Visual Distortion Test Shows Promise for Monitoring Keratoconus

Measuring visual distortion may provide clinicians insight into the early development and severity of progressive keratoconus, according to research published in Eye. 

“The commonly used clinical vision tests, such as visual acuity and contrast sensitivity, may not reflect the symptoms experienced in keratoconus and there are no quantitative tools to measure visual distortion,” researchers explain. In the study, the researchers utilized a quantitative test based on vernier alignment and field matching techniques to quantify visual distortion in keratoconus and evaluate its association with corneal structural changes.

The study included 25 participants (mean age, 29.84±7.46 years, 15 women) with keratoconus at different disease stages and 25 normal-sighted controls (mean age, 22.12±2.62 years, 17 women). In the experiment, participants aligned supra-threshold white target circles in opposite fields in reference to guidelines as well as circles to complete a square structure monocularly and repeated the task 5 times. Researchers calculated the global distortion index (GDI) and global uncertainty index (GUI) as the mean and standard deviation respectively of local perceived misalignment of target circles across 5 trials. 

Both GDI and GUI were higher in eyes with keratoconus compared with normal eyes (P <.01). Both distortion indices correlated with the best corrected visual acuity, maximum corneal curvature (K_max), topographical keratoconus classification and central corneal thickness, according to the report.   

“This study for the first time quantitatively evaluated visual distortion experienced in keratoconus,” according to the researchers. “In future, the distortion test could be developed as a home-based tool to monitor keratoconus.” 

Study limitations include its cross sectional design and inability to provide a systematic method for identifying significant change in the shape of the constructed square.