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Biomedical subjects

B Petrig

Publications and source records attributed to B Petrig.

8 recordsLinked to original sources
PubMed2000

[Measurement of eye length and eye shape by optical low coherence reflectometry].

BACKGROUND: The precise and rapid measurement of eye length and eye shape are essential for investigating eye growth regulation and myopia. For this purpose, we developed an optical low coherence reflectometer and obtained preliminary measurements in volunteers. METHODS: The instrument includes a rotating glass cube to produce longitudinal scans at a velocity of 0.42 m/s and a repetition rate of approximately 13 scans/s. Heterodyne detection of light reflected from the anterior cornea and the posterior retina permits to measure axial eye length and eye shape (off-axis eye length). Each measurement consists of five consecutive scans. Reproducibility and precision were determined in one volunteer by measuring axial eye length five consecutive times, each time repositioning the eye. Eye shapes were determined in right eyes of four volunteers by measuring eye length every 3.3 degrees from 10 degrees nasally to 10 degrees temporally. RESULTS: Axial eye length measured repeatedly in one volunteer did not differ between or within the measurements (one-factor ANOVA). The average standard deviation was 11 microns. Eye shapes a) varied substantially among subjects and b) differed considerably from the corresponding shapes of spherical model eyes with identical axial eye lengths. CONCLUSION: The newly developed reflectometer permits the precise and rapid measurement of eye length and eye shape. Such measurements, especially in children, may provide important information about mechanisms of eye growth regulation and the development of myopia.

Eye↗
PubMed1998

[Diurnal axial eye growth rhythm in chicks is modified by diurnal light-dark cycle].

BACKGROUND: In chicks, the distance from the cornea to the posterior sclera (defined as axial eye length) grows in a diurnal rhythm: growth during the day is greater than during the night. The purpose of this study was to investigate whether this diurnal, axial eye growth rhythm is influenced by the diurnal light/dark illumination cycle. METHODS: One day after hatching, 18 White Leghorn chicks were reared under a 12 hour light/dark illumination cycle. After seven days, 12 chicks were switched to continuous light; the other 6 chicks remained under the 12 hour light/dark cycle and served as controls. Every 12 hours, at times corresponding to the onset of former light and dark phases over a period of 2 days, axial eye length was measured in the right eyes by laser Doppler interferometry with a precision of 20 microns. RESULTS: In group 1, axial eye growth during time intervals corresponding to former light phases (0.063 +/- 0.024 mm; mean +/- 95% confidence limit) and dark phases (0.040 +/- 0.017 mm) were not significantly different (one-factor ANOVA). In group 2, axial eye growth during light phases (0.065 +/- 0.028 mm) was significantly greater than during dark phases (0.015 +/- 0.023 mm; p = 0.015). Significantly, total axial eye growth during the two-day period was greater in group 1 (0.206 +/- 0.015 mm) than in group 2 (0.160 +/- 0.021 mm; p = 0.02; unpaired, two-tailed Student's t-test). CONCLUSION: The diurnal, axial eye growth rhythm is strongly attenuated following an acute switch from a 12 hour light/dark cycle to continuous light. Control chicks exhibit the normal rhythm. This observation demonstrates that the diurnal, axial eye growth rhythm is influenced by the light/dark illumination cycle. Whether the alteration of the rhythm and the increased axial growth during continuous light is caused by the increased amount of light alone or by increased light-induced form vision remains to be investigated.

Age Factors↗
PubMed1997

Autoregulation of human optic nerve head blood flow in response to acute changes in ocular perfusion pressure.

