# Characterizing Visual Field Defects with Tangent Screen Perimetry in Organic Versus Non-Organic Pathologies

## TL;DR

This study shows that tangent screen perimetry can help distinguish between real and fake visual field loss by analyzing specific patterns and ratios.

## Contribution

The study characterizes distinct tangent screen patterns and ratios specific to functional versus organic visual field loss.

## Key findings

- Clover leaf and reversal patterns were observed in functional cases but not in organic cases.
- Functional visual loss was associated with younger age, specific patterns, and lower tangent ratios.
- Tangent screen perimetry effectively differentiates functional from organic visual field loss.

## Abstract

Background/Objectives: Tangent screen perimetry is a valuable tool for detecting functional visual loss (FVL), which is suspected when the visual field fails to expand as expected with distance. However, there is currently a lack of research documenting the specific tangent screen patterns produced by patients with organic visual loss (OVL), defined as visual field loss caused by identifiable structural or neurologic pathology. This study aims to characterize the visual field patterns observed in patients with organic and functional pathologies during tangent screen perimetry and evaluate its diagnostic efficacy in confirming FVL. Methods: Medical records of patients from Seoul National University Bundang Hospital between August 2009 and August 2019 were reviewed. All subjects underwent a comprehensive neuro-ophthalmologic examination with additional testing to confirm the diagnosis of OVL or FVL. A total of 126 eyes from 76 patients exhibiting visual field constriction within 30 degrees were included. The tangent ratio (TR) was defined as the average visual field (in radians) at a far distance (e.g., 2 m) divided by the average visual field at a near distance (e.g., 1 m). The visual field patterns and TR were analyzed, and the diagnostic value of TR in detecting FVL was determined. Results: The clover leaf pattern and reversal pattern were observed in 8.8% and 12.7% of FVL cases, respectively, whereas no such patterns were found in OVL cases (p = 0.002, p < 0.001). The TR varied from 0.50 to 1.06 (mean 0.77 ± 0.16) in OVL and from 0.33 to 1.03 (mean 0.65 ± 0.15) in FVL (p < 0.001). Younger age, a clover leaf pattern or reversal pattern on tangent screen perimetry, and a lower TR were significantly associated with FVL. Conclusions: Tangent screen perimetry is an effective adjunct for differentiating functional from organic visual field loss, particularly in cases of visual field constriction.