Comparison of refractive state and circumferential morphology of retina, choroid, and sclera in chick models of experimentally induced ametropia.

PURPOSE: Simultaneous comparisons of the circumferential morphological tissue profiles and final refractions from form-deprivation myopia (FDM), defocus-induced myopia (DIM), and defocus-induced hyperopia (DIH) models of ametropia have been made to test the hypothesis that changes in the thickness profiles of the three coats of the eye, and particularly that of the choroid, can be predicted from the degree of induced refractive error. METHODS: Hatchling chickens (n = 23) were raised for 2 weeks wearing either a monocular translucent diffuser (FDM, n = 8), monocular -10.00 D lens goggle (DIM, n = 7), monocular +10.00 D lens goggle (DIH, n = 7), or nothing (Norm, n = 1). All animals were refracted using retinoscopy and were then sacrificed, and whole eyes were processed for scanning electron microscopy. Retinal, choroidal, and cartilaginous sclera (CS) thickness measurements were made from photographic collages of the entire circumference of the globe. Of the 23 chickens, complete morphological profile data were available for both eyes of 10 animals (nine treated and one normal). The contralateral fellow eyes (FEyes) of all nine experimental chickens were used as experimental controls as paired comparisons for statistical analyses. RESULTS: Morphological profiles of control and experimental eyes revealed significant systematic regional variations in tissue thickness. This variation was related to nasal or temporal eccentricity with the nasal side generally thinner than the temporal. Retinal, choroidal, and CS tissue from FDM and DIM eyes showed very similar anatomical responses despite significantly different degrees of refractive change. DIH eyes showed significant increases in choroidal thickness but none in retinal or CS thickness. Analysis of fellow control eyes indicated that in both myopia models (FDM and DIM), significant changes in all tissues of the untreated fellow eyes occur whereas only the choroid of the fellow eye was affected in the hyperopic (DIH) model. CONCLUSIONS: The morphological similarity observed in the circumferential profiles of the retina, choroid, and cartilaginous sclera of the FDM and DIM eyes despite approximately 20 D difference in final refraction suggests that choroidal thickness is not a good predictor of final refractive error across models. Similarly, the final refractive difference of approximately 20 D between the DIM and the DIH eyes did not receive a major contribution from the final difference in choroidal thickness (with its implied effect on vitreous chamber length).

Anomalies of genetic development as predictors of oculo-visual abnormalities in velo-cardio-facial syndrome.

BACKGROUND: Subjects with velo-cardio-facial syndrome (VCFS) were assessed to determine whether the learning disabilities (LDs) characterizing the syndrome are compounded by visual function deficits, which would be predicted on the basis of the proposed embryonic derivation of the genetic anomaly. METHODS: Twelve subjects diagnosed with VCFS underwent a vision screening with emphasis on binocular function. RESULTS: Subjects exhibited deficits in accommodation (N = 5), convergence (N = 7), fusional reserves (N = 9), and stereopsis (N = 10). Three patients were strabismic at near. No patient was in the clinically normal range for all tests of binocular function. CONCLUSIONS: Individuals with VCFS have a chromosome 22 deficit thought to alter the migration of neural crest (NC) cells, which are the embryonic precursors of the autonomic innervation of the smooth muscle components of the eye and of cranial nerves III, IV, and VI. It was predicted that VCFS patients would demonstrate reduced accommodation and convergence flexibility, which would reduce visual comfort for near work. The pathological etiology of the visual anomalies suggests that if visual training is not successful, these patients should be provided with a suitable optical reading correction from an early age.

Attentional blink in global versus local attentional modes.

PURPOSE: Brain imaging studies have shown that global and local attention activate different areas of the brain, with implication for dependence of perception on attentional state. The aim of the present experiment was to investigate the duration of the attentional blink in global versus local attention. METHODS: Rapid Serial Visual Presentation (RSVP) sequences of global/local stimuli were presented to 34 adult subjects who had to identify a target red figure followed by a determination of whether a certain probe letter, 'X' (specified to be either the global or local form), was present in the subsequent string of letters. RESULTS: Attentional blinks were longer than any previously reported (1.67 s global; 2.97 s local) and were significantly different.Thus, the length of the attentional blink is dependent on the attentional state of the subject. CONCLUSION: This pattern of results is consistent with the hypothesis that global attention mechanisms receive predominantly M-pathway input.

Motion perception in global versus local attentional modes.

