Driving in the Dark: Fuchs’ Patients Have Reduced Nighttime Vision Despite Normal VA

Using the National Advanced Driving Simulator, a small study showed that patients with Fuchs’ dystrophy had shorter hazard detection distances under glare conditions (i.e., headlights) than controls without the disease. Photo: Christine Sindt, OD. Click image to enlarge. As one of the many daily activities affected by Fuchs’ endothelial corneal dystrophy (FECD), patients may report concerns about their ability to safely drive at night despite having normal standard measures of vision. To better understand this discrepancy, researchers recently performed a small study that used the National Advanced Driving Simulator (NADS) to investigate the impact of FECD on nighttime driving performance, particularly focusing on the effects of glare from oncoming headlights. The six included patients—all of whom had normal visual acuity (VA) and contrast sensitivity—experienced significant impairments in recognizing roadside hazards during nighttime driving simulations.To conduct the pilot study, the researchers matched the six Fuchs’ patients with an equal number of age-matched controls. Participants underwent Snellen VA testing, Mars contrast sensitivity assessment and Scheimpflug tomography to evaluate corneal health. Participants were subjected to three driving scenarios in the NADS MiniSim, designed to replicate nighttime driving with different levels of glare: "variable glare," where glare intensity fluctuated, "constant glare," and "no glare." The results, published last week in Cornea, showed that patients with FECD recognized 14% fewer hazards under variable glare conditions compared to controls, with scores of 81.8% vs. 95.8%. They required being nearly twice as close to roadside hazards to recognize them—76.5 feet vs. 137.7 feet for controls. Despite having approximately 20/20 Snellen VA, patients demonstrated poor driving performance associated with tomographic measures of subclinical corneal edema and abnormal corneal densitometry.A thicker central corneal thickness and higher anterior densitometry values were linked to shorter hazard detection distances under glare conditions. Additionally, abnormal posterior densitometry showed a strong negative correlation with hazard recognition scores.Interestingly, the study authors also found that variable glare reduced driving performance more than constant glare, which they suggested in their paper “may be because of the pinhole effect caused by constant glare—that is, a miotic pupil may help the driver see ‘through’ the constant glare compared with a pupil that is intermittently mydriatic and miotic.”While more research is required to assess the impact of Fuchs’ on nighttime driving performance, given this study’s small sample size, the researchers pointed out, “This is the first functional assessment of patients with FECD in a driving simulator that measures nighttime disability from glare.” They concluded, “Clinicians should know that even with normal 20/20 Snellen VA and normal logCS, patients with FECD performed significantly worse than controls,” while also reiterating the observed correlation “between nighttime driving disability and tomographic markers of subclinical corneal edema and abnormal corneal densitometry.”Click here for the journal source. Sarin SR, Kigin M, Balk E, et al. Functional assessment of FECD in the national advanced driving simulator: initial study of nighttime glare and Scheimpflug imaging. Cornea. May 23, 2025. [Epub ahead of print].