CorticalPerimeter

● Cortical Perimeter - by Nasanen and Raninen - is a software tool for the evaluation of contrast sensitivity of the visual field at very low cost using ordinary computer displays. Contrast sensitivity refers to the ability to see low contrasts, i.e. small differences in brightness. ● If a sufficiently large display (e.g. 27-inch viewed at a distance 20 cm) is used, a full 30-deg-field can be measured. Alternatively, the measurement can be limited to a smaller area around the fovea, e.g. the macula area. ● In addition, it is possible to evaluate the Letter Contrast Sensitivity Function (LCSF) of central vision. ● Further, by means of the Training mode, Cortical Perimeter can be used for training possible residual vision at defective visual field locations. VISUAL FIELD TESTING Fast perimetry mode: Full 30 degree field can be evaluated in just 3.5 - 4 minutes. Medium speed perimetry mode provides spatially more accurate measurement. The measurement can be done using different combinations of stimuli and tasks: Detection of static rings, Detection of flickering rings, Identification of static letters, or Identification of flickering letters. M-scaling. The stimulus size is increased towards larger eccentricities (eccentricity = sideward angular distance from the fixation point) in order to obtain a roughly equal cortical representation as well as a roughly equal sensitivity across the visual field if the field is a healthy one. Display. The program adapts to any display size. Large displays allow measurement of larger visual field areas. LETTER CONTRAST SENSITIVITY FUNCTION (LCSF) Letter contrast sensitivity function for various spatial frequencies can be measured using the same band-pass filtered letters as used in the visual field measurement. Different spatial frequencies are achieved using letters of different sizes. Spatial frequency increases with decreasing letter size. TRAINING MODE Some scientific studies suggest that the function of peripheral vision at defective areas after cortical lesion can be improved by intensive training at least in some cases. The Training mode uses methods similar to those that have been found successful in the above-mentioned studies. Vision is trained in defective visual field locations by measuring contrast sensitivity repeatedly for a number of times during weeks or months. TOOLS FOR CALIBRATING THE DISPLAY A very quick and easy way to do the calibration is the ‘Visual calibration’. The gamma value obtained in this way is reasonably close to the true value. There is also a ‘Photometer Calibration Aid’ for gamma evaluation by measuring display luminance values.