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Pigment dispersion syndrome

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Figure 1. Peripheral iris transillumination defects in the right eye

______________________________

Dr Andrew Whatham
BOptom(Hons) DPhil GradCertOcTher

Agnes Choi
BOptom MOptom GradCertOcTher

Michael Yapp
BOptom(Hons) MOptom GradCertOcTher

Centre For Eye Health, The University of New South Wales

 

CASE REPORT

A 45-year-old Caucasian male was referred to the Centre for Eye Health for further testing in light of a family history of glaucoma (father).

Best correctable acuities were 6/7.5+2 R and L with a moderately high myopic prescription. Intraocular applanation pressures were R 20mmHg and L 18mmHg at 11 am. Corneal thicknesses at the pupil centre were thinner than average at 508 µm OD and 514 µm OS. Slitlamp examination (Figure 1) revealed peripheral iris transillumination defects in the right eye. Gonioscopy (Figures 2A and 2B) revealed open anterior chamber angles with the level of pigmentation in the pigmented trabecular meshwork being dense in the right eye and moderate in the left, in particular inferiorly. Stereoscopic optic nerve assessment (Figures 3A and 3B) showed average-sized discs with no significant peripapillary atrophy and no evidence of Drance haemorrhages.

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Figure 2A. Dense pigmentation in the pigmented trabecular meshwork in the right eye

Figure 2B. Moderate pigmentation in the pigmented trabecular meshwork in the left eye

The neuroretinal rim (NRR) showed superior shelving in both eyes being more pronounced in the right. The right NRR also showed focal thinning inferiorly. A superior and an inferior wedge retinal nerve fibre layer (RNFL) defect were also noted in the right eye (Figure 4). Fundus examination was otherwise unremarkable in each eye.

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Figure 3A. Large optic nerve cupping and thin neuroretinal rim in the right eye

Figure 3B. Left optic nerve showing smaller cupping and thicker neuroretinal rim

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Figure 4. Superior and inferior wedge RNFL defects in the right eye

Cirrus OCT RNFL analysis (Figure 5) showed the average RNFL thickness to be borderline in the right eye and within normal limits in the left; however, the superior and inferior RNFL quadrants in the right eye were classified as outside normal limits.

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Figure 5. Superior and inferior RNFL quadrants OD classified as outside normal limits and the 6 o’clock RNFL sector OS as borderline on Cirrus OCT

Humphrey 24-2 threshold SITA Standard perimetry (Figures 6A and 6B) revealed adjacent points of reduced sensitivity infero-nasally and superiorly in the right eye and an essentially normal visual field in the left eye. Considering the clinical appearance is consistent with pigmentary dispersion glaucoma and the complicated nature and relatively high progression rate of this type of glaucoma, the patient was referred to a glaucoma specialist ophthalmologist for further assessment.

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Figure 6A. Visual field examination showed reduced sensitivity inferiorly in the right eye

Figure 6B. Left eye showed an essentially normal visual field

Discussion

Pigment dispersion syndrome (PDS) is characterised by two or more of iris transillumination, pigment deposition on the central corneal endothelium (Krukenberg spindle) and increased pigmentation of the trabecular meshwork.1 Pigmentary ocular hypertension (POH) refers to the co-existence of PDS with elevated IOP but without glaucomatous optic neuropathy. The term pigmentary glaucoma (PG) refers to PDS in conjunction with glaucomatous optic neuropathy.

PDS is typically bilateral but can be asymmetric.2,3 PDS classically affects young Caucasians between 30 and 50 years of age with myopia4 but all ethnicities can be affected. Men and women appear equally likely to develop PDS, although males appear much more likely to convert to PG.2,5

In newly diagnosed eyes with PDS, conversion rate to PG has been estimated to be 10 per cent at five years after diagnosis and 15 per cent at 15 years after diagnosis.4 Risk factors for increased likelihood of conversion from PDS to POH and PG include male gender, higher myopic refractive error, presence of a Krukenberg spindle and higher IOP.2

Iris transillumination defects arise from loss of pigment from contact between the posterior iris pigmented epithelium and the lens zonules; however, they are not always present or of this form in individuals with PDS.6

Specific anomalous anatomical relationships between the iris and lens are believed to give rise to release of pigment from the posterior iris. In particular, the phenomenon of reverse pupil block has been postulated. This is believed to arise from differential pressure in the anterior and posterior chambers so that the higher anterior chamber pressure bows the peripheral iris posteriorly (increasing iris concavity) with the area of irido-lenticular contact acting as a one-way valve preferentially allowing aqueous flow from the posterior to anterior chamber and inhibiting flow in the reverse direction. The consequence of this is that the iris posterior pigmented epithelium comes into contact with the lens zonules, which abrade the epithelium, leading to pigment release into the aqueous.

