Effects Of Blur And Aniseikonia Induced By Experimental Anisometropia On Stereopsis

Purpose It is well known that anisometropia is one of the main reasons that affect children's stereoscopic vision and result in amblyopia. The blur and aniseikonia resulted from anisometropia are main factors that affect stereopsis. There are two factors: 1) Aniseikonia inducing fusion difficulty; 2) Defocus inducing fusion difficulty. However, which factor is playing a leading role is still under discussion. The mechanism that experimental anisometropia affects stereoscopic vision closely correlates with the correction of anisometropia and the treatment of anisometropia amblyopia, so it is important to study this mechanism advanced. In this experiment, we induced experimental anisometropia and analyzed the effect of blur and aniseikonia on stereopsis.Methods We developed a stereopsis test system based on computer (STBC) . It can display random-dot stereograms and local stereograms in single or double screen, and its control of test condition, such as dot size, dot color, can be regulated according to the need of experiment and clinical examination. We used red-green glasses to examine single-screen, and with synoptophore to examine double-screen. In order to evaluate the reliability of STBC, we set single and double-screen examination parameters by imitating TNO, and 65 subjects be tested by STBC and TNO.We designed an aniseikonia test system based on computer(ATBC). It draws a green cross and a red loop, which can be displayed in single-screen to examine via red-green glasses, and also can be displayed in double-screen to examine via synoptophore. Subjects can adjust the size of green cross through Pageup and Pagedown buttons, until they feel the four points of cross are contacted with the inside edge of loop exactly. The computer can record the ratio of two diagrams automatically. In order to evaluate the accuracy of ATBC, we examined aniseikonia of 32 persons by single and double-screen ATBC. According to the relationship between the size of object and the image in eyes (E object size/E image size=L object/L image), to change the distance between the object and cornea can alter the size of the image on retina. We induced 1%~16% aniseikonia through altering the position of synoptophore between two screens, examined 32 normal subjects ,and compared the results with theoretical results.There are three study phases that we analyzed the mechanism that experimental anisometropia affects stereoscopic vision. First, we induced aniseikonia by moving the synoptophore to the left, examined 32 normal subjects, recorded the size of aniseikonia and stereoacuity, and observed the anti-interference ability of the subjects to aniseikonia in difference binocular disparity and the change of subjects, stereoacuity in difference aniseikonia. Second, we put lens in front of the right eye of the subjects, the degree of lens were increased laddered by 0.50D (range +1.00~+4.00D,-1.00~-4.00D), induced simply myopia and hyperopia anisometropia. Then we examined the defocus eyes, visual acuity by using self-made visual acuity chart which can be used to examine visual acuity at the distance of 850mm, observed the effect of anisometropia to visual acuity and the relationship between visual acuity and stereoacuity. Last, we recorded the aniseikonia induced by anisometropia and observed the effect of anisometropia to stereoacuity. We also neutralized the aniseikonia indued by anisometropia through moving synoptophore, observed the blur effects on stereoacuity, and analyzed the effect of blur and aniseikonia on stereoscopic vision.Results STBC intimated TNO stereogram in single or double-screen have no significant difference with that of TNO (P<0.05). It illustrates that our stereogram have the same accuracy compared with TNO stereogram, STBC can be applied to clinical examination and experimental studies.There is no significant difference between single and double-screen ATBC. After inducing 1%~16% of the aniseikonia, there is no significant difference between double-screen ATBC and theoretical results. It illustrates that ATBC can...