A program for testing alterations in night vision has been successfully developed by researchers in the University of Granada's department of optics. Using Software Halo v1.0, the “halometer” can determine a subject’s ability to detect peripheral stimuli in a controlled environment. Before the test, the researchers fixed the subject’s position with a chin cup and forehead holder at an adequate distance from the monitor where the test was displayed. Consideration was given to the light's angular diameter. The test was performed under low-light conditions (after the subject was given some minutes to adapt to the darkness). This image shows a user trying the software Halo v1.0. (Image: University of Granada) The test involved showing the subject a bright light stimulus against a dark background, along with various peripheral lower-light stimuli at the center, and in random positions and at different distances. The subject's task was to press the button of a mouse every time a peripheral stimulus was detected. Once the test was over, the software made an estimation of a parameter called "visual disturbance index," which, together with the results graphic, determines the type and intensity of visual disturbance. This score index ranges from 0 to 1: The higher the index, the stronger the influence of the halo or any other visual disturbance perceived by the observer, and the lower the subject's ability to detect the peripheral stimuli from the main disturbance. One of the advantages of the halometer developed at the University of Granada is that it can configure various test parameters: • Special parameters: The radius of the central stimulus and the peripheral stimuli can be modified. Furthermore, the number of semi-major axes where the peripheral stimuli will be displayed can be fixed, as well as the maximum distance between the stimuli and the number of stimuli per semi-major axis. • Temporary Parameters: The software allows exposure time to be adapted to the available light. • The software also can set the color and brightness of central and peripheral stimuli, and the weight and number of times each peripheral stimulus is shown. This test has been tried on various categories of eye patients, including those with cataracts, refractory eye surgery patients, those with age-related macular degeneration or unilateral keratitis, along with control groups. The results showed that, in the case of patients with keratitis, the visual disturbance index for the healthy eye is lower than that for the unhealthy eye, and the index was even lower under binocular vision conditions. However, visual disturbance indexes proved to be higher in the case of patients who had had cataracts removed, showing a higher influence of halos and, therefore, lower detection capacity. The Software Halo v1.0 was recently released by the Free-Software Bureau of the University of Granada, so it has become a scientific freeware application. This software was developed by a group coordinated by Rosario González Anera, with technical support from Seven Solutions of Granada and an ophthalmological clinic in Madrid. The research group included José Juan Castro, Carolina Ortiz and Aixa Alarcón, and it received funding from Andalusia. For more information, visit: www.ugr.es