High Resolution LCD TFT Monitor
The 22” high resolution monitor (1920 X 1080 SXGA) monitor in which the optotypes are presented, displays a flicker free, luminous intensity of slightly over 280 cd/mtr. 2 The color of its light resembles that of sunlight and has a color temperature of 4000° K. The contrast of the dark optotypes on the bright test field totals 98%. As shown in the photomacrograph from an active matrix display, each coloured pixel measures 0.264 x 0.264mm. Viewed from a distance of 4 meters, each individual pixel displays a miximum visual angle of 1/5 angular minutes.
Electronic generation and selection of the Optotypes
VariantTM uses SmartPC technology for the rapid picture setup of the optotype. The heart of the unit is an Intel CPU with a special graphics controller, required for the control of the LCD TFT screen. This combination displays a very high resolution image of even the smallest optotype which is the requirement for vision testing. The result is as shown in the fig.2.
VariantTM uses DOM/Flash card for data memory, which has many benefits over the hard disk normally used for mass storage.
The use of the LINUX platform has made the software very strudy, crash proof and allows the user to ‘Switch OFF’ the system instantaneously, without going through any ‘Shut Down’ procedure.
The optotypes are selectable by means of an ergonomically designed infrared remote control device. The VariantTM can be set up at a testing distance of either 8, 10, 12or 20ft. as desired by the user.
Astig Fan & Block
VariantTM Digital Vision Testing Chart has individual 10° Astigmatic dual meridian charts. It has 19 astigmatism tests 0° axis to 180° axis. Each astigmatism verification frame consists of one set of two multiple bars placed at 90° opposite meridians. When both the meridians appear equally clear and dark, the patient astigmatic value is perfectly corrected. Cylinder correction is much simpler now!
Contrast Sensitivity Test
The VariantTM contrast sensitivity test is designed to be part of your routine examination. Letter contrast sensitivity testing is in principle fast to administer, accurate and easy for patient populations to understand : The VariantTM uses CS charts similar to the ETDRS acuity chart, with the LOG value starting from 0.7 and decreasing by 0.1 LOG units up to -0.2. The test has 10 lines of 5 letters declining in LOG value down the chart. These are 8 different charts with contrast varying form 26% to 4% by 0.15 LOG units. The contrast charts have been calibrated between 85 and 100 cd/m2, the same as the Pelli Robson chart and that recommended by the Committee on Vision of the ‘U.S. National Academy of Sciences’ National Research Council (committee on vision, 1980).