Her IOP measured 19mm Hg OD and 22mm Hg OS. Her central corneal thickness was 549µm OD and 558µm OS. Biomicroscopically, she exhibited a distinct Krukenberg spindle on the back surface of each cornea, as well as rare mid-peripheral iris transillumination defects OU.
Gonioscopically, there was a classic appearance of pigment dispersion syndrome with dense trabecular meshwork pigmentation and evidence of Sampaolesi’s line in both eyes. Notably, the iris had a concave configuration with significant backward bowing.
Her optic nerves appeared healthy, with robust, symmetrical neuroretinal rims. Optical coherence tomography showed a normal retinal nerve fiber layer in both eyes. Additionally, threshold perimetry was normal OU.
We diagnosed her with pigment dispersion syndrome (PDS) and low-risk ocular hypertension. After discussion and education, we decided to monitor her on a periodic basis without medical therapy. But, because she had classic PDS without glaucoma, could we do anything to reduce the amount of pigment being liberated and possibly prevent glaucomatous development?
Laser peripheral iridotomy (LPI) has been advocated as a means of changing the iris approach and reducing pigment liberation. In this month’s column, we discuss PDS and pigmentary glaucoma, as well as address the potential therapeutic benefits of LPI.
PDS and Pigmentary Glaucoma
Patients with PDS and pigmentary glaucoma experience iris pigment liberation within the anterior chamber. Often, this is seen as a diffuse accumulation or possibly a granular, brown vertical band located along the corneal endothelium, which is known as a Krukenberg spindle. Pigment accumulation also may be evident on the lens or iris surface, within the trabecular meshwork and on Schwalbe’s line (where it is referred to as Sampaolesi’s line). Radial, spoke-like transillumination defects of the mid-peripheral iris are common.1,2
Many patients with PDS and pigmentary glaucoma demonstrate a concave iris approach as it inserts into the anterior chamber angle, yielding a “backward bowed” appearance on gonioscopy. This change places the posterior iris into apposition with the lens zonules. As the iris responds to light, iridozonular friction results in pigment liberation from the posterior iris, which follows the flow of the aqueous convection current into the anterior chamber angle.1,2
Heavy trabecular meshwork pigment and concave iris in a young female with PDS.
It has been theorized that in cases with a markedly concave iris insertion, the iris functions as a flap valve lying against the anterior lens surface. The iris is forced backwards when a pressure gradient develops that is greater in the anterior chamber, closing the valve and trapping the aqueous from moving into the anterior chamber. This increased anterior chamber pressure subsequently forces the iris into the aforementioned concave approach, which is termed “reverse pupillary block.”3-7
There are two possible consequences of excessive pigment accrual. First, pigment may reside benignly in the trabecular meshwork where IOP is unaffected and the condition remains PDS. Alternately, the IOP rises due to a breakdown of normal phagocytic activity of the endothelial cells and subsequent loss of normal trabecular architecture and function, and pigmentary glaucoma develops.8-10
LPI to the Rescue?
Laser peripheral iridotomy often is considered and recommended for PDS and pigmentary glaucoma patients who exhibit significant iris concavity. Clinical researchers have clearly demonstrated that the iris can convert from a concave to a planar approach following LPI.11-13 For this reason, LPI has been recommended as a method to reduce melanin release and pigment deposition in the trabecular meshwork.14
The popularity of LPI for eyes with PDS and pigmentary glaucoma seems to be cyclical. The procedure was commonly performed for some time and then abandoned. Today, it appears that LPI is again being done in PDS and pigmentary glaucoma to some extent––but the benefit in overall IOP management, as well as the risk reduction for visual disability, is unclear.
In 2005, the results of a retrospective analysis shed some light on the role of LPI in the management of patients with pigmentary glaucoma. Retrospective data was analyzed on patients with bilateral pigmentary glaucoma, who had received uniocular LPI. The main outcome measure was the post-laser intraocular pressure course of the treated eyes, compared with the fellow, untreated eyes.
The study included 46 patients who had been observed for two or more years.15 Among the patients observed for less than two years, the mean intraocular pressure in the LPI-treated eyes increased slightly compared with the fellow, untreated eyes. Among the patients observed for two or more years, the mean intraocular pressure in the LPI-treated eyes decreased by approximately 2mm Hg over that seen in the untreated fellow eyes; however, subsequent analysis showed that a higher mean baseline intraocular pressure in the treated eyes accounted for the apparent treatment effect of LPI.
Clearly, there were many limitations to this study––most notably, a lack of controls and a standardization of methodology. The authors concluded that LPI does not effectively provide long-term IOP control in eyes with pigmentary glaucoma, but that a large, prospective trial was still warranted to determine whether LPI holds any potential therapeutic benefit for such patients.15
Then, in 2011, a prospective, controlled, randomized study looked 166 eyes with pigment dispersion syndrome and elevated IOP, but no glaucomatous damage, and randomized eyes to either LPI or no LPI. The primary outcome was conversion to pigmentary glaucoma at three years. Secondary outcome measures were whether eyes required topical glaucoma medications during the study period and the time to conversion or medication intervention.
During the study, 15% of eyes in the LPI group converted to glaucoma, compared to 6% of eyes in the control group. The proportion of eyes started on medical treatment was similar between the two groups. The researchers also documented no difference in time to visual field progression or topical therapy initiation between the treatment and control groups.
The authors concluded that LPI did not help limit or prevent disease progression from PDS with associated ocular hypertension to pigmentary glaucoma within three years of follow-up.16
While acknowledging a lack of clinical evidence that LPI has a long-term effect in preventing glaucoma in eyes with pigment dispersion syndrome, a more recent report suggested that the procedure should only be undertaken in patients younger than 40 years, if the mid-peripheral iris shows backward bowing, and if the intraocular pressure is normal or slightly increased with no progressive signs of optic nerve damage.17
So, in 2014, where does LPI stand with regard to the management of patients with PDS and/or pigmentary glaucoma? It’s still not clear. While the procedure can change the anatomic configuration of the iris and theoretically help reduce pigment liberation and accumulation within the trabecular meshwork, there is no compelling evidence to suggest that LPI is beneficial in reducing IOP or preventing pressure elevation in this disease. For this reason, we do not advocate LPI for those with pigment dispersion syndrome or pigmentary glaucoma.
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