Research with anterior OCT and ultrasound biomicroscopy has shown that accommodation, Pilocarpine 2% and laser peripheral iridotomy7,8,9 can eliminate the iris concavity. Alternatively, exercise has been shown to show a significant increase in iris concavity in both eyes with and without pigment dispersion.10

Pigmentation on the corneal endothelium is frequently present in a vertical spindle formation, referred to as Krukenberg’s Spindle. This particular pattern of pigment distribution is believed to arise as a consequence of the direction of aqueous convection currents in the eye.2,11

Increased trabecular meshwork pigmentation, visualised during gonioscopy, is a prominent characteristic of PDS and the most relevant when considering glaucoma risk. The released iris pigment travels to the anterior chamber angle via the aqueous convection currents and is phagocytosed by the trabecular endothelial cells. The trabecular endothelial cells readily phagocytose pigment, and provided the pigment load is not excessive, the architecture of the trabecular meshwork remains undisturbed.11 Histological characteristics of a small group of eyes with PDS, POH and PG showed that PG seems to occur when the excessive pigment in the anterior chamber angle results in loss of normal trabecular architecture, increasing outflow resistance.12

A number of reports have shown PG ‘burnout’ with increasing time, in which pigment dispersion is no longer active, IOP normalises and progressive optic neuropathy is halted.2 The reason for this may be that as the eye’s crystalline lens continues to grow throughout life, iris profile changes and reverse pupil block is no longer an issue. As such, new pigment dispersion no longer occurs. If the trabecular meshwork is relatively undamaged, optic nerve health may be stable; however, if the trabecular meshwork has become irreversibly damaged, progressive optic nerve damage may continue to occur with or without normalisation of IOP.2

 

  1. Balidis MO, Bunce C, Sandy CJ, Wormald RP, Miller MH. Iris configuration in accommodation in pigment dispersion syndrome. Eye (Lond) 2002; 16: 694-700.
  2. Niyadurupola N, Broadway DC. Pigment dispersion syndrome and pigmentary glaucoma—a major review. Clin Experiment Ophthalmol 2008; 36: 868-882.
  3. Yip LW, Sothornwit N, Berkowitz J, Mikelberg FS. A comparison of interocular differences in patients with pigment dispersion syndrome. J Glaucoma 2009; 18: 1-5.
  4. Siddiqui Y, Ten Hulzen RD, Cameron JD, Hodge DO, Johnson DH. What is the risk of developing pigmentary glaucoma from pigment dispersion syndrome? Am J Ophthalmol 2003; 135: 794-799.
  5. Lascaratos G, Shah A, Garway-Heath DF. The Genetics of Pigment Dispersion Syndrome and Pigmentary Glaucoma. Surv Ophthalmol 2013; 58: 2: 164-175.
  6. Qing G, Wang N, Tang X, Zhang S, Chen H. Clinical characteristics of pigment dispersion syndrome in Chinese patients. Eye (Lond) 2009; 23: 1641-1646.
  7. Aptel F, Beccat S, Fortoul V, Denis P. Biometric analysis of pigment dispersion syndrome using anterior segment optical coherence tomography. Ophthalmology 2011; 118: 1563-1570.
  8. Liu L, Ong EL, Crowston J. The concave iris in pigment dispersion syndrome. Ophthalmology 2011; 118: 66-70.
  9. Potash SD, Tello C, Liebmann J, Ritch R. Ultrasound biomicroscopy in pigment dispersion syndrome. Ophthalmology 1994; 101: 332-339.
  10. Jensen PK, Nissen O, Kessing SV. Exercise and reversed pupillary block in pigmentary glaucoma. Am J Ophthalmol 1995; 120: 110-112.
  11. Campbell DG, Schertzer RM. Pathophysiology of pigment dispersion syndrome and pigmentary glaucoma. Curr Opin Ophthalmol 1995; 6: 96-101.
  12. Gottanka J, Johnson DH, Grehn F, Lutjen-Drecoll E. Histologic findings in pigment dispersion syndrome and pigmentary glaucoma. J Glaucoma 2006; 15: 142-151.


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