Pattern-Related Visual Stress, Chromaticity, and Accommodation

PURPOSE. To investigate the impact of colored overlays on the accommodative response of individuals, with and without pattern- related visual stress (PRVS), a condition in which individuals manifest symptoms of perceptual distortion and discomfort when viewing a 3-cyc/deg square-wave grating. METHODS. Under double-masked conditions, 11 individuals who reported PRVS selected an overlay with a color individually chosen to reduce perceptual distortion of text and maximize comfort (PRVS group). Two groups of control subjects individually matched for age, sex, and refractive error were recruited. Control group 1 similarly chose an overlay to maximize comfort. Control group 2 used the same overlays as the paired PRVS participant. The overlay improved reading speed by 10% (P < 0.001), but only in the PRVS group. A remote eccentric photorefractor was used to record accommodative lag while participants viewed a cross on a background. The background was uniform or contained a grating and was either gray or had a chromaticity identical with that of the chosen overlay. There were therefore four backgrounds in all. RESULTS. Overall, the accommodative lag was 0.44 D greater in the participants with PRVS. When the background had the chosen chromaticity, the accommodative lag was reduced by an average of 0.16 D (P = 0.03) in the PRVS group, but not in the symptom-free groups: in control group 2 the colored background slightly increased the accommodative lag. CONCLUSIONS. Accommodative lag was greater in individuals susceptible to pattern-related visual stress and was reduced by a colored background. © Association for Research in Vision and Ophthalmology

The visual standards for the selection and retention of astronauts

Literature search with abstracts on visual performance standards for selection and retention of astronaut

Force-length recording of eye muscles during local-anesthesia surgery in 32 strabismus patients

Abstract. Force-length recordings were made from isolated human eye muscles during strabismus surgery in local, eye-drop anesthesia in 32 adult patients. From each muscle three recordings were made: (1) while the patient looked with the other eye into the field of action of the recorded muscle, (2) looked ahead, and (3) looked out of the field of action of the recorded muscle. Non-innervated eye muscles (state 3) had an approximately exponential relation between force and length. During contraction evoked by letting the patient look ahead or into the field of action of the muscle (states I or 2), the relation between force and length was grossly linear. The approximate spring constants of horizontal rectus muscles that had not been operated on before ranged from 2 to 4 g/mm. In palsies, the degree of muscle paresis could be quantified accurately using this method and, accordingly, cases of true superior oblique palsy could be well differentiated from strabismus sursoadductorius (= upshoot in adduction) that may mimic a superior oblique palsy. In seven patients with Graves' disease of recent onset, affected muscles were found to be very stiff when the other eye looked ahead. It was expected that these stiff muscles would be able to shorten to some extent but would not be able to lengthen, due to fibrosis of the muscle. We found, however, that the affected muscles lengthened considerably when the other eye looked out of the field of action of the muscle. This implies that, in these cases of Graves' disease of recent onset, the raised muscle tension and reduced elasticity of the affected muscles and, hence, the strabismus were primarily caused by active muscle contraction, not by fibrosis

Engineering data compendium. Human perception and performance. User's guide

The concept underlying the Engineering Data Compendium was the product of a research and development program (Integrated Perceptual Information for Designers project) aimed at facilitating the application of basic research findings in human performance to the design and military crew systems. The principal objective was to develop a workable strategy for: (1) identifying and distilling information of potential value to system design from the existing research literature, and (2) presenting this technical information in a way that would aid its accessibility, interpretability, and applicability by systems designers. The present four volumes of the Engineering Data Compendium represent the first implementation of this strategy. This is the first volume, the User's Guide, containing a description of the program and instructions for its use

Optimal deep brain stimulation site and target connectivity for chronic cluster headache

OBJECTIVE: To investigate the mechanism of action of deep brain stimulation for refractory chronic cluster headache and the optimal target within the ventral tegmental area. METHODS: Seven patients with refractory chronic cluster headache underwent high spatial and angular resolution diffusion MRI preoperatively. MRI-guided and MRI-verified electrode implantation was performed unilaterally in 5 patients and bilaterally in 2. Volumes of tissue activation were generated around active lead contacts with a finite-element model. Twelve months after surgery, voxel-based morphometry was used to identify voxels associated with higher reduction in headache load. Probabilistic tractography was used to identify the brain connectivity of the activation volumes in responders, defined as patients with a reduction of ≥30% in headache load. RESULTS: There was no surgical morbidity. Average follow-up was 34 ± 14 months. Patients showed reductions of 76 ± 33% in headache load, 46 ± 41% in attack severity, 58 ± 41% in headache frequency, and 51 ± 46% in attack duration at the last follow-up. Six patients responded to treatment. Greatest reduction in headache load was associated with activation in an area cantered at 6 mm lateral, 2 mm posterior, and 1 mm inferior to the midcommissural point of the third ventricle. Average responders' activation volume lay on the trigeminohypothalamic tract, connecting the trigeminal system and other brainstem nuclei associated with nociception and pain modulation with the hypothalamus, and the prefrontal and mesial temporal areas. CONCLUSIONS: We identify the optimal stimulation site and structural connectivity of the deep brain stimulation target for cluster headache, explicating possible mechanisms of action and disease pathophysiology