BACKGROUND: Studies in animals have demonstrated that optic nerve head (ONH) blood flow (F(onh)) is autoregulated, but there is a lack of evidence for such a process in humans. Therefore, we investigated the relationship between F(onh) and mean ocular perfusion pressure (PPm) in normal volunteers when PPm is decreased through elevation of the intraocular pressure (IOP). METHODS: Laser Doppler flowmetry (LDF) was used to measure relative mean velocity (Velohn), volume (Volonh) and F(onh) of blood at sites of the ONH away from visible vessels, while PPm was decreased in two ways: (1) rapidly, by IOP increments of 15 s duration, and (2) slowly, by IOP increments of 2 min duration, both by scleral suction cup in one eye of each of nine subjects. RESULTS: A rapid and large decrease of PPm of more than 100% induced a decrease of more than 80% in F(onh). With the slower decrease in PPm, F(onh) remained constant down to a PPm of approximately 22 mm Hg (IOP = 40 mm Hg) and then decreased, predominantly due to a decrease in Velohn. Immediately after removal of the suction cup, F(onh) increased transiently by 44% above baseline. CONCLUSIONS: This study demonstrates efficient blood flow autoregulation in the OHN, which is probably brought about by an increase in vascular capacitance. The magnitude of the reactive hyperaemia agrees with the compensatory decrease in ONH vascular resistance during IOP elevation. The time scale of the autoregulatory process and the dependence of the hyperaemia upon duration of IOP elevation suggest a metabolic mechanism of autoregulation.

Adult↗
PubMed1996

FPL and VEP measures of fusion, stereopsis and stereoacuity in normal infants.

Dynamic random dot fusion, stereopsis and stereoacuity were evaluated in 149 healthy, fullterm infants, using both forced-choice preferential looking (FPL) and steady-state visual evoked potential (VEP) protocols. Few infants aged 2-3 months demonstrated fusion or stereopsis in either the FPL or VEP protocol; most infants aged 5 months and older demonstrated fusion and stereopsis in both protocols. Both FLP and VEP stereoacuity approached adult-level (< 60 sec) by 6-7 months of age. Both infants and adults exhibited non-monotonic VEP amplitude vs disparity functions with a step change in phase at an intermediate disparity, consistent with separate fine and coarse disparity mechanisms.

Aging↗
PubMed1989

Variability of automated visual fields in clinically stable glaucoma patients.

The total variability of the visual field was measured in 20 patients with open-angle glaucoma who appeared to be clinically stable and well controlled on medical therapy. All patients had at least four visual fields performed on the Octopus 201 perimeter with at least 12 months follow-up since their first visual field. The four most recently performed visual fields were analyzed. Two different methods for calculating total variability were used. One was based on the variance of the threshold determinations and the other was based on the range. The average total variability per subject was 2.8 decibels (db) using the variance-based calculation and 5.1 db using the range-based calculation. Ninety-five percent of the test locations had a variability of less than 6 db by the variance-based calculation method and 13 db by the range-based calculation method. We discuss the possibility of using this type of data to develop criteria for detection of progressive visual field loss in glaucoma.

Analysis of Variance↗
PubMed1981

Development of stereopsis and cortical binocularity in human infants: electrophysiological evidence.

Dynamic random-dot stereograms and correlograms were used to elicit visually evoked brain potentials from human infants, and these potentials were compared with potentials evoked by classical checkerboard pattern reversal. The results indicate that infants begin to produce stereoscopically evoked potentials at the age of 10 to 19 weeks, several weeks after showing classical checkerboard-evoked potentials, and suggest that the onset of cortical binocularity precedes stereopsis.

Age Factors↗
PubMed1980

Large evoked potentials to dynamic random-dot correlograms and stereograms permit quick determination of stereopsis.

The combination of three technological innovations permits the fast and objective determination of stereopsis in nonverbal subjects: (i) It is shown that dynamic random-dot correlograms (RDC) are as effective as dynamic random-dot stereograms (RDS) in eliciting large evoked potentials (EP), and that the generation of RDC is simpler than that of RDS. (ii) The presentation of RDC in the form of red-green anaglyphs is insensitive to subjects' head tilt, because alternation of correlation (binocular fusion) with uncorrelation (binocular rivalry) does not depend on the direction of binocular disparity, whereas perception of depth in RDS does. (iii) Projection TV techniques, using backprojected large screens viewed from near distances, permit noncooperative subjects (e.g., human infants or monkeys) to be surrounded with the stimulus, so they cannot look away.

Animals↗