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Biomedical subjects

S G Jacobson

Publications and source records attributed to S G Jacobson.

At least 127 records · Page 7Linked to original sources
PubMed1988

The distribution and kinetics of visual pigments in the cat retina.

An imaging fundus reflectometer has been used to study the distribution and regeneration of visual pigments in the retina of the adult living cat. Measurements were made over an area of tapetal retina extending 25 degrees nasal and 40 degrees temporal to the area centralis on the horizontal meridian and 5 degrees inferior to 40 degrees superior on the vertical meridian. The measured density differences show large variations with retinal location, with values in the central retina up to 60% higher than those in the superior region. The area of high density differences forms a horizontal streak. There are two peaks of density difference values, one centered on the area centralis and the second in the nasal section of the streak. Spectral measurements indicate that the contribution of cone pigments is negligible everywhere except at the area centralis, where it is about 5%. The distribution of density differences is shown to correlate well with anatomical data if the effects of fundal stray light are taken into account and if it is assumed that the cross section of light capture by the rods is determined by the dimensions of the inner segments. The time required for essentially complete regeneration of rhodopsin depends on retinal location, varying from about 80 min in the superior retina to more than 90 min in the regions of peak densities.

Animals↗
PubMed1988

Two types of visual dysfunction in autosomal dominant retinitis pigmentosa.

Visual thresholds and rhodopsin levels were determined in nine subjects with autosomal dominant retinitis pigmentosa. The subjects fell into two groups, corresponding to two subtypes of the disease revealed by two-color, dark-adapted static perimetry. In the first of these subtypes, rod-mediated function was variably reduced and was accompanied by a corresponding reduction in cone function in the same retinal region. Dark-adapted threshold elevations varied in a way consistent with decreased quantal absorption by the rods as a result of reduced rhodopsin levels. In the second subtype, rod function was greatly reduced or absent throughout the retina, while cone function was much less severely affected. Although the levels of rhodopsin were only about half of normal, they were much too great to account for the visual threshold elevations on the basis of decreased probabilities of absorption by the visual pigment. Rhodopsin regeneration appeared to follow normal kinetics in patients from both groups. The results indicate that the examples of the two psychophysical subtypes of AD RP investigated here have very different disease manifestations.

Adult↗
PubMed1987

Cone-mediated retinal function in cats during development.

Cone electroretinograms (ERGs) were recorded in kittens from 25 to 150 days of age and in adult cats. B-wave amplitudes in kittens between 25 and 94 days of age were either within the adult range or greater than adult responses. After about 100 days, all kittens had adult-like amplitudes. Cone b-wave implicit time was markedly prolonged at the earliest ages tested and only after 80 days was the timing like that in adult cats. Amplitude and timing of 40-Hz flicker ERGs confirmed the single flash cone ERG data. Critical flicker fusion frequency was mature by 74 days of age. These findings, taken together with previous results, indicate that there are differences in the time course of development of cone- and rod-mediated retinal function in the cat.

Aging↗
PubMed1987

Rhodopsin topography and rod-mediated function in cats with the retinal degeneration of taurine deficiency.

Cats on a taurine-deficient diet were studied with imaging fundus reflectometry and full-field electroretinography. The pattern of rhodopsin loss and the natural history of the disease were determined from maps of the rhodopsin distribution in the central and nasal retina of cats with different degrees of severity of the retinopathy. Rhodopsin loss is first detectable in a focal region of the central retina. Subsequently, there are decreases in rhodopsin in the paracentral and nasal midperipheral retina. The horizontal streak of high rhodopsin levels is preferentially reduced in this retinopathy. The b-wave amplitude of the rod-dominated ERG is markedly reduced in cats with only mildly decreased levels of rhodopsin in the peripheral retina. In an affected cat with moderate rhodopsin loss in the central retina but minimal loss nasally, a light-microscopic study of the retina showed that there was disorganization and shortening of rod outer segments and loss of rod photoreceptor cells in the areas of reduced rhodopsin levels.

Animals↗
PubMed1986

Rod or cone dysfunction: uniocular presentations.

Two patients presented with unusual uniocular electroretinographic (ERG) phenomena. One patient showed the ERG characteristics of stationary night blindness in one eye only and the other patient presented with ERG evidence of uniocular cone dysfunction. In both patients, however, further electrophysiological and psychophysical studies and serial testing provided evidence for dysfunction of both receptor systems and relatively subtle involvement of the fellow eyes.

Adult↗
PubMed1986

Automated light- and dark-adapted perimetry for evaluating retinitis pigmentosa.

Visual fields and dark-adapted thresholds, essential measurements of visual function in patients with retinitis pigmentosa (RP), are usually performed manually. The authors have modified a computerized perimeter to perform automated light- and dark-adapted static perimetry across the visual field of RP patients. Results permit assessment of the level of visual disability in the light and dark and also help define subtypes of RP.