Ten Minutes Vestibular Examinations but Persistent Rehabilitative Exercises

Symposium on Neurology Highlight - S16Vertigo is a common illness that patients seek consultation in ENT clinics. Patients often have a hallucination of environmental rotation while patients with dizziness often have a sense of lightheadedness. This presentation will introduce some useful but succinct clinical examinations that medical practitioners can do in about 10 minutes to make initial diagnosis whether the vertigo has a peripheral or central cause before referring the patient for more sophisticated vertigo and vestibular assessments. Some latest technologies in assessing vestibular functions are also introduced. Vestibular or dizzy rehabilitative exercise should follow if permanent vestibular paresis is found. With unilateral vestibular lesions, asymmetry of tonic vestibulospinal activity may lead to postural and gait imbalance. With symmetrical vestibular loss, the imbalance will be more pronounced and persistent. This presentation introduces some vestibular or dizziness exercises that can be practised by the patients at home. These exercises try to provoke imbalance and dizziness but at the same time try to improve the brain to compensate for any abnormalities in the vestibular system and to retrain the brain to adapt and tolerate the information from the deficit vestibular apparatus. The exercises also train the visual and somatosensory systems to compensate and assist in balancing and reduce the sense of dizziness.published_or_final_versio

Evaluation of human binocular function with an eye-tracker

En col·laboració amb la Universitat Autònoma de Barcelona (UAB), la Universitat de Barcelona (UB) i l’Institut de Ciències Fotòniques (ICFO)This study was designed to investigate if the velocity of the stimulus used during the near point of convergence (NPC) exam affected the performance of the vergence system. The effects of target’s distance and ocular dominancy were also analyzed. 14 patients with a mean ± SD age of 26.3 ± 4.6 years participated in the study. The target used to measure the NPC was moved at three different velocities (20, 35 and 50 mm/s) along a motorized rail while the eye movements of the patient were registered with an eye-tracker. The vergence error was analyzed considering the overall range of target’s distances, and the initial and final periods. The mean ± SD vergence error obtained for the total range are: 1.05º ± 0.82º (20 mm/s), 1.13º ± 0.84º (35 mm/s) and 1.24º ± 0.89º (50 mm/s). The results obtained considering the near range of distances are: 3.04º ± 1.81º (20 mm/s), 3.14º ± 1.91º (35 mm/s) and 3.36º ± 1.95º (50 mm/s). Finally, the vergence error considering the initial part of the movement are: 0.49º ± 0.15º (20 mm/s), 0.48º ± 0.13º (35 mm/s) and 0.50º ± 0.14º (50 mm/s). There are not significant differences in vergence error with the different velocities. However, the vergence error is significantly greater when more convergence is needed. Although there is no significant effect of ocular dominancy on vergence error there is a trend demonstrating that the greater the interocular difference in vergence error, the more likely the most accurate eye agreed with the dominant eye

Accommodation : clinical and theoretical investigations

Background: Accommodative insufficiency (AI) is a relatively common visual anomaly in children and young adults with an estimated prevalence of about 5%. Patients with AI usually suffer from blur, headaches and asthenopia associated with near work. The two most important treatment regimes for AI are plus lens reading additions (PLRA) and orthoptic exercises with the aim of normalising the accommodative system. The stimulus for the accommodative system is blur, which is an even-error signal, i.e., the blur gives the magnitude of the accommodation, but lacks the directional information; therefore, it is dependent on other cues to know if the accommodation needs to be increased or reduced. The main directional cues for the accommodative system are thought to be chromatic aberration (CA) and spherical aberration (SA). Recently there has been a large interest in the use of contact lenses to correct aberrations in order to create an improved image quality or create a near addition. Aims: The purpose was to evaluate the outcome of AI treatment, to investigate the effect on accommodation response when manipulating the directional cues to accommodation and to study the effect on accommodation when using a multifocal contact lens. Material and Methods: 46 children between 7-18 years of age, diagnosed with AI were dissipating in study I and II where they were treated with PLRA (+1.00 or +2.00D) or orthoptic exercise. In study III and IV, a normal group of 40 subjects were included (age 21 to 35) and 5 AI patients (age 10 to 18). They had their aberration and accommodation measured with and without accommodative cues present, and also with a multifocal contact lens which gives a near reading addition. Results: The result showed that there was no significant difference between the two treatment methods for AI patients. Further, there was a significant difference between the PLRA given, which indicates that the PLRA should not be of the higher strength. The accommodative response was not affected when the accommodative cues was eliminated or decreased. The multifocal contact lens was not able to relax the accommodation in young normal subjects and neither on AI subjects. Discussion: Results of our study and others have shown that vision therapy (PLRA and/or orthoptic exercises) can improve the time characteristic and magnitude of accommodation response with a persistent result. The PLRA of +1.00D is preferred to allow comfortable vision at near and at the same time exercise and stimulated the accommodative system rather than completely relieved. The SA and CA were showed to not be a strong directional cue for the accommodation which indicates that there are other cues more important for directional information. Since the multifocal contact lens was not able to relax the accommodation for neither of the subjects it is therefore unlikely that subjects with AI can be effectively treated with such lens. Conclusion: Based of the finding in the studies I would like to recommend that AI subjects can be treated with either +1.00D reading addition or orthoptic exercise, however, multifocal contact lenses should not be used for the treatment purpose of AI subjects