Aniseikonia: A condition in which the ocular image of an object as seen by one eye differs in size and shape from that seen by the other.Vision Tests: A series of tests used to assess various functions of the eyes.Lenses: Pieces of glass or other transparent materials used for magnification or increased visual acuity.Epiretinal Membrane: A membrane on the vitreal surface of the retina resulting from the proliferation of one or more of three retinal elements: (1) fibrous astrocytes; (2) fibrocytes; and (3) retinal pigment epithelial cells. Localized epiretinal membranes may occur at the posterior pole of the eye without clinical signs or may cause marked loss of vision as a result of covering, distorting, or detaching the fovea centralis. Epiretinal membranes may cause vascular leakage and secondary retinal edema. In younger individuals some membranes appear to be developmental in origin and occur in otherwise normal eyes. The majority occur in association with retinal holes, ocular concussions, retinal inflammation, or after ocular surgery. (Newell, Ophthalmology: Principles and Concepts, 7th ed, p291)Ocular Physiological Phenomena: Processes and properties of the EYE as a whole or of any of its parts.Diagnosis, Computer-Assisted: Application of computer programs designed to assist the physician in solving a diagnostic problem.Vision, Binocular: The blending of separate images seen by each eye into one composite image.Lenses, Intraocular: Artificial implanted lenses.
AniseikoniaLandolt CMicromirror device: Micromirror devices are devices based on microscopically small mirrors. The mirrors are Microelectromechanical systems (MEMS), which means that their states are controlled by applying a voltage between the two electrodes around the mirror arrays.Epiretinal membraneComputer-aided diagnosis: In radiology, computer-aided detection (CADe), also called computer-aided diagnosis (CADx), are procedures in medicine that assist doctors in the interpretation of medical images. Imaging techniques in X-ray, MRI, and Ultrasound diagnostics yield a great deal of information, which the radiologist has to analyze and evaluate comprehensively in a short time.Binocular vision: Binocular vision is vision in which creatures having two eyes use them together. The word binocular comes from two Latin roots, bini for double, and oculus for eye.Intraocular lens power calculation: The aim of an accurate intraocular lens power calculation is to provide an intraocular lens (IOL) that fits the specific needs and desires of the individual patient. The development of better instrumentation for measuring the eye's axial length (AL) and the use of more precise mathematical formulas to perform the appropriate calculations have significantly improved the accuracy with which the surgeon determines the IOL power.
(1/16) Saccade amplitude disconjugacy induced by aniseikonia: role of monocular depth cues.
The conjugacy of saccades is rapidly modified if the images are made unequal for the two eyes. Disconjugacy persists even in the absence of disparity which indicates learning. Binocular visual disparity is a major cue to depth and is believed to drive the disconjugacy of saccades to aniseikonic images. The goal of the present study was to test whether monocular depth cues can also influence the disconjugacy of saccades. Three experiments were performed in which subjects were exposed for 15-20 min to a 10% image size inequality. Three different images were used: a grid that contained a single monocular depth cue strongly indicating a frontoparallel plane; a random-dot pattern that contained a less prominent monocular depth cue (absence of texture gradient) which also indicates the frontoparallel plane; and a complex image with several overlapping geometric forms that contained a variety of monocular depth cues. Saccades became disconjugate in all three experiments. The disconjugacy was larger and more persistent for the experiment using the random-dot pattern that had the least prominent monocular depth cues. The complex image which had a large variety of monocular depth cues produced the most variable and less persistent disconjugacy. We conclude that the monocular depth cues modulate the disconjugacy of saccades stimulated by the disparity of aniseikonic images. (+info)
(2/16) Disconjugate oculomotor learning caused by feeble image-size inequality: differences between secondary and tertiary positions.
In order to examine the minimum value of image-size inequality capable of inducing lasting disconjugacy of the amplitude of saccades, six normal emmetropic subjects were exposed for 16 min to 2% image size inequality. Subjects were seated at 1 m in front of a screen where a random-dot pattern was projected and made saccades of 7.5 and 15 deg along the horizontal and vertical principal meridians and to tertiary positions in the upper and lower field. During the training period, compensatory disconjugacy of the amplitude of the saccades occurred for the principal horizontal and vertical meridians; such increased disconjugacy persisted after training, suggesting learning. In contrast, for horizontal saccades to or from tertiary positions made in the upper and lower field, no consistent changes in the disconjugacy occurred, either during training or after the training condition. In an additional experiment, three subjects read sequences of words with the 2% magnifier in front of their dominant eye: in such a task, horizontal saccades to or from tertiary positions at the upper or lower field showed appropriate and lasting disconjugacy for two of the three subjects. We conclude that even a 2% image size inequality stimulates oculomotor learning, leading to persistent disconjugacy of saccades. The small disparity created by the image-size inequality is thus compensated by the oculomotor system rather than tolerated by the sensory system (e.g. by enlarging the Panum's area). (+info)
(3/16) Differences in tests of aniseikonia.
