Understanding the influence mydriatic agents may have on ocular vascular measurements is key to properly interpreting clinical results and comparing study conclusions.1 A new study published online in Ophthalmology found that a combination of topical 2.5% phenylephrine and 0.5% tropicamide in healthy eyes may cause a small, but likely clinically negligible, reduction in vessel density of the optic nerve head as seen on OCT angiography (OCT-A).

The reduction was not likely clinically significant because it was within the previously reported range of measurement variability, the researchers noted.

While no changes in macular vessel densities were detected after dilation, the team of researcher also observed small but significant increases in macular ganglion cell complex thickness in non-high density images.

The study enrolled 26 healthy participants who were about 40 years old. The researchers obtained high density and non-high density OCT-A macula and optic nerve head images at 15-minute intervals before and after dilation.

The investigators observed a small but statistically significant reduction of 0.6% in non-high density optic nerve head whole images, from a mean of 45.2% to 44.6%. A similar reduction of 0.8% was observed in the non-high density optic nerve head circumpapillary region, from a mean of 49.3% to 48.5%.

Small but statistically significant post-dilation increases in OCT-derived parafoveal ganglion cell complex thickness of approximately 0.5μm and 0.4μm (an increase of approximately 0.4% of baseline thickness in both cases) were also observed in macula 3x3mm and 6x6mm non-high density images, respectively.

The researchers found no post-dilation decreases in macular vessel density or high density optic nerve head capillary density.

To date, few studies have investigated the relationship between mydriatic agents and retinal vasculature using OCT-A in non-healthy eyes, particularly with high density scans that improve the accuracy, speed and quality of data acquisition, the researchers noted.

“Further studies should consider investigating these effects in non-healthy eyes with glaucoma and media opacities, as well as older individuals,” the researchers wrote in their paper.

Villatoro G, Bowd C, Proudfoot JA, et al. Impact of pupil dilation on optical coherence tomography angiography retinal microvasculature in healthy eyes. J Glaucoma. September 3, 2020. [Epub ahead of print].