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Biomedical subjects

P W Dekker

Publications and source records attributed to P W Dekker.

7 recordsLinked to original sources
PubMed2000

[Ocular hemoglobinometry--physiological variations].

BACKGROUND: To explore the relationship between ocular (fundus) hemoglobin and that sampled and measured conventionally. To look for differences in hemoglobin density determined by both methods when the body hemoglobin is acutely (blood donation) or pathologically e.g. anemia altered. PATIENTS AND METHODS: Conventional (capillary and antecubital) and ocular fundus (papillary and choroidal) determinations of hemoglobin density in 14 females and 23 males, aged 25 to 30 years were compared. Application of the ocular method before and after blood donation in 21 females and 12 males, aged 20 to 68 years was performed. All these subjects were ophthalmologically and systemically healthy. Five male and 5 female anemia patients, aged 27 to 90 years, were also measured as above. RESULTS: Good correlation between fundus hemoglobin density and capillary (r = 0.81) and venous (r = 0.61) hemoglobin was observed in healthy persons. Differences in hemoglobin density according to gender were obvious at all fundus sites measured. Following blood donation, papillary hemoglobin density in males moreover increased, while that in females decreased (F = 7.53), suggesting a gender-specific difference in the ocular blood regulation, an effect also noted in the anemia patients. CONCLUSIONS: Comparison of conventional and ocular determination of hemoglobin reveals good correlation in healthy people. However, in acute or chronic blood loss the papillary hemoglobin level differs from that measured peripherally. A gender-related regulatory capacity of the ocular tissues under low-level conditions can be shown: Male persons maintain ocular hemoglobin at a normal level even when peripheral hemoglobin falls to low values, whereas female persons show a decrease in ocular hemoglobin parallel to the venous levels. Hence, under such extreme conditions,--and only in males--the ocular method yields values other than those from the conventional method, because ocular regulatory mechanisms, otherwise undetected, are exquisitely revealed.

Adult↗
PubMed1998

Measurement of intraocular pressure during laparoscopy and its relationship to central venous pressure.

UNLABELLED: STUDY OBJECTIVE. To determine the effect of different positional degrees on hemodynamics, especially central venous pressure and intraocular pressure, and a possible interrelationship, during laparoscopic surgery. SETTING. University teaching hospital (Canadian Task Force classification II-1). PATIENTS: Seven women undergoing elective gynecologic laparoscopy. INTERVENTIONS: The women were monitored for heart rate, partial pressure of oxygen, end-tidal carbon dioxide, arterial blood pressure, central venous pressure, end-tidal isoflurane concentration, and intraocular pressure in several body positions during general anesthesia. MEASUREMENTS AND MAIN RESULTS: Intraocular pressure depends on body position (r2 = 0.58) related to central venous pressure (r2 = 0.7). Heart rate and arterial blood pressure are also dependent on the body position, but to a lesser degree. CONCLUSION: Continuous monitoring of intraocular pressure may help detect alterations in central venous pressure during general anesthesia for laparoscopic surgery. Undesirable alterations caused by degree of Trendelenburg position may negatively affect patients with high cardiac or ophthalmic risk.

Adult↗
PubMed1997

Contact lens tonometry--application in humans.

PURPOSE: To establish a standard clinical procedure for measuring intraocular pressure (Po) with the contact lens tonometer (CLT), to demonstrate possibilities for analyzing ocular pulsation and performing ophthalmodynamometry. METHODS: A reliable histogram-based analyzing system for determining Po is used. First, the ocular pressure was registered with the CLT method and compared with the Goldmann applanation pressure, measured immediately beforehand. Second, ocular pulsation was studied by recording Po for 30 to 70 seconds, and the pulse amplitude was then analyzed. Third, an ophthalmodynamometry method during slit-lamp examination was tested. The central retinal artery was observed through the contact lens while the appositional force was elevated. A mark was set at the systolic and diastolic pressure while observing arterial pulsation (similar to the Korotkoff sounds). RESULTS: Compared with the Goldmann method measurements, Po obtained with the CLT method yielded a linear regression of r = 0.7 (right eye) and r = 0.68 (left eye), and was therefore highly significant (P < 0.0001, two-tailed). Analysis of the pulse amplitude showed great variability (range, 1 to 9 mm Hg; means, 2.9 mm Hg [right eye] and 3.0 mm Hg [left eye]). The dependence of the pulse amplitude on Po and age was shown with a correlation coefficient of r = 0.55 and r = 0.59, respectively. The difference between the right and left eye of the person was < 0.5 mm Hg. CONCLUSION: The CLT can be used during slit-lamp examination and permits tonometry during ophthalmoscopy, ocular pulsation assessment at different intraocular pressures, and ophthalmodynamometry.

Blood Pressure↗
PubMed1996

[Contact glass tonometer].

BACKGROUND: This paper presents a tonometer built into a contactlens, which allows to measure the eye-pressure and to perform ophthalmoscopy at the same time. Artificially induced changes of the eye-pressure and their influence on the visible fundus can now be checked simultaneously. The contactlens-tonometer (CGT) also is able to record continuously the pulse-curve, which can indicate any circulatory problem. So, the device is expected to give us additional diagnostic criteria of early glaucoma. Each ophthalmologyst in the field will be able to perform with this device a oculodynamometry in an easy way. By this it is possible to estimate the pressure-tolerance of the optic disk from glaucoma-patients. MEASUREMENTS: There have been taken some measurements on enucleated human eyes, comparing our device with a Statham-transducer in the vitreous. We found a good correlation. In a second step, we made measurements (65) on healthy volunteers, comparing the device with Perkins-Tonometry. RESULTS AND CONCLUSIONS: We found a correlation (R = 0.58). The error of the measurements was about +/- 3 mm Hg. Considering both, the deviation of the Perkins-Tonometer with which our results were compared, and the fact of a good correlation (R = 0.999) in the study with the enucleated human eyes, we found that the contact-lens-tonometer measures the intraocular pressure exactly. In future studies, we want to analyze the dynamic component of the measurements.

Contact Lenses↗
PubMed1996

Physiological influence on ocular photometry. A review.

During the development of the ocular photometer (OPM) since 1983, we have considered several physical and physiological factors that could potentially influence the measurement and its results. Attention has been given to respiratory, circulatory, and intraocular pressure provocations, and numerous publications document the influences or lack thereof. Most recently, the authors conducted a simple reproducibility study with only 1 observer and 1 subject. Measurement of the same 2 retinal sites during a 3-week period yielded no statistically significant differences, even under relatively extreme temperature conditions. Thus, changes in readings with the OPM may be considered due to variations within the eye, such as cataract. Thus, increase in lens density may be directly and correctly expressed by dual-site measurement of retinal brightness, resulting in the contrast transfer ratio.

Cataract↗
PubMedDate not supplied

Principles of contact lens tonometry.

We constructed a contact lens with an integrated pressure-sensing device. It is housed in a container with three force-sensing elements, each 120 degrees apart, enabling measurement of the appositional force, i.e., the force with which the instrument is held against the eye. In part 1 of the study, the lens' precision was tested against a manometric transducer in five eye bank eyes. The second part examined pressure as a factor dependent on the appositional force, and the third part of the study investigated the correct procedure for measuring baseline eye pressure, p0. The instrument described here allows investigation of three examination parameters: (a) the measurement of p0, the pressure independent of the appositional force; (b) the continuous measurement of the intraocular pressure (IOP); (c) the measurement of the IOP dependent on the appositional force, including artificial IOP elevation.

Cadaver↗