PURPOSE: Global and local attention are two forms of selective visual attention which activate different areas of the cortex. The purpose of this experiment was to test subjects' motion coherence thresholds under conditions of global or local attention. It was hypothesized that thresholds in global attention would be lower than in local attention. METHODS: Eleven adult subjects participated in this study. Subjects were required to identify direction of motion at variable coherence levels, while simultaneously identifying either the global or local letter. Three velocities were used for coherent motion (3, 6 and 18 degrees/s). RESULTS: The results showed that letter identification (global or local) did not significantly affect motion coherence thresholds; however, thresholds were significantly higher at 18 degrees/s than in the lower velocities. CONCLUSIONS: These results highlight the attentional limitations of visual information shown by increased motion coherence thresholds when two objects must be identified simultaneously in a brief display.

Facial muscle spasms: an Australian study.

PURPOSE: A group of patients suffering from blepharospasm, hemifacial spasm and Meige's syndrome were surveyed to determine the delay from the onset of their condition until a correct diagnosis was reached, the attitudes of practitioners towards them and their condition, the effect of their condition on their lifestyle and the effects of different types of treatment on their conditions. METHODS: Questionnaires were offered to all patients with blepharospasm, hemifacial spasm and Meige's syndrome presenting to three ophthalmologists licensed to treat patients with botulinum toxin injections over a 12 month period. RESULTS: Patients consulted an average of 4.4 practitioners before a correct diagnosis was made and many waited a number of years before obtaining satisfactory treatment. Approximately two-thirds of all practitioners consulted were unaware of their condition. Ten per cent of patients reported a family history of similar conditions. Most patients received relief from their symptoms with treatment using injections of botulinum toxin. More than 55% of patients considered themselves to have psychological problems (usually relating to stress and trauma) that they associated with the onset of their condition. CONCLUSIONS: Facial muscle dystonias are rare and patient experiences suggest that they are poorly appreciated in the medical community. From the time they first see a practitioner with symptoms of facial dystonia, patients typically wait 2 years and see four practitioners before a correct diagnosis is made. Stress may be a factor in the symptomatic onset of this condition. Many patients describe pain as part of the presenting symptomatology. Botulinum toxin seems to be effective in the management of facial spasm.

Extended contact lens wear in the developing cynomolgus monkey eye. Recovery from adverse responses.

Soft extended wear contact lenses were designed for and fitted to 12 eyes of 11 infant semiwild cynomolgus monkeys. The lenses were satisfactorily worn over observation periods of up to 465 days, the longest continuous period of lens wear being 69 days. However, some of the corneas were subject to a pattern of complications analogous to that in human contact lens wear. Nine eyes showed adverse responses, and of these, the ocular complications were severe enough in four cases to cause abandonment of lens wear. The most remarkable feature of the complications was the rapid recovery of severe reactions to near normality in less than 24 h, indicating an impressive ability of the cornea to tolerate and survive insult. Another feature was the recurrent nature of mild complications in certain monkeys despite apparent resolution from previous episodes. There appeared to be no correlation between duration of lens wear and appearance of the first or recurrent episodes of corneal infiltration and vascularization.

Corneal thickness changes following sleep and overnight contact lens wear in the primate (Macaca fascicularis).

Corneal thickness was monitored on seven cynomolgus monkeys (Macaca fascicularis) over a 76 hour period. During this time, corneal thickness measurements were also made on six monkeys after overnight wear of a hydrogel contact lens in one eye. Mean corneal thickness was 417 +/- 12 microns. An overall diurnal variation of 16 +/- 5 microns (3.8 +/- 1.2%) was found. During the first half hour after waking, corneal thickness changes ranged from -9 microns to +14 microns. After overnight contact lens wear, the cornea had swelled an average of 42 +/- 24 microns (9.1 +/- 4.8%). Following lens removal, the cornea returned to normal thickness within approximately 90 minutes. These results are similar to those found in humans and indicate that with respect to contact lens induced corneal thickness changes, the cynomolgus monkey is a suitable model for the physiological response to contact lens wear.

Astigmatism occurring in association with pediatric eye disease.

