PubMed Health⌕ Search

Biomedical subjects

P Hendrickson

Publications and source records attributed to P Hendrickson.

At least 19 recordsLinked to original sources
PubMed1992

Lateral differences indicate future glaucoma.

Since eye pairs are anatomically and pathologically asymmetrical, we attempted to determine whether the transition from ocular hypertension to glaucoma might be typified by lateral differences in either intraocular pressure (IOP), papillary excavation, or visual field. Such lateral differences were sought in a retrospective study of the medical records of 47 patients exhibiting ocular hypertension, of whom 25 remained hypertensives and 22 developed glaucoma during the period considered. Although all visual field indices in the latter group had remained within the normal range, the same side consistently yielded significantly worse results in mean sensitivity, and the absolute value for the lateral difference in these individuals was significantly higher than that found for the patients who did not develop glaucoma. Future glaucoma is manifested when the mean sensitivity remains worse in one eye.

Adult↗
PubMed1992

Protracted ruthenium treatment of recurrent pterygium.

By combining excision with 106ruthenium irradiation in 17 patients previously operated on for persistently recurrent pterygium, we have devised an effective therapy that produces virtually no side effects and further prevents events recurrence. The ruthenium applicator shell was left in place for 2-3 h, yielding a total dosage of 2000 cGy. Only 2 of 17 patients suffered even slight recurrences, and 2 more had either motility disturbance or corneal haze. Through application of the internationally accepted total dosage of 2000 cGy, but at a relatively low dose rate, which especially protects the tissue responsible for proper healing, strong support is provided for the principle of protracted irradiation in recurrent (and possibly even primary) pterygium, permitting milder treatment and fewer recurrences.

Adult↗
PubMed1992

[Autoregulation in the choroid].

The cerebral perfusion is continuously and highly sensitively dependent on arterial pCO2. Does the ocular perfusion behave in a similar manner? To answer this question, the authors measured the following parameters before and after the inhalation of 10% CO2: a) the increase of capillary pCO2, using a transcutaneous sensor, and b) the redness (pallor) of the retinal tissue, an expression of its hemoglobin content, was measured at two retinal locations with the Ocular Photometer (OPM). Initial results from young test-volunteers and patients with documented carotis stenoses show that the choroid is able to maintain constant its blood-volume even under changing loads.

Adult↗
PubMed1992

[Discrete media clouding and its effect of contrast transfer coefficients, the pattern ERG and contrast sensitivity].

As a model for our study we selected 11 pseudophacic patients with secondary cataracts who experienced good postoperative visual acuity after extracapsular cataract extraction. Besides best visual acuity and contrast sensitivity Pattern-ERG (PERG) and Contrast-Transfer-Ratio (CTR) were measured before and after YAG-Kapsulotomy was performed. Visual acuity and contrast sensitivity increased in all patients after treatment, whereas CTR increased in eight patients. PERG was measured in five patients, in two cases its amplitudes were higher, the other measurements revealed unchanged or lower amplitudes. Our model shows that in addition to the usual psychophysic tests, with CTR and PERG there are objective methods available to measure discrete opacities of the visual system.

Cataract↗
PubMed1992

[Sources of error in planimetry of the optic nerve].

No matter how "sophisticated" they may seem to have become, contemporary methods for bioplanimetry of the optic disc vary in precision; easily overlooked or neglected optical influences must, indeed, be taken into consideration; and, of greatest detriment to the meaningfulness of any and all such results is the fact that even "experts" have difficulty in uniformly and reproducibly indicating where the boundaries of the optic disc and its excavation actually lie.

Fluorescein Angiography↗
PubMed1991

["ORO" (Opportunity Recycling in Ophthalmology) Project '90: Collection of usable ophthalmologic equipment for the Dr. Bétrix Clinic for Women/Cameroon].

The developmental-assistance entreprise, "Opportunity Recycling in Ophthalmology (ORO)", recycles used but still usable equipment in Ophthalmology and material from the storage-rooms of eye clinics and private ophthalmological practices to responsible recipients in the Third World. ORO was found in 1977 and was given "Honorable Mention" from "Prix Rolex à l'esprit d'entreprise" in 1978. The current project consists of locating, reconditioning, and organizing the transport of material for the Dr. A.-F. Bétrix Clinic in Kusseri, in the most northern province/Cameroon. As always, ORO is here, too, dependent on the generosity of clinics and private ophthalmologists.

Cameroon↗
PubMed1989

Papillary circulation dynamics in glaucoma.

