Properties of new diffusion filters for treatment of amblyopia with accurate occlusive effects

Our purpose is to present the characteristics of newly developed diffusion filters that can reduce the best-corrected visual acuity (BCVA) of the non-amblyopic eye to a specified value and that can be used to treat amblyopia.

Silica sol is a colorless and transparent colloidal gel of different particle sizes. The silica was added to an emulsion adhesive, thoroughly mixed, and coated evenly on polyethylene terephthalate films. Twelve filters with 12 different concentrations of silica were constructed. The density of the silica particles on the films was determined by scanning electron microscopy, and the haze values and light transmittance were measured with a goniophotometer. The reduction of the BCVA by the filters was determined in 16 healthy young women (mean age, 22.0 ± 2.3 years) by attaching the filters to spectacles.

Scanning electron microscopy showed a monolayer of evenly spaced silica particles. The haze values of the 12 filters were related to the concentration of silica. The total light transmittance of the 12 filters was not significantly correlated to the concentration of silica. The BCVAs measured with the 12 filters were significantly and inversely correlated with the concentration of silica for both eyes (right eye, y = 0.174x - 0.197, R(2) = 0.951; left eye, y = 0.173x - 0.212, R(2) = 0.983).

These findings indicate that these diffusion filters can reduce the BCVA with no reduction of light transmittance. We conclude that they can be used to degrade the image of the dominant eye by known amounts in patients with amblyopia without affecting the overall light levels to the eye, i.e., form deprivation without light deprivation.