Adaptation, Physiological↗
PubMed1986

Rod mediated retinal dysfunction in cats with zinc depletion: comparison with taurine depletion.

Cats fed for 4 months with a diet with less than 7 p.p.m. zinc developed tissue zinc depletion, as judged by reduced muscle zinc content. Dark adapted electroretinogram (ERG) thresholds became elevated in zinc depleted cats. Electroretinograms and muscle zinc levels were reversed by zinc supplementation. Rod ERG to suprathreshold stimuli became reduced in b-wave amplitude in cats with zinc depletion, but suprathreshold cone ERG were unchanged. The ERG changes in zinc depleted cats were unlike those in cats fed on a taurine depleted diet.

Animals↗
PubMed1985

Dark- and light-adapted visual evoked cortical potentials in retinitis pigmentosa.

Fifty patients with all genetic types of retinitis pigmentosa (RP) were tested with the visually evoked cortical potential (VECP) by full-field flashes of blue and red light in the dark-adapted state and white light flashes in the light-adapted state. VECPs were recorded in all but one of these patients, even those with only a few degrees of central visual field remaining. In a subgroup of patients the absence of the VECP to blue light, dark-adapted, was correlated with a final dark-adapted threshold at or above cone threshold. These observations suggest that the VECP may be a useful objective method of assessment of patients with RP especially patients without detectable ERGs.

Adaptation, Physiological↗
PubMed1983

Monocular visual form deprivation in human infants.

A preferential looking technique was used to measure visual acuity in human infants under one year of age who experienced monocular visual form deprivation. Of the 14 cases reviewed, 9 infants had monocular occlusion as therapy for esotropia; 3 infants had unilateral opacities of the ocular media; and 2 infants had unilateral eyelid closure from infection or burns. Despite differences in exact mode of deprivation, the effects on visual acuity were similar. There was a reduction in visual acuity in the deprived eye and a simultaneous increase in acuity of the non-deprived eye. These effects of monocular deprivation were not permanent. Recovery occurred with reverse deprivation or by simple cessation of the deprivation.

Cataract↗
PubMed1983

Binocular visual form deprivation in human infants.

Visual acuity was measured with a preferential looking technique in infants and toddlers with binocular form deprivation. Of the 10 children in the study, there were 5 with congenital cataracts and 5 with uncorrected high refractive errors. Infants with cataract surgery before 2 months of age showed normal early development of visual acuity. A 4 to 6 month delay before treatment resulted in reduced acuity but recovery subsequently occurred. Infants with high hyperopia or astigmatism showed no acuity deficits in the first year of life when tested with optical correction. One case of early meridional amblyopia was detected in the third year of life. The deficit was not permanent and, after a period of optical correction, there was recovery of visual acuity to normal levels.

Age Factors↗
PubMed1983

Psychophysical assessment of visual acuity in infants with visual disorders.

The measurement of visual acuity is an essential part of the eye examination of adults, but is rarely attempted in infants being examined for presumed or known eye disease. We have used a preferential looking technique to test visual acuity of infants attending a hospital eye clinic. Serial measurements of acuity of infants attending a hospital eye clinic. Serial measurements of acuity in infants with certain eye diseases can provide examples of the effects of visual deprivation on the developing human visual system. Amongst 14 cases of monocular visual form deprivation in early life, there were 9 infants who had monocular occlusion as therapy for esotropia; 3 infants who had unilateral opacities of the ocular media; and 2 infants who had unilateral eyelid closure from infection or burns. Despite differences in exact mode of deprivation, the effects on visual acuity were similar. There was a reduction of visual acuity in the deprived eye and a simultaneous increase in acuity of the non-deprived eye. These effects of monocular deprivation were not permanent. Recovery occurred with reverse deprivation or by simple cessation of the deprivation. Of 10 children with binocular visual form deprivation, there were 5 who had bilateral congenital cataracts and 5 who had bilateral uncorrected high refractive errors. Infants with cataract surgery before 2 months of age showed normal early development of visual acuity. A 4-6 month delay before treatment resulted in reduced acuity, but recovery subsequently occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed1983

Visual pigment levels in retinitis pigmentosa.

A broad-field imaging fundus reflectometer was used to determine the levels of visual pigment and their relationship to rod-mediated sensitivity in 3 patients with autosomal dominantly inherited retinitis pigmentosa. In each case the loss of sensitivity could be accounted for wholly by the decreased probability of light absorption by the rod photoreceptors resulting from the decreased levels of rhodopsin they contained. In contrast, in a subject whose night blindness was due to vitamin A deficiency, the large sensitivity loss was accompanied by a relatively small reduction in the rhodopsin level.

Female↗
PubMed1982

Visual acuity of infants with ocular diseases.