The ability of glaucomatous eyes to adjust to a sudden increase in intraocular pressure was investigated in nine certain glaucoma cases and in ten normal subjects. The "dynamic provoked circulatory response" (DPCR) was determined by continuously measuring the brightness of the papilla before (baseline), during, and after an abrupt artificial elevation in intraocular pressure. Following the onset of intraocular pressure elevation, the period during which the baseline brightness of the papilla persisted (latency time) was significantly (P less than 0.001) shorter in glaucomatous eyes (0.64 +/- 0.25 s) than in normal eyes (2.39 +/- 0.68 s). This led to the suggestion that the extent to which an eye can adjust to abruptly higher intraocular pressure is measurably reduced in glaucoma. That this effect can be quantified indicates a potentially useful method for detection and follow-up of glaucoma.

Aged↗
PubMed1988

[Autoregulation of the papillary vessels and their behavior as affected by halothane].

Halothane lowers the peripheral vascular resistance and blocks autoregulation in the cerebral vessels. Proceeding from the assumption that the papillary vessels behave in like manner, the authors examined increases in papillary pallor under artificial IOP elevation in anesthetized patients with and without Halothane, using the photopapillometer. This provocation test was conducted in 14 patients, first on one eye under normal (N2O/O2) anesthesia, then on the fellow eye after steady state had been attained with subsequently administered Halothane. By quantifying ocular circulatory conditions, the demonstration of the lowering of peripheral vascular resistance in the papillary vessels under Halothane was convincing; the blockage of autoregulation was less obvious. To explain these results the authors suggest that the two effects are gradual and mutually influential.

Adult↗
PubMed1988

Morphology and time-course of defined photochemical lesions in the rabbit retina.

The present study demonstrates an experimental set-up to study light injury with defined parameters including retinal irradiance levels and spectral composition of the damaging light. The time-course of acute morphological changes at constant light intensity and increasing exposure durations (from 5-30 minutes) was evaluated, the wavelength of the damaging light being 400-550 nm. Pigment epithelial lesions appeared already after 5 minutes, and rod outer segment membrane disruptions after 15-20 minutes of light exposure. Striking was the observation of disruption and vesiculation of disk membranes at the base of rod outer segments. This "clear zone" was consistently observed beginning after twenty minutes of light exposure. The comparison of morphological changes in pigmented and albinotic eyes revealed no essential differences. This result confirms the observations of other laboratories that pigment epithelial melanin neither protects against nor promotes light damage to a significant extent. Long-term changes after light exposure revealed pigment epithelial lesions and rod outer segment disruptions, followed by macrophage invasion and pigment epithelial proliferation with subsequent loss of photoreceptor cells.

Albinism↗
PubMed1986

Contrast transfer ratio in normal, cataractous, and intraocular implant lenses. A clinical photopapillometric study.

In order to clinically evaluate the optical performance of the crystalline lens as well as that of intraocular implant lenses, measurements were made of the brightness of two markedly different and easily sited landmarks on the retina (the papilla and the macula) using the photopapillometer. The contrast transfer ratio (CTR) thus generated permitted investigation of three groups of subjects: Normal persons (n = 53) with visual acuity of 1.0 (20/20) from each mature decade of life provided values indicating the age-related changes in eyes not necessarily tending toward lens opacification. Relatively constant CTR values (approximately 2:1) were observed up to 60 years, after which the ratio fell significantly to about 1.5:1 (ranging from 1.41:1 to 1.68:1, depending on the site measured on the papilla). Such a finding in subjects with normal vision was considered to demonstrate the tendency for older lenses to become yellow, which would reduce the CTR. Patients (n = 33) who were being followed clinically for developing lens opacification had their CTRs measured for correlation with their visual acuities. Here, strong correlation (P less than 0.001) was observed. Evaluation of the improvement wrought by the implantation of an intraocular lens in yet another group of patients (n = 38) revealed an increase in the CTR to a virtually normal level (1.97:1). This method provides information about the actual optical efficiency of the lens when the other ocular media are clear, supplementing other methods for evaluating lens density and clarity, and thus further facilitating critical assessment of the progress of lens opacification.

Adult↗
PubMed1986

Respiratory and circulatory influence on photopapillometry.

