Simulation of panretinal laser photocoagulation using geometric methods for calculating the photocoagulation index.

PURPOSE

To establish geometrically based methods for simulating panretinal laser photocoagulation (PRP) for the photocoagulation index.

METHODS

A formula for calculating the curved surface area of a spherical dome was used for the simulation. If the radius of the dome is c and the height of the dome is h, then the curved surface area (S) of the dome is S = π (c2 + h2). We calculated the area of the whole retina using this formula and the anatomical dimensions of the standard eyeball. To simulate PRP with a 400-μm spot on the retina with 1-spot spacing, we drew 400-μm-diameter circles, separated by 400 μm, on a retinal map. We calculated the ratio of the total retinal photocoagulated area to the whole retina, termed the photocoagulation index, in order to investigate the impact of the extent of the photocoagulated area and the pulse duration on PRP.

RESULTS

The whole retinal area was 1,092 mm2. The numbers of spots in the scattered and full-scattered PRP were 1,222 and 1,814, respectively. The photocoagulation index was 14.1% and 20.9% for scattered and full-scattered PRP, respectively. These values changed to 14.3% (5.6%) and 21.3% (8.3%), respectively, for PRP with a 100-ms pulse or a 20-ms pulse.

CONCLUSIONS

This method will be useful for investigating the impact of various PRP parameters (duration, spacing, intensity of burns, extent of photocoagulated area, etc.) on the photocoagulation index.