A fixed dilated pupil is a recognized though rare postoperative complication of anterior segment surgery. It is classically described after penetrating keratoplasty (1) but also may occur after other anterior segment procedures including trabeculectomy (2) and cataract extraction (3). In these cases, the parasympathetic blockade is usually postreceptoral (because the pupil will not constrict with topically administered full-strength pilocarpine drops) and permanent. We describe an unusual case of a patient with a fixed dilated pupil after retinal detachment surgery in which parasympathetic function partially recovered after removal of the scleral encircling band.
A 23-year-old woman underwent surgery for a macula-off rhegmatogenous retinal detachment in her left eye. She had a moderate degree of myopia (−3D) but no other history of ocular disease. She enjoyed good general health and was taking no regular medications. The surgery, performed under general anesthetic, involved placement of a circumferential silicone explant (buckle) between the 11 o'clock and 4 o'clock meridians, a 360° encircling band (2.5 mm diameter) and transscleral cryopexy. The following day she noticed on removing the eye patch that her left pupil was dilated; ophthalmic examination confirmed successful reattachment of the retina. Postoperative recovery was unremarkable but the pupil remained dilated and nonreactive to light.
She returned 18 months, later having noticed problems focusing. Visual acuity was 20/20 in the right eye and 20/200 in the left eye. Anterior segment examination was unremarkable with normal intraocular pressures and no signs of ocular ischemia; funduscopy showed that the retina remained fully attached. Eye movements were full on the right but slightly restricted on the left both horizontally and vertically. The patient's eyelids were symmetric and normal. The left pupil was larger than the right (Fig. 1), and there was almost no observable light response (LR) or near response (NR) of the left pupil. On slit-lamp biomicroscopy, the pupil appeared round with no visible sector palsy. Pupillometry confirmed significant attenuation of the pupillary constrictor responses (LR and NR; Fig. 2, Table 1) in the left eye, although the mydriatic response to sudden noise (the “startle reflex”) was preserved. The right pupil and deep tendon reflexes were normal.
In view of her persistent symptoms, the patient underwent surgery to remove both segmental and encircling buckles, which were found lying 2 mm posterior to the insertions of the rectus muscles. During the surgical procedure and within minutes of cutting the encircling buckle, the left pupil became smaller. The following day the patient noticed that her left pupil was smaller than the right and when examined at her postoperative visit 2 weeks later the left pupil now reacted to light. Ten weeks after surgery, pupillometry showed that the left pupil was smaller, and the pupillary constrictions to a light stimulus and an accommodative effort were larger (Table 1; Figs. 1, 2). Pupillometry was repeated once more 4 months later and showed similar results. Topical 0.5% apraclonidine was used to test the integrity of the sympathetic innervation of the iris dilator muscle; this weak α1-agonist had no effect on the resting size of either pupil.
Although our patient did not have any previous pupil assessment, it is her recollection, supported by old photographs, that her pupils were normal and similar in size before retinal detachment surgery. Following this procedure, the left pupil became fixed and dilated. The lack of response to light can be partly attributed to a reduced afferent drive from the reattached retina. We did not record the pupil responses to uniocular light stimulation or look for a relative afferent pupil defect. However, this does not explain the increase in resting diameter of the left pupil or the absence of any pupil constriction with an accommodative effort. These changes suggest that surgery caused a marked efferent blockade of parasympathetic impulses to the iris sphincter muscle.
The findings in our patient's left pupil are not similar to Adie's tonic pupil, which include sector palsy, light-near dissociation, and slowed constriction associated with aberrant regeneration of postganglionic parasympathetic fibers after injury to the ciliary ganglion. The changes we noted are better described as atonic. It appears that this was a purely parasympathetic blockade. The normal lid position, preserved startle response, and absence of mydriatic effect from apraclonidine indicate that the sympathetic supply to the iris dilator muscle was unaffected. Also, there was no clinically apparent disturbance of corneal sensation.
Changes to the pupil and accommodation have been reported after various transscleral treatments for diabetic retinopathy or peripheral retinal degeneration—including cryotherapy (4), argon laser photocoagulation (5), and diode laser photocoagulation (6). Pupil changes have rarely been reported after retinal detachment surgery. Adler and Scheie (7) provided the first description of 2 cases of atonic pupils after “extensive (transscleral) electrocoagulation”; in patient 1, after several weeks the pupil became smaller and recovered a small degree of “tonic” responsiveness to light. Kronfeld (8) reported postoperative sector palsy in 5 eyes in which the affected meridian corresponded to the site of scleral buckling. There are a small number of additional cases published in which the pupil has become either tonic (9) or atonic (10,11) after placement of an encircling band or endolaser. In all cases, the pupil showed supersensitivity to dilute muscarinic agonists (methacholine or pilocarpine) confirming prereceptoral parasympathetic blockade and, in most cases, the pupil remained abnormal with no spontaneous recovery.
Our case is unique in documenting the effects of removing an encircling band in a patient who had developed an atonic pupil at the time of its placement. We would interpret the partial reversal of the parasympathetic paresis within minutes of removing the encircling band as evidence that the pupil changes were because of conduction block rather than loss of the short posterior ciliary nerves (SPCN). The lack of any pupil signs that might indicate aberrant regeneration (tonic constriction to light and near, sector palsy, and light-near dissociation) further supports our view that the SPCN were preserved but nonfunctioning between her first and second operations. It is not clear whether the mechanism of this conduction block was primarily ischemic or mechanical. There were no clinical signs suggestive of ocular ischemia. The SPCN travel in the suprachoroidal space as they pass forward towards the iris and are presumably susceptible to mechanical deformation from scleral indentation. It is interesting that in our patient there was no evidence of dysfunction of the sympathetic and trigeminal nerves, which also pass in the suprachoroidal space. In the case reported by Valldeperas et al (11), a 11-year-old boy developed permanent corneal anesthesia after placement of an encircling band; however, additional trigeminal or sympathetic paresis was not described in any of the other published cases of pupil changes after retinal detachment surgery and was not detectable in our case. We speculate that the SPCN may be more susceptible to mechanical deformation than the other nerves traveling in the same anatomical compartment.
After removal of the encircling band, the left pupil became smaller than the right and remained so 4 months later. This raises the question of whether the larger right pupil was functioning normally. The amplitude of the LR in this eye was below the lower limit of the normal range for our laboratory (12), and it is possible that the extensive prophylactic cryotherapy to this eye had damaged some of the SPCN giving rise to a larger than normal resting pupillary diameter in this eye. However, the light reflex response of the pupil in the left eye remained smaller than in the right eye even after removal the encircling band suggesting that the SPCN function was still better in the eye with the larger pupil. Different degrees of denervation supersensitivity might have accounted for some of this reversed anisocoria; in the context of SPCN dysfunction in Holmes–Adie syndrome, it is a common finding that affected pupils become progressively miotic over time despite persisting signs of parasympathetic paresis. Unfortunately, we were not able to test this hypothesis by pharmacological means using a dilute muscarinic agonist (e.g., 0.1% pilocarpine) because the corneal surfaces of both eyes in this myopic patient were compromised by years of contact lens wear rendering such testing invalid.
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