Assessment of stereovision with digital testing in adults and children with normal and impaired binocularity.

New digital approaches allow stereovision to be assessed with greater precision than current clinical stereo tests. Those current tests present a relatively narrow range of stimulus disparities in coarsely quantized steps. With dichoptic treatments for amblyopia emerging, more accurate assessment of especially coarse stereopsis becomes increasingly important for verifying their aim to improve 3D vision. We used digital testing in subjects of a large age range (4-59 years), with groups having both normal (n = 34) and impaired binocular vision due to unilateral amblyopia, with or without strabismus (n = 27). Random-dot stimuli were presented on a 3D monitor with shutter glasses. The test applies adaptive procedures to measure psychometric functions and provides thresholds with associated confidence intervals. Digital thresholds for controls (range 11-160 arcsec) and stereodeficient subjects (range 43-911 arcsec) were compared to the TNO, a standard clinical test which uses similar random-dot targets presented with anaglyph glasses. Agreement between digital and TNO thresholds varied with the level of stereopsis. Stereoacuity was measurable in several subjects who failed on the TNO. With the digital test we found good repeatability for both groups, with the indication of a small learning effect for subjects with coarse stereopsis. Thus, assessment of all target groups for new tests is important, and repeated testing before therapy may avoid confusing learning and treatment effects. Our digital approach supplies a large range of accurate stereo data in children and adults; together with its associated measure of variability, it will be useful in longitudinal treatment studies.

Efficiency of electronically monitored amblyopia treatment between 5 and 16 years of age: new insight into declining susceptibility of the visual system.

The notion of a limited, early period of plasticity of the visual system has been challenged by more recent research demonstrating functional enhancement even into adulthood. In amblyopia ("lazy eye") it is still unclear to what extent the reduced effect of treatment after early childhood is due to declining plasticity or lower compliance with prescribed patching. The aim of this study was to determine the dose-response relationship and treatment efficiency from acuity gain and electronically recorded patching dose rates, and to infer from these parameters on a facet of age dependence of functional plasticity related to occlusion for amblyopia. The Occlusion Dose Monitor was used to record occlusion in 27 participants with previously untreated strabismic and/or anisometropic amblyopia aged between 5.4 and 15.8 (mean 9.2) years during 4months of conventional treatment. Group data showed improvement of acuity throughout the age span, but significantly more in patients younger than 7years despite comparable patching dosages. Treatment efficiency declined with age, with the most pronounced effects before the age of 7years. Thus, electronic recording allowed this first quantitative insight into occlusion treatment spanning the age range from within to beyond the conventional age for patching. Though demonstrating improvement in over 7year old patients, it confirmed the importance of early detection and treatment of amblyopia. Treatment efficiency is presented as a tool extending insight into age-dependent functional plasticity of the visual system, and providing a basis for comparisons of effects of patching vs. emerging alternative treatment approaches for amblyopia.

Training the adult amblyopic eye with "perceptual learning" after vision loss in the non-amblyopic eye.

We recently reported acuity development in the amblyopic eye of a 60-year-old patient after loss of vision in her non-amblyopic eye. Here, we focus on the training that we implemented, based on new insights from psychophysical procedures aiming at functional visual improvement of adults ("perceptual learning"). We alternately used the following procedures: grating acuity (Teller-Cards); contrast sensitivity (Vistech-Charts); two spatial localization tests (vertical alignment, pointing); and labyrinth patterns for a eye-hand coordination exercise. One month without intervention was followed by six months of training and two blocks of pleoptic treatment. Clinical parameters were assessed monthly. Besides acuity gain, we observed enhanced grating resolution and contrast sensitivity, decreased alignment distortions, pointing shifts, mainly after pleoptics, and more efficient labyrinth tracing. A questionnaire reflected the patient's perception of the changes. These data confirm the plasticity of the adult amblyopic system, be it spontaneous due to the loss of the non-amblyopic eye or caused by the intervention or both. Further experience is necessary to isolate the role of the intervention. Our results also underline the limitation of adult plasticity, emphasizing the importance of early diagnosis and treatment of amblyopia.

Electronic recording of occlusion treatment for amblyopia: potential of the new technology.

BACKGROUND: Approximately one third of all amblyopic eyes do not reach visual acuity of 20/40 in spite of occlusion therapy. One of the reasons is a lack of adherence to therapy, which, however, could not be quantified in the past. Experience with new devices (occlusion dose monitors, ODMs) for electronic recording of occlusion has recently been reported. The aim of the present study was to evaluate the potential of the ODMs developed in The Netherlands. Various features were tested, including the reliability of the ODM recordings compared to diaries, two ODMs used simultaneously on one patch, the influence of the ambient temperature, and the specificity of the recording pattern for measurements on the eye. METHODS: The ODMs were taped to the outside of the standard occlusion patch and measured the temperature difference between their front and back surfaces. Members of the research group and the families of two patients kept occlusion diaries while using the ODMs. Recorded and written occlusion periods were compared. Measurements were carried out under various conditions: patch with one ODM tightly on the eye or detached (allowing peeping); ODMs taped to various parts of the body; two ODMs simultaneously on one patch; variation of room temperature. RESULTS: There was good correspondence between the occlusion times recorded by the ODMs and those from the diaries, as well as between the recordings of two ODMs used simultaneously on one patch. High ambient temperatures (33 degrees C to 37 degrees C) prevented reliable ODM measurements. Measurements on other parts of the body were misclassified with probabilities between P=0.099 and P=0.325 as measurements with the patch tightly on the eye. CONCLUSIONS: In spite of some technical limitations, the ODMs provide a chance for reliable assessment of compliance and therefore objective information on dose-response function for occlusion therapy. This will lead to a more evidence-based treatment for amblyopia.

Visual improvement during psychophysical training in an adult amblyopic eye following visual loss in the contralateral eye.

BACKGROUND: Recent publications have demonstrated neural plasticity in adult amblyopes subjected to psychophysical training based on perceptual learning. The purpose of this case report is to present rarely available prospective data of visual acuity development in a strabismic amblyope undergoing psychophysical training and pleoptic treatment after loss of function of the non-amblyopic eye. METHODS: The design is a prospective, observational and interventional case report. Visual acuity was tested monthly, with constant optical correction. The 60-year-old female patient participated in a psychophysical training implemented in our laboratory, and in pleoptic treatment. RESULTS: Slow functional improvement of the amblyopic eye was observed during a period of 10 months, both in the tests used for training and in visual acuity: single optotypes increased by 4 chart lines, crowded optotypes by 2-3 lines. CONCLUSIONS: To our knowledge, this is the first report of the new approach of perceptual learning in an adult amblyope after loss of vision in the contralateral eye. Our results represent further evidence that the visual system of adult amblyopes preserves a certain degree of neural plasticity, whether spontaneous or enhanced by training. Furthermore, that plasticity in adults is limited, and early diagnosis and treatment of amblyopia must remain the primary goal.