A spreadsheet-based algorithm for objective assessment of depth of focus from defocus curves

To describe and clinically evaluate a spreadsheet-based algorithm for reproducible depth-of-focus (DoF) calculation, incorporating rule-based continuity detection derived from defocus-curve topology.

Humanitas Clinical and Research Center, Rozzano, Milan, Italy.

Methodological description with retrospective clinical validation.

The algorithm identifies dioptric crossings of a predefined logMAR threshold by locating bracketing points and applying linear interpolation. Validation involved analyzing defocus curves (-4.0 to +1.5 D in 0.50-D steps) from monofocal pseudophakic eyes and comparing automated results with manual measurements by two experienced operators. Logic was implemented to classify continuous and discontinuous (multimodal) profiles and flag out-of-range data.

Thirty pseudophakic eyes implanted with monofocal intraocular lenses were included. Depth of focus ranged from 1.10 to 3.17 D (mean 1.92 ± 0.47 D). Agreement between the algorithm and the two operators was high, with mean differences of -0.01 D (SD 0.08) and 0.00 D (SD 0.05), respectively. The inter-operator difference was 0.01 D (SD 0.09). Mean absolute error was <0.05 D. Bland-Altman limits of agreement versus the operators' mean ranged from -0.10 to +0.09 D.

The proposed method ensures objective and reliable DoF quantification by minimizing subjective interpretation and manual workload. While clinical validation focused on monofocal profiles, the topology-based continuity logic provides a structured approach for analyzing complex curve profiles. A template spreadsheet is provided for implementation.