OcuTOP: a novel handheld corneal topography device with misalignment correction

This study aimed to develop and validate OcuTOP, a novel handheld corneal topography device designed to overcome the limitations of conventional desktop systems. By incorporating software-based misalignment correction, OcuTOP seeks to provide accurate corneal curvature measurements without need for bulky mechanical alignment mechanisms. Validation was performed using a reference surface with known geometry to assess device accuracy and robustness.

The OcuTOP device (75 g; 85 × 60 × 60 mm) was evaluated using a reference button with a known curvature (43.3 D). Controlled misalignments were introduced in longitudinal (Z: 42.5-43.5 mm), lateral (X: ±2 mm), and vertical (Y: ±2 mm) directions, generating 243 test cases. Images acquired by the device were analysed using neural network algorithms to estimate misalignment parameters, which were subsequently used to correct axial and tangential curvature maps and estimate button diameter, analogous to white-to-white corneal diameter.

OcuTOP demonstrated strong agreement with reference curvature values across all misalignment conditions (P for K1 & K2 = 0.365, 0.385 at Z = 42.5 mm; 0.606, 0.907 at Z = 43.0 mm; 0.297, 0.462 at Z = 43.5 mm). Even at maximum displacement (±2 mm in X and Y), central curvature predictions remained within 2% of true values, with mean astigmatism artifacts limited to <0.2 D at the apex of the surface. However, the errors in estimating curvature values increased progressively towards the periphery. Neural network estimation of Z distance achieved a mean error of 0.06 ± 0.05 mm, with no significant influence on the ability of the device to estimate curvature. WTW predictions were also consistent, with a mean value of 11.66 mm, differing by <1.5% from the reference diameter.

OcuTOP's software-based correction reliably compensates for translational and longitudinal misalignments, showing promising results for future studies enabling accurate corneal surface measurements without mechanical stabilisation.