Biomedical subjects

H Bedell

Publications and source records attributed to H Bedell.

5 recordsLinked to original sources

PubMed2000

Diagnosis of glaucoma using telemedicine--the effect of compression on the evaluation of optic nerve head cup-disc ratio.

A photograph of the optic nerve head requires a lot of disk space (over 1 MByte) for storage and may require substantial bandwidth and time for transmission to a remote practitioner for a second opinion. To test whether compression degrades the image quality of the images, 302 slides were digitized at an optical resolution of 2400 pixels/inch (945 pixels/cm) and 30 bit/pixel. The images were saved both in non-compressed TIFF format and in compressed JPEG (compression ratio of 60) format. A blinded observer measured the optic nerve head cup-disc ratio for all three groups: the original slides, uncompressed TIFF and compressed JPEG images. The results showed that digital images were less accurate than slides. However, compression, even up to a ratio of 40, did not make matters worse.

Glaucoma↗

PubMed1998

Vergence facility and target type.

PURPOSE: Target suppression-cues are considered important for valid binocular accommodative facility response. However, there are no comparable recommendations concerning the effect of target type on vergence facility response. METHODS: Ten subjects ages 16 to 19 years of either sex and any race were pooled, based on the lack of any asthenopic symptoms determined by a verbal interview with the investigator. Inclusion/exclusion criteria included vision correctable to 6/6 (20/20) Snellen acuity or better in each eye, and near-normal phorias. Vergence facility response was tested over a 1-min period using 8 delta base-in (BI) and 20 delta base-out (BO) loose prisms at near (0.4 M) for 3 different vertically oriented targets: 6/9 (20/30) Snellen letters, back-illuminated anaglyphic shapes, and modified Wirt circles. RESULTS: For the group, the mean facility response was similar among the target types [Snellen letters: 9.5 cycles per minute (cpm) +/- 5.6; anaglyphic shapes: 9.0 cpm +/- 6.3; and Wirt circles: 9.4 cpm +/- 4.5]. Group response-differences were not significantly different by one-way ANOVA polynomial regression testing at the 0.05 level (F-value = 0.03, p = 0.97, df = 2). CONCLUSIONS: Whereas a binocular accommodative facility target must have additional vectographic or anaglyphic suppression-cues, vergence facility testing may incorporate a simple and available vertical row of 6/9 (20/30) Snellen letters, which provide inherent fusional suppression-cues, for a valid binocular response.

Adolescent↗

PubMed1998

Vergence facility: establishing clinical utility.

PURPOSE: Vergence facility testing attempts to assess the ability of the fusional vergence system to respond rapidly and accurately to changing vergence demands over time [defined as the number of cycles per minute (cpm) that a stimulus can be fused through, alternating base-in (BI) and base-out (BO) prisms]. Decisions to use vergence facility as a clinical test are hampered by a lack of systematically gathered normative data. METHODS: Twenty symptomatic and 20 control subjects with ages between 18 to 35 years of either sex and any race were pooled, based on vision-symptom level determined by a self-report questionnaire. Inclusion/exclusion criteria included vision correctable to 6/6 (20/20) Snellen acuity or better in each eye and normal phorias. Vergence facility response was tested over a 1-min period, using 16 combinations of BI/BO flip prisms at 4.0 and 0.4 m, based on Morgan's norms and pilot data. RESULTS: Horizontal vergence facility responses were not the same among those with and without symptoms, and not all magnitudes of BI/BO flip prisms produced the same response difference. A single flip prism, 3 delta BI/12 delta BO, was found to differentiate optimally between groups at distance and near. Repeatability of test results (with the 3 delta BI/12 delta BO prism) was poor at distance and good at near. CONCLUSIONS: In addition to providing valuable normative data, this study indicates that the vergence system nearly resets its "zero point" at any distance and sheds further light on the results of dynamic convergence and divergence stimulation on the accommodative-vergence system. From a clinical standpoint, the results improve the diagnosis of binocular vision abnormalities. The recommended near vergence facility test is easily implemented, using a commonly available flip prism (3 delta BI/12 delta BO) and having a clinical failure criterion that is easily recalled (15 cpm, sum of the BI and BO magnitudes).

Adolescent↗

PubMed1995

Short- and long-term repeatability of Visioptic Alcon EyeMap (Visioptic EH-270) corneal topographer on normal human corneas.

The purpose of this study was to examine the short-term and long-term (6 months) repeatability of the Alcon EyeMap (Visioptic EH-270)a Computerized Corneal Topographer on normal eyes. Three measurements were taken on both eyes of 39 subjects with the corneal topographer. Both eyes of seven of these subjects were measured 6 months later in order to evaluate long-term repeatability. The data showed that short-term reliability of the instrument was acceptable with a mean standard deviation (SD) < or = 0.5 D up to 3 mm (6-mm optical zone) from the center of the normal cornea. Beyond that distance, SD's of repeated measures increased systematically, making the results less useful. Long-term repeatability of the instrument over a 6-month period was acceptable clinically, although statistically significant differences were noted.

Adult↗

PubMed1987

Visual improvement in an albinotic patient with an alteration of congenital nystagmus.

Biofeedback techniques were used to alter congenital nystagmus (CN) in an albino. In response to auditory cues, the patient was able to reduce the amplitude of the nystagmus by 50% or more. In response to a combination of auditory and visual cues, the patient was able to alter the waveform of the nystagmus in such a manner that progressively larger portions of each cycle of the nystagmus were spent with the eye relatively stationary. Presumably as a consequence of this alteration in waveform, the patient's visual acuity (VA) improved from 6/35 to 6/25. The results indicate that, although VA in albinos is limited ultimately by the presence of foveal hypoplasia, other components of the typical albinotic syndrome (such as the accompanying nystagmus) can add to the acuity reduction and should, therefore, be treated.

Adult↗