From Preston Eye Clinic, Melbourne, Australia.
The author has no financial or proprietary interest in the materials presented herein.
Address correspondence to Lance Liu, FRANZCO, Preston Eye Clinic, 268 Murray Road, Preston 3072, Australia. E-mail: email@example.com
Pigment dispersion syndrome is characterized by a loss of pigment from the mid-peripheral iris and is deposited throughout the anterior segment, including the trabecular meshwork. This can lead to a rise in intraocular pressure (IOP), which increases the risk of developing pigmentary glaucoma. The clinical triad consists of a vertical band of pigment on the central corneal endothelium (Krukenberg spindle), radial slit-like mid-peripheral iris transillumination defects, and dense pigmentation of the trabecular meshwork.1 These signs may not all be present at the time of diagnosis,2 especially in patients of African descent.3
Ultrasound biomicroscopy has shown a concave iris configuration can lead to iridozonular contact and pigment shedding,4,5 which may be explained by reverse pupil block. Anterior segment OCT (AS-OCT) provides a non-contact method of acquiring cross-sectional images of the anterior chamber.6 This case series consists of AS-OCT images of patients with pigment dispersion syndrome and no previous laser iridotomy who underwent cataract surgery.
A 63-year-old man presented with a gradual decline of his vision. There was an ocular history of myopia. The best-corrected visual acuity was 6/6 in the right eye and 6/36 in the left eye. The IOP was 14 mm Hg in both eyes and there were signs of pigment dispersion syndrome with cataracts. Fundus examination showed mild RPE changes near the left macula related to his myopia. Gonioscopy revealed a concave iris configuration in all four quadrants. AS-OCT showed the posterior bowing of the iris was associated with iridolenticular contact, which extended along a greater part of the anterior surface of the lens from dark to light lighting conditions (Figs. 1A and 1B).
Figure 1. Optical Coherence Tomography Images of the Anterior Chamber Angle (0° to 180°) of the Left Eye in Case 1 in (A) Dark and (B) Light Illumination Before Cataract Surgery. The Concave Iris Configuration Is Present Due to Iridolenticular Contact. (C) Following Cataract Surgery, the Concave Iris Becomes Flat with Loss of Contact Between the Iris and Intraocular Lens. The Same Changes Were also Seen in Dark Lighting Conditions. The Interscleral Spur Line (ISL) Joins the Tips of the Scleral Spur.
The benefits and risks of cataract surgery were discussed, including a guarded prognosis of the visual outcome. Then the patient underwent an uncomplicated phacoemulsification with an intraocular lens (IOL) inserted into the bag in the left eye. Postoperatively, the visual acuity improved to 6/9 in the left eye with a refraction and the IOP was 21 mm Hg. Gonioscopy revealed the iris to be flat and was confirmed by a repeat AS-OCT, which showed a planar configuration (Fig. 1C).
A 69-year-old man initially presented with watery eyes. There was an ocular history of hypermetropia. On examination, the best-corrected visual acuity was 6/6 in the right eye and 6/5 in the left eye. In both eyes, the IOP was 16 mm Hg and there were signs of pigment dispersion syndrome. Fundus examination was unremarkable. Over 3 years, his visual acuity gradually deteriorated to 6/9 in the right eye and 6/6 in the left eye due to cataracts. Gonioscopy and AS-OCT revealed a concave iris configuration in all four quadrants with a bend at the mid-peripheral iris (Figs. 2A and 2B).
Figure 2. Optical Coherence Tomography Images of the Anterior Chamber Angle (0° to 180°) of the Right Eye in Case 2 in (A) Dark and (B) Light Illumination Before Cataract Surgery. (C) Following Cataract Surgery, the Concave Iris Becomes Flat with Loss of Contact Between the Iris and Intraocular Lens. The Same Changes Were also Seen in Dark Lighting Conditions. The Interscleral Spur Line (ISL) Joins the Tips of the Scleral Spur.
The patient underwent an uncomplicated phacoemulsification with an IOL inserted into the bag in the right eye and then the left eye. Postoperatively, the visual acuity improved to 6/5 in both eyes with a refraction and the IOP was 16 and 14 mm Hg in the right and left eyes, respectively. Gonioscopy revealed the iris to be flat, which was confirmed by a repeat AS-OCT (Fig. 2C).
No contact between the iris and IOL was seen in both lighting conditions in all three eyes (Figs. 1C and 2C).
