Figure 2.

A Halometer DG (face and rear) projection 1, device base; 2, support bar; 3, feed source; 4, block unit for glare testing as seen by subject; 5, rheostat to regulate source brightness; 6, button to turn on/off the voltage feed; 7, clamp; 8, glare source window; 9, moveable optotypes (target); 10, mechanical mechanism for moving the optotypes to/from the glare source; 11, voltage feed plug; 12, a button for choosing among different optotypes, operator side; 13, electronic display of shifted optotype position, operator side; 14, metric scale of optotype distance from glare source, operator side; 15, metric distance scale of the optotype distance from glare source, operator side. B. Principle of the disability glare test, based on the measurement of the glare radius (r, mm) a new metric for glare sensitivity. I₀ = Indicatrix of light scatter; ϕ = angle. The technique utilizes a self-illuminating red or green optotype target and tangential 2 mm ‘point light source’ seen from a distance of 30 cm. The patient’s task is to move the optotype closer to the glare source until it disappears due to the veiling glare from the glare source. A halometer score is determined as follows. The illuminous (in red or green) target is approached from the source so that the patient becomes unable to distinguish the target from the source and then, the target is slowly taken away until the exact moment when the patient distinguishes the target; at this time, the incident light angle ϕ between the source and the target is measured. The target is always fixated with the foveal vision. The target and the ‘point light source’ are viewed in the same vertical plane, tangential to the plane of emitted light. In this case, to measure the angle ϕ of the incident light between the source and the target, it is necessary only to measure its projection on this vertical plane, which means to measure the distance between the source and the target. The measured glare radius is defined as a target image projection for the vector of light scatter (indicator of light scatter I = I₀cos ² ϕ) when the glare source is activated and the patient is asked to recognize the target during illumination of the eye with a glare source. C. Photograph of working prototype of the Halometer DG tester. Halometer DG instrument can provide the valuable data on the intraocular light scatter in cataracts. The instrument can be used in the pre-testing examination room of optometrist and ophthalmologists offices, at Department of Motor Vehicle licensure facilities or incorporated within automobiles, for self testing. D. Vision problems during computer use. The eyes find it difficult to focus on the pixel characters. They can focus on the plane of the computer screen, but cannot sustain that focus. The eyes focus on the screen and relax to a point behind the screen, which is called the resting point of accommodation (RPA) or dark focus. The RPA is different for every individual, but for almost everyone, it is further away than the working distance to the computer. The working distance is the distance from the computer user’s eyes to the front of the screen. Therefore the eyes are constantly relaxing to the RPA, and then straining to refocus on the screen. This constant flexing of the focusing (ciliary body) muscles is what creates fatigue, and generates burning and tired eyes. In clinical studies, it has been found that there is a significant difference in the glasses prescription required for focusing on a standard printed near card (called a Snellen card) and focusing on the image of a typical computer screen, both at a viewing distance of 20 inches. Many patients needed a different correction in each eye. E. As light passes through the cataractous lens, it is diffused or scattered. The result is blurred or defocused vision.