acuity the more usual effect of pilocarpine. Lens anterior radius (slit-image photography). Visual acuity has been shown to improve if the The photographic method described by Jones and pupil diameter is reduced to 2-5 mm (Hallden, Maurice (I963) for measuring the volume of the anterior I973a and b) and to deteriorate with further chamber by means of attachments to the Haag-Streit reduction below this figure; this deterioration is goo slit-lamp was later modified (Brown, 1973a) to believed to be due to diffraction. The current study produce an improved image of the anterior chamber; shows that changes in visual acuity result from measurements were then made from the photographs factors unrelated to miosis. using a Perspex grid (Figs i and 2). The modified An increased radius of curvature of the cornea technique was used in the present study for measuring has been shown to occur with a rise in intraocular the depth and for calculating the volume of the anterior chamber. pressure (Poinoosawmy and Roth, 1974). Reduction The radius of curvature of the anterior surface of the in corneal radius is therefore to be anticipated with lens was measured in only i0 eyes in which the lens was well recorded in the photographs when Address for reprints: D. Poinoosawmy, Department of Experimental sufficiently Ophthalmology, Institute of Ophthalmology, Judd Street, London the pupil was miosed. The radii were measured from WCiH 9QS the projected images using the mirror technique as Br J Ophthalmol: first published as 10.1136/bjo.60.10.676 on 1 October 1976. Downloaded from
Effect of pilocarpine on visual acuity 677
(I) http://bjo.bmj.com/
(2) FIGS I and 2 Anterior segment photographs taken before (Fig. i) and after (Fig. 2) pilocarpine. Note distance between posterior surface of cornea and anterior surface of lens (3-1 mm before and 2-7 mm after administration) on October 4, 2021 by guest. Protected copyright. described by Fisher (I97i) and modified by Brown Table I Changes in cornea, intraocular pressure, (I973a) to allow for corneal refraction. and anterior chamber depth with pilocarpine Results Mean values from 55 eyes with glaucoma CHANGES IN CORNEA, INTRAOCULAR PRESSURE, AND ANTERIOR CHAMBER DEPTH WITH PILOCARPINE Without With (TABLE I) pilo- pilo- There was no change in comeal thickness, but there was carpine carpine Difference a significant reduction in the radii of curvature of both the horizontal and vertical meridia of the comeae with Corneal thickness (mm) 0-56 o-56 o pilocarpine, which correlated well with the reduction in Horizontal meridia intraocular pressure (r=o-64). There was also a signifi- (mm) 7-86 7-78 -o.o8* cant shallowing of the anterior chamber. Vertical meridia (mm) 7-90 7-8 I -o009* Intraocular pressure (mmHg) 3o07 I9-6 -II*I CHANGES IN VISUAL ACUITY WITH PILOCARPINE AC depth (mm) 2.72 2v6i -o-II* The visual acuity with pilocarpine in 102 glaucomatous eyes deteriorated in 78 eyes, improved in six, and was *Significant P = > o o5 Br J Ophthalmol: first published as 10.1136/bjo.60.10.676 on 1 October 1976. Downloaded from 678 British 3ournal of Ophthalmology
unchanged in the remainder. In those eyes in which the visual acuity deteriorated it fell from one to five lines 210' on the Snellen chart. In all these eyes the visual acuity * . ;* could be corrected to the previous value with the 190. * * * * addition of minus spheres to the distance refraction. :.T_ @ - s * - . s The correction needed varied from ** -o-25D to -I175D . s. with a mean value of o-95D. Miosis occurred in all 170- * ^ * eyes * . * but was evidently not the cause of the reduced visual . 4.. * * @ b- *: acuity since this could be corrected with minus lenses. 150' * * -t * **,, .t > * * t*:0 CHANGES IN ANTERIOR CHAMBER DIMENSIONS * * * - 130- .s. s WITH PILOCARPINE (Table II) : *@2. 2 . ._c There was a highly significant reduction in anterior * dd: *1 * .. *- chamber depth, area, and calculated volume within 15 ... * . :X: * minutes (P=
Effect ofpilocarpine on visual acuity 679