Retrospective clinical data from 496 eyes of 256 children attending a low vision clinic were analyzed to determine the relation between different classes of disease that involve visual image degradation and astigmatism. Control data comprised refractions from 79 normal vision children. Children were classified into groups according to the category of disease (14 groups) and the reported age-of-onset of their visual disability (0 to 13 years, 5 groups). The mean astigmatism for all groups of children with low vision was larger than that of the normals and in most cases the difference was significant at the 95% level. Astigmatism was highest in children with albinism, retinitis pigmentosa, and idiopathic nystagmus. Increased prevalence of astigmatism compared to normals was noted in children having their onset of low vision as late as 13 years of age. In the low vision subjects with-the-rule astigmatism occurred more frequently than oblique or against-the-rule astigmatism and oblique astigmatism more frequently than against-the-rule astigmatism.

Disease-associated visual image degradation and spherical refractive errors in children.

Retrospective clinical data from 496 eyes of 256 children attending a low vision clinic were analyzed to determine the relation between disease states which involve visual image degradation and refractive error. Refractive data from 1023 normal vision children were used as a control. The low vision children were grouped according to their disease classification and the acknowledged age-of-onset of their visual disability. It was found that there was an overall inability to emmetropize and a trend towards myopia. It was also observed that the diseases which led to myopia were associated with a peripheral or peripheral plus central impairment of vision and that those conditions in which foveal vision was primarily impaired showed a mild hypermetropic trend. Eyes in which the visual impairment was not congenital but occurred before the age of 3 years tended to develop hypermetropia. The deviation from emmetropia decreased with increasing age-of-onset of the visual impairment, as did the variation about the mean refraction. The plastic period for emmetropization is estimated to end at 8 to 9 years of age.

Effects of retinal image degradation on ocular growth in cats.

High-powered negative and positive contact lenses have been used to produce a state of continuous retinal defocus in the eyes of 11 kittens in an attempt to induce a predictable amount of axial lengthening and myopia. Another group of six kittens had one eye continuously atropinized and a third group of four animals had the lids of one eye sutured. The axial dimensions and refraction were measured using ultrasonography and retinoscopy respectively. Although the treated eyes of eight kittens tested behaviorally were shown to be amblyopic, no myopia appeared in any animal at any stage during development and only three cats showed a small axial length difference between the two eyes. These results differ from other retinal deprivation studies reported on kittens and no satisfactory explanation for this discrepancy can be offered. However, it is suggested that the lack of change may be associated with the gross anatomy of the cat's eye, and it is concluded that myopia cannot be induced reliably in kittens by retinal image degradation.

Meridional variations of corneal shape.

The corneal shape of 196 eyes was determined by photokeratoscopy and subsequent fitting of a conicoid equation to four individual corneal meridians. This conicoid was found in almost all instances to be ellipsoidal, with the asphericity not varying between meridians. The corneal radius of curvature did vary as expected between meridians. The radii of curvature of these corneal meridians also varied with the age of the subjects, resulting in reduced corneal astigmatism, while the asphericity of each meridian did not vary substantially with age.

Menstrual cycle variations of corneal topography and thickness.

Two studies were performed to investigate dimensional stability of the cornea throughout the female menstrual cycle. In the first study, changes of corneal curvature, topography, and thickness were measured for six women for one complete menstrual cycle. Steepening of horizontal and vertical curvatures occurred at the beginning of the cycle, and flattening occurred after ovulation. Corneal thickening occurred on the second day of the cycle and around the time of ovulation, then thinning and another slight thickening on day 21. In the second study, more detailed information was sought on the timing of corneal thickness changes throughout any cycle. Corneal thickness was studied for two subjects throughout three consecutive cycles. Both subjects showed a slight decrease in thickness toward the end of the menses; thickening occurred at ovulation followed by thinning. Thickening also occurred 4 days after ovulation. Consideration of changes in urine levels of estrogen and pregnanediol suggests that rises in estrogen are accompanied by increases in corneal thickness.

Diurnal variations of corneal topography and thickness.

Measurements of central and peripheral corneal thickness, corneal topography, and central corneal curvature were made for 21 subjects at hourly intervals for 12 hr of 1 day for each subject. Values for corneal radius and asphericity were obtained from keratometry and photokeratoscopy, and their stability throughout the day was evaluated. Corneal radius was observed to steepen during the day, whereas asphericity remained constant. Corneal thickness was measured by pachometry and was found to be at its thickest on first awakening. Corneal curvature and central corneal thickness were highly correlated; low correlation was found between corneal asphericity and central corneal thickness. Some subjects exhibited large fluctuations in one or all of the parameters considered.