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Editors Selection IGR 11-4

Medical Treatment: Prostaglandins and SLT

Comment by Jay Katz on:

24956 Topical prostaglandin analogues do not affect selective laser trabeculoplasty outcomes, Singh D; Coote MA; O'Hare F et al., Eye, 2009; 23: 2194-2199

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The influence of previous and continued prostaglandin (PG) therapy on the response to 180 degree selective laser trabeculoplasty (SLT) was investigated by Singh et al. (1627) in a retrospective study of 123 patients. There were 74 patients on PG treatment and 49 not on PG. The primary success measure was a 20% IOP reduction at six months. No statistical differences were noted: (1) in the mean IOP reduction of 3.9 (PG group) vs. 4.6 mmHg (no PG group); and (2) in the 20% IOP reduction with 39% (PG group) vs. 45% (no PG group).

A number of interesting aspects emerged from this study. (1) 'To reduce influence from regression to the mean' the authors averaged the three prior IOP measurements from the previous three months to provide a 'pre-laser' baseline IOP. This may have lowered the observed reduction in IOP after SLT. (2) A higher pre-laser IOP was predictive of a successful response (odds ratio = 1.12). Although not statistically significant, there was a higher baseline IOP in the PG group 20.9 vs. 19.8 mmHg in the no PG group. (3) In the subgroup analysis eyes on monotherapy with a non-PG drug had a mean IOP lowering of 6.2 vs. 3.9 mmHg for the PG monotherapy group. Also, patients on no glaucoma medication achieved only a 4.3 mmHg IOP reduction. Prior trials reported a 6-8 mmHg IOP drop after primary SLT. The disparity may be due to: only 180 degrees of SLT application and a lower starting IOP in the Singh study.

The important message imparted is that SLT may be clinically helpful in patients using PG analogues. However, there still remain fundamental questions such as: do prostaglandins and SLT lower IOP by similar mechanisms of action?

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