changes in the eye and it is likely that changes in obtained a value of 175+30 .Ll for the volume of the lens are responsible. A forward movement of the anterior chamber in normal subjects. The mean the anterior pole of the lens is demonstrated in all volume in the pretreated group in our study, which subjects in whom there is a myopic shift and io of included both normal and glaucomatous eyes, was these subjects in whom the radius of curvature of approximately I54-62+7'022I 0.l, and the slight the anterior lens surface could be measured showed difference could well be due to the inclusion of eyes a reduction in radius. The present study does not with shallow anterior chambers. measure the sagittal width of the position of the posterior pole of the lens. Summary It seems likely that the changes now observed The effect of pilocarpine on visual acuity and on in the lens ofthe eyes are the same as those occurring the dimensions of the cornea, anterior chamber, in accommodation in which the increase in sagittal and lens were studied in two groups of subjects. width of the lens is associated with a greater forward Significant changes in ocular tension, comeal movement of the anterior pole than backward curvature, anterior chamber depth, and lens movement of the posterior pole, so that there is a anterior radius were found in a group of 55 glau- forward movement of the lens centre (Coleman, comatous eyes as a result of pilocarpine treatment, 1970; Brown, 1973b). Similar changes have also but there was no change in corneal thickness. Out been demonstrated by ultrasound after pilocarpine of 102 glaucomatous eyes 78 became relatively administration (Abramson, I972). myopic, and this appears to be due to changes in Forward movement of the lens increases its the dimensions of the lens of the eye similar to effectiveness, but in accommodation it is mainly the those occurring in acconmnodation, as a result of change in lens radius of curvature which is res- the effect of the drug on the ciliary muscle. ponsible for producing near focus (Brown, I973b). The effect of pilocarpine on anterior chamber It is likely that the reduced radius of curvature of depth, area, and volume was studied in 125 eyes the lens is the main factor in producing myopia in using a photographic method, and a significant our subjects. reduction in the dimensions of the anterior chamber It appears that the myopia induced by pilocar- was observed as a result of the administration of pine is due to the action on the ciliary body causing pilocarpine. A significant correlation between depth it to contract and to produce the lens changes and volume was also noted and the implications of normally seen in accommodation. The myopic this are discussed.
changes were least in the older subjects as could be http://bjo.bmj.com/ in We thank Professor J. Gloster for allowing us to examine expected from the presbyopic reduction accom- his patients in the Glaucoma Clinic of the Institute of modation. Ophthalmology and Professor E. S. Perkins for useful Another interesting observation in the present discussions. study is the correlation between the depth and We acknowledge the help received from Mr Brian volume of the anterior chamber, which was found Augier for computing the results, and from Mrs Fiona to be highly significant. Jones and Maurice (I966) Dolamore for secretarial assistance. on October 4, 2021 by guest. Protected copyright. References ABRAMSON, D. H. (I972) Arch. Ophthal., 86, 643 , COLEMAN, D. J., FORBES, M., and FRANZEN, L. A. (1972) Ibid., 87, 615 BLEEKER, G. M. (I960) Ibid., 63, 821 BROWN, N. (1973a) Trans. ophthal. Soc. U.K., 93, 277 (1973b) Exp. Eye Res., I5, 44I COLEMAN, D. J. (1970) Amer. 3. Ophthal., 69, I063 FISHER, R. F. (I97I) Y. Physiol. (Lond.), 212, 147 HALLDEN, U. (I973a) Acta ophthal. (Kbh.), 51, 72 (1973b) Ibid., 5', 193 HEIM, M. (I94I) Ophthalmologica (Basel), 302, 193 JOMES, R. F., and MAURICE, D. M. (I963) Exp. Eye Res., 2, 233 , and (I966) Ibid., 5, 208 POINOOSAWMY, D., and ROTH, J. A. (i974) Brit. 7. Ophthal., 58, 523 ROSENGREN, B. (1950) Arch. Ophthal. (Chic.), 44, 523 ROMANO, J. (I968) Brit.J. Ophthal., 52, 36i TORNQVIST, R. (I956) Ibid., 40, 421 WILKIE, J., DRANCE, S. M., and SCHULZER, M. (I969) Amer. Y. Ophthal., 68, 78