PubMed Health⌕ Search

Biomedical subjects

T M Maida

Publications and source records attributed to T M Maida.

8 recordsLinked to original sources
PubMed1987

Pattern electroretinogram: effects of reference electrode position.

The pattern electroretinogram has assumed greater clinical and experimental significance because of its inner retinal origins. However, clinical tests may be confounded by an artifact. We tested subjects varying reference electrode position and eye stimulated while employing the Dawson-Trick-Litzkow (DTL) fiber electrode as the active electrode. The presence of a statistically significant artifactual response could not be confirmed. However, the variability of responses elicited with the outer canthus was less and the signal-to-noise ratio greater than with other reference positions.

Analysis of Variance↗
PubMed1985

Disease-specific electrophysiological findings in adult ceroid-lipofuscinosis (Kufs disease).

Two adults with mild dementia and a history of memory loss and disequilibrium were seen in the eye clinic following complaints of acuity loss in the 20/30-20/70 (Snellen) range. Results from the fundus examination of one patient were entirely normal; the other showed minimal vascular attenuation and optic atrophy. Electrophysiology was remarkable: (1) Photopic ERG b-waves were reduced, delayed, and showed pronounced oscillations. (2) EOG 'light-rise' potentials were absent or very small. (3) Binocular pattern-VER signals showed addition of the monocular signal. Scotopic ERG signals were normal. Brain biopsy and microscopy showed intercellular, autofluorescent ceroid deposits which provided a clear diagnosis of Kufs disease. Histology of model animal retinal cells show ceroid deposits in cell classes implicated by the human retinal signals. The cluster of electrophysiological results point toward early changes in the pigment epithelium and inner plexiform layer cells as a means of noninvasive diagnosis.

Adult↗
PubMed1984

Relations between the human retinal cone and ganglion cell distribution.

The distribution of human cone cells is well known and is frequently cited. The distribution of human ganglion cells is less well known and was published in a booklet which is less frequently cited in the eye literature. Selected published curves provided by these authors and Snellen acuity data were digitally encoded, transformed to linear vertical axes where necessary, scaled and compared. Comparisons were possible along the temporal hemi-meridian and provided correlations (r = 0.99 for ganglion cells versus cone cells; r = 0.99 for ganglion cells versus acuity, and r = 0.98 for cone cells versus acuity). Integration of densities along the horizontal hemi-meridian out to 50 degrees showed that approximately 50% of the cone cells are within 18 degrees of the foveola and that approximately 50% of the ganglion cells are within 13 degrees of the foveola. Appreciation of the strong interrelations between the cone-ganglion cell distributions may provide for a better understanding of the visual of inner-retinal disease. Presently it accounts for aspects of the production of pattern-elicited retinal signals which are under intense investigation in many centers.

Humans↗
PubMed1983

Retinal and cortical pattern responses: a comparison of infants and adults.

Retinal and cortical responses to pattern reversal stimulation were recorded simultaneously in three human infants of average age 3.5 months and two adults of average age 28.5 years. The relative power of retinal signals as a function of spatial frequency for both adults and infants was very similar and extrapolated to a threshold of about 30 c/deg [6/6 (20/20)] as did the relative power of the adult cortical signal. The infant cortical signal was relatively more attenuated at higher spatial frequencies and extrapolated to a threshold of 8.5 c/deg [6/22.2 (20/74)]. A greater relative maturity of retinal as compared with cortical neural function in 3.5-month-olds is inferred.

Adult↗
PubMed1982

Human pattern-evoked retinal responses are altered by optic atrophy.

Electrical signals in response to both diffuse flashes of light and phase-alternating spatial patterns were recorded from the eyes and from the occipital scalp of a subject with a traumatic unilateral (right) optic nerve section. Clinical examination disclosed a grossly normal right eye with no light perception, a Marcus Gunn pupil, and an atrophic optic disc. The left eye was normal. The electroretinogram responses on the lesioned side (OD) were normal, but there was no pattern-evoked retinal response (PERR) and no recordable visual-evoked response present. The conclusion is that the optic nerve and ganglion cells appear to be selectively responsible for the PERR potential.

Adolescent↗
PubMed1980

Metabolism of phosphatidylcholine in the frog retina.

The biosynthesis and the turnover of phosphatidylcholine were studied in the frog retina following either (a) injection into the animal of 32PO4, 33PO4, [1,3-3H]glycerol, [2-3H]glycerol, or [methyl-3H]choline, or (b) incubation of isolated retinas in solutions containing [methyl-3H]choline. 1. Examination of the pools of lipid precursors in the retina demonstrated that the choline and phosphate pools are long-lived compared to the glycerol pool, which is metabolically very active and turns over rapidly. 2. The peak in specific activity of phosphatidylcholine synthesized from labeled glycerol occurred earlier, and was higher in the microsomal fraction than in the rod outer segments, which is consistent with synthesis of phosphatidylcholine on the microsomes of the inner segment and subsequent incorporation into the rod outer segments. 3. Autoradiography of retinas incubated in vitro with tritiated choline revealed a diffuse labeling pattern in the rod outer segments. Biochemical studies following injection of labeled glycerol showed an exponential decline in specific radioactivity of phosphatidylcholine in the rod outer segments, which is consistent with a diffuse labeling of these membranes. 4. The half-life of phosphatidylcholine in the rod outer segments synthesized from labeled glycerol was found to be 18-19 days. Based on these values, calculations were made which indicated that phosphatidylcholine in the outer segments is turning over faster than integral disc membrane proteins.

Animals↗
PubMedDate not supplied

Pattern evoked retinal response (PERR) in human: effects of spatial frequency, temporal frequency, luminance and defocus.

Spatial and temporal tuning were examined for both retinal and cortical signals using low contrast sinusoidol gratings. Maximum PERR and VECP responses occurred at the 4 Hz alternation rate and at 0.68 and 2.2 cpd, respectively. A 25% low spatial frequency attenuation (LSFA) was observed for the PERR. To test the possibility that prior inability to detect LSFA of the PERR was due to the masking of a pattern contrast response by a large amplitude local luminance response, mean luminance and optical power were varied in separate experiments. Greater relative LSFA was observed with a lower mean luminance and defocus differentially affected responses elicited by high and low spatial frequency gratings. In addition greater relative LSFA was observed when power at the second harmonic rather than amplitude was the dependent measure. We conclude that LSFA may be observed. The absence of spatial tuning in previous reports is explained by the masking of pattern contrast by local lumnance responses. Detection of LSFA in the present experiments is attributed to use of stimulus conditions which minimize local luminance responses and the use of an objective response measure with a high signal-to-noise ratio, i.e., power at the second harmonic of the stimulation frequency.

Adult↗