We tested the visual acuities of 110 infants with ocular disorders by a preferential-looking technique that provides fast, accurate measurements for preverbal children. The results were used to confirm initial clinical evaluations and to prescribe and monitor treatment. The test was particularly helpful in assessing the effects of occlusion therapy. The child sat on a parent's lap 50 cm away from a black partition containing two circular screens. A grating was projected on one screen and a homogeneous field was projected on the other. A hidden observer watched the infant's eye and head movements to determine which screen was preferred.

Age Factors↗
PubMed1981

Development of visual acuity in infants with congenital cataracts.

The visual acuity of 4 infants with congenital cataracts was measured serially during the first year of life by a preferential looking technique. Two infants with bilateral cataracts and no measurable acuity before surgery showed rapid development of acuity to normal levels for age after surgery and optical correction. In an infant with a unilateral cataract and an infant with a cataract and persistent hyperplastic primary vitreous marked differences in monocular acuities were found after surgery. Acuities became equal in the latter case after occlusion of the normal eye, while the other infant recovered acuity with 'bi-ocular' viewing. These acuity measurements demonstrate the sensitivity of the human visual system to binocular and monouclar visual form deprivation in the first year of life.

Cataract↗
PubMed1979

Optic nerve fibre lesions in adult cats: pattern of recovery of spatial vision.

Partial deafferentation in the pre-geniculate optic pathways of the adult cat was produced by micro-injection of diphtheria toxin. In this lesion a certain proportion of fibres was damaged while neighbouring fibres remained unaffected. Behavioural methods were used to study the time course, pattern, and extent of recovery of spatial vision after such lesions. Cats were trained to discriminate square-wave gratings from blank fields. A range of grating sizes (0.13--2.61 cycles/degree) at high contrast were presented each day and when performance was consistently 100%, the lesion was placed. At 24 h post-lesion and serially thereafter grating discrimination was tested. Contrast sensitivity was also measured before and after the lesion. All cats recovered to pre-lesion performance levels. The time course of recovery was characterized by an early rapid phase followed by a longer slower phase. The early recovery was temporally coincident with dispersal of oedema at the site of the lesion, while the later slower recovery probably represented a functional reorganization at the synapse. Optic nerve fibre analyses at one year post-lesion showed reduction in fibre content ranging from 33 to 77% in different cats without shift in the fibre size histograms. The length of recovery time was directly related to the magnitude of fibre loss. The return of spatial frequency perception was hierarchical - first medium (1--4 days), then low (1--2 months) and finally high spatial frequencies (5--8 months). Possible mechanisms are discussed and it is suggested that such a pattern of psychophysical results could be accounted for by date than the X-type.

Animals↗
PubMed1979

Behavioural studies of spatial vision in cats reared with convergent squint: is amblyopia due to arrest of development?

Visual acuity and contrast sensitivity were measured behaviourally in normal adult cats and cats reared with monocular convergent squint from 3, 6, 8, 12, and 24 weeks of age. The visual acuity of the squinting eye was significantly lower than that of the non-squinting eye in cats with squint from 3, 6, and 8 weeks of age. No significant difference in acuity between eyes was found in the 12- and 24-week squinting cats and in the controls. Contrast thresholds at all spatial frequencies tested (range 0.13--2.0 c/degrees) were higher in the squinting eye than in the non-squinting eye of cats with squint from 3 and 6 weeks of age, but differences were greater at the higher spatial frequencies. In the 8-week squinting cat, contrast thresholds were increased only at higher spatial frequencies. No significant differences in contrast sensitivity were found in the cat with squint from 24 weeks of age and in the controls. The degree of disturbance of spatial vision in squinting cats was most related to the age at onset of the squint, i.e., the earlier the onset, the more profound the amblyopia. The period of susceptibility extended from about 3 to 12 weeks of age. When compared with data on the development of visual acuity in kittens, the pattern of results from the present study suggests that convergent squint can arrest the development of spatial vision.

Age Factors↗
PubMed1979

Foveal cone electroretinograms in retinitis pigmentosa and juvenile maular degeneration.

Foveal cone electroretinograms were elicited with a hand-held stimulator-ophthalmoscope from 16 patients with retinitis pigmentosa and 17 patients with juvenile macular degeneration. Among 11 patients with retinitis pigmentosa and visual acuities of 6/9 (20/30) or better, eight had foveal cone ERGs that were normal in amplitude and b-wave implicit time; all five patients tested with visual acuities of 6/12 (20/40) to 6/18 (20/60) had foveal cone ERGs that were reduced in amplitude and normal in implicit time. All patients with juvenile macular degeneration and visual acuities of 6/15 (20/50) or worse showed subnormal amplitudes with normal or delayed implicit times, or responses indistinguishable from noise. Amplitudes tended to be smaller and delays greater among patients with juvenile macular degeneration and visual acuities of 6/60 (20/200) or worse.

Adolescent↗