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PubMed2002

The scientific basis for and efficacy of optometric vision therapy in nonstrabismic accommodative and vergence disorders.

BACKGROUND: For nearly 75 years, optometric vision therapy has been an important mode of therapy for both children and adults who manifested a range of nonstrabismic accommodative and vergence disorders. METHODS: In this article, the scientific basis for, and efficacy of, optometric vision therapy in such patients will be discussed. Using bio-engineering models of the oculomotor system as the conceptual framework, emphasis will be focused on studies that used objective recording techniques to directly assess therapeutically related changes in oculomotor responsivity. RESULTS AND CONCLUSIONS: The findings clearly support the validity of optometric vision therapy. Furthermore, the results are consistent with the tenets of general motor learning.

Accommodation, Ocular↗
PubMed1997

Glucose metabolism in cat outer retina. Effects of light and hyperoxia.

PURPOSE: To determine the roles of oxidation and glycolysis with aerobic and anaerobic lactate formation in the glucose metabolism of the cat outer retina in light and darkness. METHODS: Blood was collected from a choroidal vein and from an artery, and veno-arterial differences in lactate concentration (Lac(v-a) were determined at increasing light intensities. Blood also was sampled under conditions of darkness, light, and hyperoxia and were analyzed for oxygen, glucose, and lactate concentrations with or without blood flow determinations. RESULTS: When the dark-adapted eye was subjected to increasing light intensities, there was a reduction in the Lac(v-a), indicating reduced glycolysis in the outer part of the retina as the rods saturated. In darkness, the mean lactate formation per retina was 0.409 mumol/minute, oxygen consumption was 0.198 mumol/minute, and glucose consumption 0.236 mumol/minute. In light, the corresponding figures were 0.253, 0.166, and 0.123 mumol/minute. Hyperoxia reduced lactate formation and increased oxygen consumption in light and in darkness. CONCLUSIONS: Approximately 80% of the glucose consumed by the outer retina is used primarily in aerobic lactate formation. Because it is more efficient, oxidation of glucose still accounts for most of the energy production in light and in darkness. Light reduces oxidation as well as aerobic and anaerobic lactate formation.

Adaptation, Ocular↗
PubMed1988

Accommodative adaptation induced by sustained disparity-vergence.

Pre- and post-task measures of dark focus (DF) were used to assess the response of the accommodative system to within-task disparity-vergence in 10 late-onset myopes (LOM's) and 10 emmetropes. Disparity was induced by 3 and 6 delta base-out prisms imposed during a 3 D near-vision task undertaken for 3- and 10-min periods. Accommodation was measured after the task at 1-s intervals over a 90-s period using an objective infrared optometer to determine post-task regression of DF toward pretask values. After the 3-min task both groups show a reduction in DF adaptation with increasing disparity-vergence. After the 10-min task, disparity continues to have a significant effect on accommodative adaptation in LOM's but not in emmetropes, suggesting diminished prism adaptation in LOM's. The implications of these findings are discussed with regard to both current models of accommodation-vergence interaction and the etiology of late-onset myopia.

Accommodation, Ocular↗
PubMed1993

Perceptual adaptation in the vestibulo-ocular system: EEG correlates of spatial and temporal rearrangement.

Spatial-temporal visuomotor rearrangement caused pursuit eye movements to counteract the vestibulo-ocular reflex (VOR). Vertical head nodding produced horizontal oscillations of a light spot delayed 1 or 150 msec. Adaptation resulted in apparent complementary motion of a stationary stimulus during nodding. 16 subjects adapted and tested at 150 msec. showed a 10% magnitude apparent motion. Following normal vision, while the electroencephalogram (EEG) was recorded, subjects were readapted at 150 msec. but tested at 1 msec. (to measure temporal generalization). Individual performance was correlated with EEG alpha. Adaptation correlated negatively with O(z) and Fz intensity, and positively with O(z) frequency. Temporal generalization correlated positively with O(z) intensity and negatively with O(z)-Fz phase angle. These results suggest that visuomotor adaptability is related to electrocortical activity.

Adult↗
PubMed2003

Adaptation of the vestibulo-ocular reflex, subjective tilt, and motion sickness to head movements during short-radius centrifugation.