The New Aniseikonia Test (NAT), a hand-held direct-comparison test using red/green anaglyphs, has several potential advantages as a screener. We compared the validity of the NAT to that of the Space Eikonometer in three experiments: (1) aniseikonia was induced by calibrated size lenses in a double-blind study of 15 normal subjects; (2) habitual aniseikonia was measured with both instruments in four patients; and (3) eight of the normal subjects were retested with a computer-video simulation of the NAT. The NAT underestimated induced aniseikonia by a factor of 3 in the normal subjects and underestimated habitual aniseikonia in four patients. The Space Eikonometer correctly measured the magnitude of induced aniseikonia in the normal subjects. The simulation test did not show underestimation in the eight normal subjects. We could not attribute the NAT's underestimation of aniseikonia to the red/green anaglyph method, printing error, psychophysical method, or the direct-comparison test format. We speculate that the NAT induces a different sensory fusion response to aniseikonia than do the other tests, and that this altered sensory fusion response diminishes measured aniseikonia. We conclude that the NAT is not a valid measure of aniseikonia. (+info)
(4/16) Aniseikonia associated with epiretinal membranes.
AIMS: To determine whether the computerised version of the new aniseikonia test (NAT) is a valid, reliable method to measure aniseikonia and establish whether aniseikonia occurs in patients with epiretinal membranes (ERM) with preserved good visual acuity. METHODS: With a computerised version of the NAT, horizontal and vertical aniseikonia was measured in 16 individuals (mean 47 (SD 16.46) years) with no ocular history and 14 patients (mean 67.7 (14.36) years) with ERM. Test validity was evaluated by inducing aniseikonia with size lenses. Test reliability was assessed by the test-retest method. RESULTS: In normal individuals, the mean percentage (SD) aniseikonia was -0.24% (0.71) horizontal and 0% (0.59) vertical. Validity studies revealed mean (SD) 0.990 (0.005) horizontal and 0.991 (0.004) vertical correlation coefficients, 0.985 (0.111) horizontal and 0.989 (0.102) vertical slope. Repeatability coefficients were 1.04 horizontal and 0.88 vertical. Aniseikonia in patients with ERM ranged from 4% to 14%. Eight patients showed 2% or more size difference between horizontal and vertical meridians. CONCLUSIONS: The aniseikonia test used in this study can be considered a simple, fast, valid and reliable method to measure the difference in image size perceived by each eye. Aniseikonia does occur in symptomatic patients with ERM. The effect of ERM on image size is heterogeneous across the retinal area affected. (+info)
(5/16) Validity and repeatability of a new test for aniseikonia.
PURPOSE: The Aniseikonia Inspector 1.1 (AI) is a new software product to measure aniseikonia using red-green anaglyphs. The purpose of this study was to test whether the AI is a valid and reliable test. METHODS: There were two groups of sample subjects: one at risk of aniseikonia, with anisometropia greater than or equal to 1.00 D (n= 29), and a control group (n= 45). The validity was studied by comparing the measured aniseikonia with the aniseikonia simulated with size lenses. The reliability was estimated by the Bland-Altman statistical method. RESULTS: The results showed that the AI underestimated aniseikonia and that the underestimation was greater in the horizontal than in the vertical direction. The reliability was low, with biases that were clinically insignificant, but the 95% limits of agreement were around +/-2%. The behavior of the test was similar in both groups of subjects. CONCLUSIONS: The reliability of the AI is only moderate, and professionals are therefore warned to use the results of this test with caution. (+info)
(6/16) Effect of aniseikonia on fusion.
Physiological aniseikonia is the basis of stereopsis but beyond certain limits it becomes an obstacle to fusion. It is not well established as to how much aniseikonia can be tolerated by the fusional mechanism. Different tests under different testing conditions have given a wide range of variation. On the synoptophore we had observed tolerance upto 35% aniseikonia in some cases. Under more physiological conditions on a polaroid dissociation stereoprojector we observed lesser baseline fusional vergences but tolerance in about 70% of the cases upto 30% aniseikonia while 25% could tolerate even 35% aniseikonia. However we realise that these indicate the maximal potential and not the symptom free tolerable limits. (+info)
(7/16) Magnifications of single and dual element accommodative intraocular lenses: paraxial optics analysis.
(8/16) The effect of lens-induced anisometropia on accommodation and vergence during human visual development.