Clinical profile and demographic distribution of pigment dispersion syndrome: An electronic medical record-driven big data analytics from an eye care network in India

INTRODUCTION

Pigment dispersion syndrome (PDS) has features of iris pigment dispersion all over the eye with or without raised intraocular pressure (IOP).^[1] The first case of PDS was described in 1940 by Sugar.^[2] He went on to further report the features of PDS and pigmentary glaucoma (PG), in two cases and further strengthened the association of the risk for glaucoma in the presence of dense pigmentation in the trabecular meshwork,^[3] with the origin of the pigment being the iris.^[4] The features of Krukenberg’s spindle on the corneal endothelium, mid peripheral iris transillumination defects, deep anterior chamber, dense pigmentation of the trabecular meshwork on gonioscopy and increase in IOP (especially post mydriatic use), with associated myopia were first described here.^[3] The added features are the concave configuration of the peripheral iris on gonioscopy^[5] and the more posterior insertion of the iris, confirmed on ultrasound biomicroscopy (UBM).^[6] Zentmayer first described a ring of pigments on the posterior capsule of the lens, later known as Zentmayer’s line^[7] or Scheie’s and Cameron stripe^[8] and the pigmentation of the Schwalbe’s line is known as Sampaolesi line.^[9] Initially thought to be a very rare disease, the prevalence of PDS has increased, due to better diagnostic capabilities and increased awareness, with demographic studies helping us to understand it’s distribution. There is, however, a paucity of literature on the prevalence and demographic distribution of PDS in the Indian population. The purpose of the study is to present the clinical and demographic profile of PDS at a large multi-tier ophthalmology network in India using electronic medical record-driven analytics.

MATERIAL AND METHODS

RESULTS

Age

The mean age of the patients was 46.92 ± 14.23 years, while the median age was 46 (IQR: 36–56) years. The most common age group of the patients were distributed between 31 and 40 years (n = 100; 24.81%) followed by 41 and 50 years (n = 94; 23.33%). The distribution of patients in each age-decade is presented in [Figure 1].

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Figure 1:

Decade-wise distribution of patients with pigment dispersion syndrome.

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DISCUSSION

This study sought to describe the clinical profile and demographic distribution of PDS in a large cohort of patients presenting to a multi-tier hospital network in India using electronic medical records-driven big data analytics. The primary purpose of the study was to determine the relative proportion and demographic profile of PDS in the clinical care setup. The diagnosis of PDS is most often clinical with the clinical findings having wide variations, making PDS an underdiagnosed and misdiagnosed condition.^[17] In challenging cases with a high degree of doubt, the diagnosis can be clenched with the use of UBM^[18] or anterior segment optical coherence tomography.^[19] The overall prevalence of PDS was 0.014% of all eye diseases diagnosed between 2010 and 2021 (11-year period). In other studies, a prevalence of 2–4%^[1,20] shows that PDS has a higher prevalence among Caucasians as compared to non-Caucasians.^[21,22] The most probable reason being the denser pigmentation of the irides which may conceal iris transillumination defects in non-Caucasians. In the US, the prevalence is 2.5% and the incidence is 4.8/100000 population/year.^[23] A study involving subjects who were consulting for refractive surgery showed a higher prevalence of 25.9%, although the bias here may be due to the higher number of myopic subjects.^[24]

The “Burn out phase” is the phase which is said to occur approximately 10 years after the onset of the disease and is characterised by a lowering of IOP and stabilisation of the glaucomatous damage. The hypothesis behind this being the enlargement of the anteroposterior diameter of the lens with an increase of distance between the iris and zonular fibres and reduction in pigment release.^[1] This finding seems to be true in the Indian population as well, as seen by the decreasing incidence with age in our data. Mean age at diagnosis of PDS for Caucasian men is 40–50 years.^[1] Males were seen to be diagnosed with PDS about 3 times more than females and at younger age correlating with the findings in this present study,^[3,25] although some studies state equal prevalence in both.^[5,8] Possible protective effect of sex hormones, progesterone and oestrogen, in increasing outflow facility have been implicated in this difference, but further studies have not been conducted.^[26,27] Krukenberg’s spindle was however found more in males in our study, contradicting the findings by Duncan.^[26]

The disease is predominantly bilateral asymmetry which is often noted, with the worse affected eye having more pigment deposition.^[1,28] A higher incidence in the higher SE strata and urban population in our study may be attributed to better awareness about the need for frequent ophthalmic checkups in this section of society.

Myopia >−1.00 D has been noted in almost 38–100% of cases in other studies.^[8,28] In our study, myopia was present in 208 eyes, (28.93%). Lattice degeneration was frequently found in PDS at the rate of 20%^[29] and 33.3%^[30] and retinal breaks were found at an incidence of 12%.^[29,31] Retinal detachments occur at a rate of 6.6% irrespective of pilocarpine use, although most clinicians caution against its use.^[8,32] In our set of patients, lattice degeneration and retinal detachment were however found to be lower as compared to the previous studies. Some authors have hypothesised that a genetic link exists between myopia, pigment dispersion and dystrophic retinal changes in patients having all these manifestations.^[8] Further studies would be required to confirm or refute this.

Iris transillumination defects have been reported in about 86% of cases,^[23] more so in Caucasian eyes. It has also been noted that the more the pigment dispersion, the more the magnitude of iris transillumination and Krukenberg’s spindle size.^[33] The comparatively less incidence of iris transillumination defects in our patients could be attributed to the thick highly pigmented irides in Indian eyes. Detection can however be improved in patients with thick and highly pigmented irides by the use of infrared imaging.^[34]

The grade of pigmentation of the trabecular meshwork is said to be higher in cases with higher IOP and more severe glaucoma.^[35,36]

Prostaglandin analogues do not have any particular anti-PDS effects per se but their mechanism of action of increased uveoscleral outflow seem to be advantageous in such patients with studies showing it to be more efficacious than timolol.^[37] There is no evidence that they can increase pigment dispersion.^[38] They were the most prescribed medication in our set of patients. In terms of mechanism of action, pilocarpine would seem to be the ultimate management strategy for PDS and PG as it reduces the posterior bowing of the iris, checks pupil dilatation and diminishes the exercise induced rise in IOP.^[12,39,40] Its poor tolerability among patients, in the form of the general side effects, along with ocular effects such as accommodative spasm, risk of cataract and retinal detachment, however, has limited its use.^[41]

Laser peripheral iridotomy (LPI) is still a controversial mode of treatment for PDS and PG. It was first advocated by Campbell^[12] after the concept of reverse pupillary block gained momentum.^[42] LPI is not the mainstay in the management of PDS and PG as it is not successful in all eyes,^[43] especially in those eyes that have advanced and permanent damage to the trabecular meshwork.^[44] A few randomised trials have failed to show any benefit of LPI in preventing progression of PDS with high IOP to PG.^[45,46] YAG peripheral iridotomy was documented in 100 eyes (12.94%) in our study.

Selective laser trabeculoplasty (SLT) as a treatment modality can be tried in PDS and PG, but cases of considerable increase in IOP requiring trabeculectomy have been reported.^[47] Hence, awareness of this possible sustained IOP spike is needed and close follow-up required. No SLT was performed in our patients.

CONCLUSION

This study aimed to describe the epidemiology and clinical presentation of PDS and PG in 2.9 million new patients presenting to a multi-tier ophthalmology hospital network in India. The findings show that PG is more common in males presenting during the fourth decade of life and is predominantly bilateral. A third of the eyes have raised IOP and a tenth of them are affected with blindness at presentation.