Phentolamine Mesylate Eye Drops for Severe Dim Light Vision Disturbances

By Patrick Daly - October 19, 2022

In a recent randomized clinical trial in BMC Ophthalmology, researchers explored the potential of 1.0% phentolamine mesylate ophthalmic solution (PMOS) to improve vision and image quality among patients with dim light vision disturbances (DLD), which encompasses vision symptoms such as glare, halos, and starbursts in low illumination settings. According to the study’s lead author, Jay Pepose, PMOS was well tolerated, reduced pupil size, and improved contrast sensitivity and visual acuity in adults with severe DLD.

This exploratory trial enrolled 24 patients with severe DLD, defined as severe night vision impairment that was not improved by distance spectacles and a score of ≥0.3 log units below the normal contrast sensitivity range with glare at 2 or more spatial frequencies. The primary efficacy end points were pupil diameter change from baseline, contrast sensitivity, and visual acuity, and the primary safety end poitns were intraocular pressure, conjunctivv al hyperemia, and systemic effects.

Exploratory PMOS Eye Drops Improves DLD Symptoms in Adults

The participants were randomized 2:1, with 8 patients receiving placebo (63% female, median years of age, 47) and 16 receiving PMOS (75% female, mean years of age, 42). The researchers reported that PMOS significantly decreased the pupil diameter by a mean of -1.3 mm (range, 0 to -2.8 mm; P≤.03) in the study group. Additionally, PMOS improved participants’ number of letters read in mesopic and photopic high- and low-contrast visual acuity (LCVA).

Notably, compared with the placebo group, significantly more patients in the PMOS group achieved mesopic LCVA 5 letter (69% vs 31%; P=.029) and 10 letter (34% vs 6%; P=.04). A greater proportion of patients in the PMOS group also registered 15 letters (19% vs 0%; P=.16), though the difference was not statistically significant. Lastly, the researchers noted that the only side effect observed was a mild increase in conjunctival hyperemia.

The report noted the study was limited by a small sample size, which prevented the authors from performing subgroup analyses, and by only measuring changes from baseline at 1 timepoint, preventing any analysis of the function of PMOS on DLD over time. The researchers also suggested that, as this study was performed in a controlled environment, it may be useful to explore real-world conditions, such as night driving.

“PMOS could be a viable and safe therapeutic option for DLD patients with various eye conditions that cause photic phenomena and decreased mesopic vision,” the authors summarized, and suggested that “looking at regulatory approval pathways for a new DLD indication, the use of mLCVA versus contrast sensitivity as a primary endpoint would be more applicable and more standard for clinical trials.”

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