Head movements made while the whole body is rotating at unusually high angular velocities (here with supine body position about an earth-vertical axis) result in inappropriate eye movements, sensory illusions, disorientation, and frequently motion sickness. We investigated the acquisition and retention of sensory adaptation to cross-coupled components of the vestibulo-ocular reflex (VOR) by asking eight subjects to make headturns while being rotated at 23 rpm on two consecutive days, and again a week later. The dependent measures were inappropriate vertical VOR, subjective tilt, and motion sickness in response to 90 degrees yaw out-of-plane head movements. Motion sickness was evaluated during and following exposure to rotation. Significant adaptation effects were found for the slow phase velocity of vertical nystagmus, the reported magnitude of the subjective tilt experienced during head turns, and motion-sickness scores. Retention of adaptation over a six-day rest period without rotation occurred, but was not complete for all measures. Adaptation of VOR was fully maintained while subjective tilt was only partially maintained and motion-sickness scores continued to decrease. Practical implications of these findings are discussed with particular emphasis on artificial gravity, which could be produced in weightlessness by means of a short-radius (2 m) rotator.

Adaptation, Physiological↗
PubMed1979

Visual-motor adaptation. Quantitative demonstration in patients with posterior fossa involvement.

Short-term visual-motor adaptation to magnifying spectacle lenses was studied in normal subjects and in patients with nonacute posterior fossa lesions. When normal subjects, looking through magnifying lenses, pointed open loop to targets without viewing their hands, they initially underestimated the distance (magnification effect). After a 20-minute close-loop training or adaptation exposure period during which they viewed the performance of their hands, a modified visual-motor scheme evolved, compensating for about half of the lens-induced pointing error (adaptation effect). Removal of the lenses after adaptation caused open-loop, overshooting pointing errors (adaptation after-effect). Four patients with remission of cerebellar signs showed normal visual-motor adaptive performance, evidence of ability to recalibrate gain. One patient with persisting cerebellar ataxia was unable to recalibrate gain during close-loop visual-motor training. His history of transient palatal myoclonus implicates a role for the cerebellar-olivary system in calibration of visual-motor gain.

Adaptation, Ocular↗
PubMed1981

Disruption of insect photoreceptor membrane by divalent ions: dissimilar sensitivity of light- and dark-adapted mosquito rhabdomeres.

The conditions that lead to the formation of myelin figures in rhabdomere microvilli were studied in the larval ocelli of the mosquito Aedes aegypti. These artifacts can result from the addition of divalent ions, such as Ca2+, to primary-aldehyde fixatives, but they form subsequently during postfixation with OsO4. In light-adapted ocelli, myelin figures are concentrated at the proximal ends of the microvilli along the cytoplasmic margin of the rhabdomere. The severity of the artifact is proportional to the ion concentration: scattered myelin whorls are induced by Ca2+ concentrations as low as 5 mM; they become abundant at 15 mM to 25 mM, and displace much of the rhabdomere margin at 50 mM. In contrast, even at high concentrations of Ca2+ few membrane whorls form in dark-adapted rhabdomeres, and these are mostly located at the distal ends of the microvilli. The differential response of the rhabdomere microvilli in light and darkness does not result from a direct action of light during fixation; it reflects an underlying difference between light- and dark-adapted photoreceptor membranes. We suggest that this differential sensitivity to divalent ions is associated with the shedding of membranes from the rhabdomere, a process that is enhanced by light and reduced in darkness.

Adaptation, Ocular↗
PubMed1992

The effects of light on cyclic nucleotide metabolism of isolated cone photoreceptors.

A procedure has been developed for the isolation of cone photoreceptors from the retina of the lizard Anolis carolinensis in order to study the effects of dark- and light-adaptation on the cyclic nucleotide metabolism of these visual cells. Incubation of the retina in N2 medium with hyaluronidase and DNAase allows us to obtain intact photoreceptors with good purity (85-90%), yields (greater than 2 x 10(5) cells per retina), and more than 95% of them excluding Trypan blue. cAMP levels are 20-fold higher than cGMP levels in cells from dark-adapted animals and are decreased by 35% upon exposure to light, whereas cGMP levels show no apparent change. However, both cAMP- and cGMP-phosphodiesterases, as well as adenylate and guanylate cyclase, are activated several-fold by light, but the enzymes involved in cGMP metabolism have higher Vmaxs than the cAMP related enzymes. The apparent constant levels of cGMP found in cone photoreceptors may result from our inability to detect the very fast changes that occur in these cells when they are exposed to light.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed2001

Electroretinograms remain normal in mice lacking a synapse associated protein.

Integrin-associated protein (IAP) is normally localized to the synapse rich plexiform layers of the mammalian retina. In other neuronal systems, IAP and its ligand, P84, have been implicated in synaptic function. Previously, an abnormal distribution of P84 was noted in the IAP-null retina. To examine the potential role of IAP in the function of the retinal outer plexiform layer, we recorded electroretinograms (ERGs) from IAP-null mice and wild-type littermates. Under a wide range of stimulus conditions, there was no difference between the responses of these two groups, including ERG components that reflect post-receptoral activity. These results indicate that IAP and/or P84 may not be critical for the development and maintenance of the photoreceptor-to-bipolar cell synapse.

Adaptation, Ocular↗