The development of pigment dispersion is due to pigment shedding from iridozonular contact caused by a posterior bowing of the iris. The circulating pigment settles in the trabecular meshwork, causing damage and a rise in IOP. Reverse pupil block is thought to be the pathophysiological mechanism that leads to the concavity of the iris. Pigment dispersion is associated with an iris insertion being more posterior than in normal irises,7 larger irises,8 and long anterior zonules.9 AS-OCT imaging of the iris changes following a laser iridotomy confirms previous ultrasound biomicroscopy findings.10,11 This case series illustrates the changes of the iris in patients with pigment dispersion syndrome following cataract surgery.
Although pigment dispersion can occur following cataract surgery,12 the absence of the posterior bowing of the iris following cataract surgery in the patient with preexisting pigment dispersion syndrome (Fig. 1C) suggests that the natural lens or iridolenticular contact is important in the mechanism of reverse pupil block, which can lead to the posterior bowing of a weakened iris. It is theorized that reverse pupil block occurs when small aqueous aliquots are forced into the anterior chamber when the patient blinks.13 The increased area of iridolenticular contact prevents pressure equalization between the anterior and posterior chamber, causing posterior bowing of the iris. Reverse pupil block still occurs in the presence of the iris transillumination defects because the posterior iris epithelium is still intact.14 Restoring the peripheral iris concavity to a planar configuration with either a laser iridotomy10,15 or miotic therapy5 results in a decrease in iridolenticular contact,11 which treats reverse pupil block. This causes a reduction in iridozonular contact, a decrease in pigment shedding, and further damage to the trabecular meshwork.
The changes of the iris plane following cataract surgery (Figs. 1C and 2C) show the lens contributes to the variable appearance of the iris configuration (plane or concave),3 why pigment dispersion syndrome occurs in a young age group (and not in childhood), and that this condition can “burn out” in some patients.16 In all patients, the natural lens grows in size,17 leading to the development of iridolenticular contact when the anterior surface of the lens is level with the iris insertion. As the lens size increases further, iridolenticular contact causes a normal iris to bow anteriorly due to relative pupil block, which reduces the extent of iridolenticular contact. In a weakened iris, the increase in the extent of iridolenticular contact can lead to reverse pupil block, which causes posterior bowing of the iris, iridozonular contact, and pigment shedding. The concave iris configuration can decrease over time, which may be explained by iridolenticular contact that extends to the site of iridozonular contact (due to the natural lens growth), pushing the iris anteriorly and correcting the concave configuration.18
When the patient accommodates, the pupil normally constricts and the anteroposterior diameter of the lens increases, resulting in an anterior movement of the lens and corresponding decrease in the anterior chamber depth.19 The concavity of the iris can alter due to the changes in the anterior lens curvature,20 causing an increase in the amount of iridolenticular contact leading to added reverse pupil block. This lens change may explain why an existing concave iris may worsen when the patient accommodates, as seen with ultrasound biomicroscopy. Following a laser iridotomy, the extent of iridolenticular contact decreases, which does not change with accommodation.15
The posterior bowing of the iris that leads to pigment shedding is thought to be related to an anatomical weakness of the iris. Histopathology reports shows loss of the outer epithelial cells of the iris with marked thinning of the remaining outer layers.14 In addition, an increase in both number and size of muscle fibers is reflected in a thicker radial muscle layer. It has been suggested that a gene affecting some aspect of the development of the middle third of the eye early in the third trimester is involved.8 Bovell et al.21 reported a case series of six North American families with an autosomal dominant trait, but a gene for pigment dispersion syndrome has yet to be found.
This small case series of patients with pigment dispersion syndrome imaged with AS-OCT shows the changes of the iris configuration following cataract surgery. The changes seen in different lighting conditions following cataract surgery (in the absence of a laser iridotomy) suggest that the natural lens plays an important role in the pathophysiological mechanism of this condition. The presence and extent of iridolenticular contact is needed for reverse pupil block to occur, which can cause a posterior bowing of a weakened iris. Intervention in patients with pigment dispersion syndrome with a laser iridotomy, miotic therapy, or cataract surgery can correct the concave iris configuration and decrease pigment shedding that can stabilize the IOP and reduce the risk of the development or the progression of pigmentary glaucoma.
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- Moroi SE, Lark KK, Sieving PA, et al. Long anterior zonules and pigment dispersion. Am J Ophthalmol. 2003;136:1176–1178. doi:10.1016/S0002-9394(03)00657-3 [CrossRef]
- Carassa RG, Bettin P, Fiori M, Brancato R. Nd:YAG laser iridotomy in pigment dispersion syndrome: an ultrasound biomicroscopic study. Br J Ophthalmol. 1998;82:150–153. doi:10.1136/bjo.82.2.150 [CrossRef]
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