Astigmatic axis independent spatial frequency and contrast sensitivity target and method
A set of visual targets and a method for using these targets to evaluate the spatial frequency response and contrast sensitivity of the human visual system. The invention includes four choice test, six choice test, sinusoidal bulls eye and fundamental sinusoidal letters or optotype targets. The four and six choice targets feature sinusoidal gratings oriented vertically, horizontally and at angles thereto. The sinusoidal bull's eye target features concentric circular light and dark areas with brightness varying in a radial sinusoidal fashion. The fundamental sinusoidal optotype target features an optotype, such as a letter, that is made up of strokes, each of which have a width that is equal to ½ of a single sinusoidal period.
1. A set of targets operatively configured for display on a computer monitor for testing spatial frequency and contrast sensitivity comprising:
a) a plurality of substantially sinusoidal bull's eye targets, each featuring concentric circular light and dark areas with brightness in the concentric circular light and dark areas varying in a substantially sinusoidal fashion; and
b) each of said plurality of substantially sinusoidal bull's eye targets having a unique combination of spatial frequency and contrast level.
2. A fundamental substantially sinusoidal optotype target operatively configured for display on a computer monitor for testing spatial frequency and contrast sensitivity comprising an optotype constructed entirely from a plurality of strokes, where each of said strokes features a width equal to substantially a single sinusoidal period and a length that is substantially a multiple of the width.
3. The fundamental substantially sinusoidal optotype target of claim 2 wherein the optotype is a letter.
4. The fundamental substantially sinusoidal optotype target of claim 2 wherein the optotype features a width and a length that are equal to each other and five times the stroke width.
5. A method of testing spatial frequency and contrast sensitivity comprising the steps of:
a) providing a plurality of substantially sinusoidal bull's eye targets having concentric circular light and dark areas with brightness in the concentric circular light and dark areas varying in a substantially sinusoidal fashion, the light and dark areas being substantially uniform over a circumference thereof, and each of said targets having a unique combination of spatial frequency and contrast level;
b) providing a control;
c) displaying on a computer monitor one of said substantially sinusoidal bull's eye targets to a patient;
d) asking the patient if he sees the substantially sinusoidal bull's eye target;
e) displaying the control; and
f) asking the patient if he sees the substantially sinusoidal bull's eye target.