Computational Model of Sclerotic Scatter.

PURPOSE

A clinical examination technique to detect pathology within the anterior eye is known as "sclerotic scatter" (SS). Its propagation pathway has not been thoroughly investigated. Although conventionally theorized to occur by "total internal reflection" (TIR) within the cornea, existing data suggest that this may be an incomplete explanation.

METHODS

An anterior eye model representative of a human eye has been constructed using nonsequential ray tracing (OpticStudio 18.1). Three generations of the model were constructed to support the analyses of the pathway of light in SS. A design of experiment methodology involving the key parameters was used to determine the slit-lamp setup for optimum clinical visualization.

RESULTS

Most of the light directed into the temporal limbus in SS is lost (52%) into the sclera or reemitted back to the clinician. Only 0.006% of light that transits the central cornea undergoes TIR off the anterior cornea and more significantly 0.000125% off the posterior cornea. The optimal slit-lamp setup parameters to maximize the clinician's visualization are also summarized.

CONCLUSIONS

The propagation of light within SS primarily does not occur by TIR off the posterior cornea but rather the direct transcameral propagation of light. SS also represents an inefficient usage of light, with approximately half of the light creating a potential glare source for clinicians. We have formulated a recommended set of parameters for the slit-lamp setup to maximize clinical visualization. We also describe the transcameral pathways involved in SS that create a corneal "backlighting" effect. Almost a century after Graves original description, the optics of this phenomenon are described here.