A traumatic “peripheral iridotomy” protects against pigment dispersion and glaucoma
- Accepted 22 September 1998
Editor,—Pigment dispersion syndrome is an autosomal dominant condition which leads to pigmentary glaucoma in up to 50% of cases. Campbell1 was the first to propose that posterior bowing of the peripheral iris with chaffing against the lens zonule was responsible for the liberation of iris pigment which recent developments in high resolution ultrasound biomicroscopy appear to bear out. Current theories suggest that the cause of this posterior iris bowing is “reverse pupil block”,2 in which the iris acts as a flap valve against the anterior surface of the lens allowing aqueous to pass from posterior to anterior chamber but not vice versa.
Pigment dispersion syndrome is a bilateral, symmetric disorder and unilaterality or asymmetry should prompt further investigation as to the cause.3 An unusual case of unilateral pigmentary glaucoma is presented which is the first to report the possible long term protective benefits of relieving of this “reverse pupil block”.
CASE REPORT
A 39 year old man was referred after his optometrist had noted elevated intraocular pressure (IOP) in his right eye. He was myopic and had sustained a blunt injury to his left eye at the age of 8 after which the vision in that eye had been poor.
His corrected visual acuity was right eye 6/5 Snellen −1.25/−3.25×180 and left eye 6/24 Snellen −1.25/−1.50×175. IOPs at presentation were 35 mm Hg right and 20 mm Hg left. He had brown deeply pigmented irides bilaterally. His right eye showed inferocentral pigment deposition on the corneal endothelium (Krukenberg’s spindle) and mid-peripheral radial iris transillumination defects. The left cornea was clear and the only iris defects visible were a 2 clock hour iridodialysis and a partially denervated, ruptured iris sphincter muscle. Both anterior chambers appeared equally deep and gonioscopy revealed a wide open angle with a posteriorly inserted iris root in both eyes. In the left eye, on the borders of the dialysis only, there had probably been some iris recession. Heavy circumferential trabecular pigmentation was present in the right eye but no pigment was seen on the left. The right optic disc (Fig 1) was deeply cupped (vertical C/D 0.6/7) while the left the optic disc (Fig 2) was not cupped but was slightly pale and surrounded by chorioretinal scarring. Right eye threshold visual field examination was suggestive of a superior nasal step scotoma while the left showed an inferior altitudinal defect. A diagnosis of right pigmentary glaucoma was made and he was immediately started upon levobunolol twice daily in his right eye. Subsequently he has had a laser peripheral iridotomy performed.
Optic disc, cupped.
Optic disc, not cupped.
COMMENT
Much in the same way as conventional pupil block can be alleviated by an iridotomy (providing an alternative aqueous pathway and equalising anterior and posterior chamber IOP), it is suggested that “reverse pupil block” may also be alleviated in the same way. There is now evidence that laser peripheral iridotomy in pigment dispersion syndrome both restores a more planar iris configuration4 and may prevent the development of ocular hypertension.5 However, long term studies are awaited.
This report illustrates the effect of a traumatic iridotomy occurring in childhood in an individual who was destined subsequently to develop pigment dispersion syndrome and glaucoma. It would appear that the lack of pigment dispersion and optic disc cupping in the previously damaged eye provides evidence for the long term efficacy of laser peripheral iridotomy in this condition.
