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 was withdrawn for at least 24 hours before beginning http://bjo.bmj.com/ This effect is probably related to an increase in the the study.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= <ooI); this increased up to 30 minutes, s : but it did not increase after 6o minutes. The anterior 90 #;5 ..S: - chamber volume was found to be well correlated with + :: *- the anterior chamber depth as shown in Fig. 3. * *2.t . " 70- * * tA sZ tE. CHANGES IN LENS RADIUS OF CURVATURE (Table III) S .* * 50 :.w* In all the lenses measured, the radius of curvature of 5. *- the anterior surface became shorter with pilocarpine. The change in radius was highly significantly correlated 30 (r=o 84) with the degree of myopic change in refraction. * * w *B * w * W * W * * - The change in radius was also highly significantly 0 10 I5 2-0 2-5 3.0 3.5 4'0 correlated (r=o-84) with the change in anterior chamber Anterior chamber depth in mm depth and inversely r= o 84 with the age of the subject. FIG. 3 Correlation between volume and depth of anterior chamber Table II Changes in anterior chamber dimensions with pilocarpine Discussion Mean values for 125 eyes http://bjo.bmj.com/ This decrease in the depth of the anterior chamber Without After pilocarpine as a result of pilocarpine confirms earlier reports pilo- (Heim, I941; Rosengren, I950; T6rnqvist, 1956; carpine 15 min 30 min 6o min Bleeker, I960; Abramson and others, 1972). The change in visual acuity for distance appears AC depth (mm) 2z82 2-38 2-27 2.25 to be accounted for by a myopic shift since the Area (mm") 21vO i6.5 i5.8 I5.7 visual acuity could be corrected to pretreatment on October 4, 2021 by guest. Protected copyright. Volume (1±1) 155 117 112 III levels, in all patients in whom it was reduced, by the addition of minus lenses. The small reduction in radius of curvature of Table III Radius of curvature of the anterior the cornea after pilocarpine had been instilled is lens surface before and after pilocarpine likely to be related directly to the fall in intraocular pressure. The reduction in radius alone would Age Before After (years) pilocarpine pilocarpine produce a myopic shift, but it is likely to be out- weighed by an accompanying reduction in axial (mm) (mm) length of the globe. It has previously been shown I 73 I2-5 9'3 (Poinoosawmy and Roth, 1974) that raised intra- 2 39 14'8 9'3 ocular pressure is associated with an increase in 3 68 13'5 Io'9 the radius of curvature of the cornea and with a 4 74 112 Io'6 myopic shift which appears to be due to increased 5 45 I2 7 9,7 axial length of the globe. Thus the small changes 6 73 IO-I 8-I in external dimensions of the eye resulting from 7 77 I2.8 9'4 reduced intraocular pressure 8 75 i i8 would probably IIO0 result in a net hypermetropic shift.