Respiratory and circulatory conditions that could have an influence on measurements of pallor of the papilla were evaluated with our photopapillometer in a controlled study on canines. The brightness of the papilla rim and the width of the arterioles emerging from the optic nerve head were measured in six anesthetized dogs under normal, hypertensive, and hypotensive circulatory conditions, as well as under various respiratory manipulations, and the parameters were compared for statistical correlation. Both brightness and vessel width remained constant for a wide range of arterial pressures when the rest of the experimental conditions were kept stable at naturally occurring levels. If respiration and circulation were brought to extreme levels, however, there was a statistical tendency for the brightness of the papilla to be dependent on arterial and pulmonary arterial blood pressure. The importance of these findings is discussed with regard to their influence on objective measurements of fundus brightness.

Animals↗
PubMed1986

[The papilla and visual field in glaucoma. Relation between planimetrically determined papilla and visual field changes].

From 126 patients with ocular hypertension and/or primary open-angle glaucoma, those (n = 18) who had an untreated intraocular pressure of at least 25 mm Hg or a cup/disk ratio of at least 0.8 were selected for this study. The course of the disease was followed by means of photos of the disk and visual field examinations performed with an automated perimeter. The area of the neuroretinal rim was measured planimetrically. The mean period of observation was 3.7 years, in the course of which the size of neuroretinal rim became decreased in 10 patients, merely fluctuated in 6 patients, and increased in 2 patients. No definite correlation between the course of the visual fields and that of changes in the neuroretinal rim could be demonstrated at either the first or the last examination. Nonetheless, when the visual field changes were juxtaposed to those in the neuroretinal rim, a tendency to a decrease in rim area and an increase in visual field losses was noted. However, numerous exemplary cases showed that one cannot necessarily predict visual field losses from the size of the rim and vice versa. Comparison of estimated rim areas with those determined planimetrically obviously verifies that planimetry provides more accurate results.

Aged↗
PubMed1985

[Evaluation of the effectiveness of beta blockers on the eye].

The authors report on comparative studies of two beta-blockers with regard to various parameters (intraocular pressure, perfusion pressure, and brightness of the papilla). A differential evaluation of these medications shows that measurement of the intraocular pressure alone is not sufficient to elucidate all of their characteristics fully.

Adult↗
PubMed1985

Accommodation demand and deprivation in kitten ocular development.

The effects of accommodation demand and deprivation on the development of ocular optics was investigated in four groups of kittens (total n = 29). Group 1 consisted of five normal kittens; group 2 (nine kittens) had monocular radial keratotomy to induce relative hypermetropia and more accommodation demand as well as to impart interocular refractive differences (anisometropia); group 3 (eight kittens) received daily monocular atropine; and group 4 (seven kittens) had binocular radial keratotomy combined with daily monocular atropine. Regular examination provided documentation of ocular development from the first through the sixth months of life. Subsequently, the focal lengths of the crystalline lenses were determined in vitro. An apparent tendency for kitten eye pairs to grow toward isometropia, even when anisometropia had been induced early in life, was seen in those eyes in which the accommodative mechanism had been left intact (groups 1 and 2), but without accommodation anisometropia resulted (groups 3 and 4). There was relatively more elongation of the globe (3.08 +/- 0.22%) as well as shorter than normal focal lengths of the crystalline lens (-4.91 +/- 1.62% anterior, -2.78 +/- 1.54% posterior) in the eyes of the second group, and the eye pairs regained isometropia. In those eyes of the third and fourth groups that received atropine daily, there was relatively less elongation of the globe (-3.09 +/- 0.59% and -3.22 +/- 0.67%, respectively) and shorter crystalline lens focal lengths (-3.50 +/- 1.18% and -4.62 +/- 1.07% anterior, -2.64 +/- 1.02% and -1.59 +/- 0.62% posterior, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Accommodation, Ocular↗
PubMed1978

An injection/circulation-timing switch for angiography.

An injection/circulation-timing switch was developed to simply and precisely initiate the timing unit of the fundus camera for angiographic documentation. After starting the timer, the switch, mounted on the syringe used for injection of the tracer material, subsequently provides documentation of the total elapsed time of injection. Such quantitative data can enhance the evaluation of angiographic results and contribute to their universal comparability when combined with such qualitative data as injection location and total injectate.

Fluorescein Angiography↗
PubMed1977

[Improved method of lens photograpy using retroillumination (author's transl].

Lens photography with a fundus camera using retroillumination is suited for long term follow-ups of senile cataract development. An improved method using a 9 grade colour standard is presented, which makes a comparative evaluation of the colour of the fundus reflex possible. A colour filter effect of the lens nucleus in nuclear sclerosis can thus be evaluated.

Aged↗