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Biomedical subjects

F Hendrikse

Publications and source records attributed to F Hendrikse.

At least 37 records · Page 2Linked to original sources
PubMed1999

Identification of intraocular lens materials using confocal Raman spectroscopy.

PURPOSE: To develop and test a noninvasive method to identify intraocular lens (IOL) materials in vitro. SETTING: Center for Biomedical Engineering and the Department of Ophthalmology, University of Texas Medical Branch, Galveston, Texas, USA. METHODS: A laser confocal Raman spectroscopy system (Conforam) was used for the noninvasive assessment of Raman spectra in the lower and the higher spectral regions (299.1 to 1833.7 cm-1 and 2633.8 to 3819.6 cm-1, respectively) of 4 IOL materials: silicone, poly(methyl methacrylate) (PMMA), acrylic, and hydrogel. RESULTS: Each lens material showed a distinctive spectrum in both the higher and the lower spectral regions. Most materials had unique peaks and a distinct profile using 1 mW of laser power and a 1 second exposure time. All materials still had a unique spectrum in both the higher and the lower region that allowed 1 material to be distinguished from the others. CONCLUSIONS: A Conforam differentiated silicone, PMMA, acrylic, and hydrogel lenses in vitro. Raman spectroscopy using the Conforam may provide a fast, safe, and reliable noninvasive method to gain information about the material of an implanted IOL and the stability of lens materials and their coatings.

Acrylates↗
PubMed1999

Continuous computer simulation analysis of the cost-effectiveness of screening and treating diabetic retinopathy.

This paper analyzes the cost-effectiveness of screening and treating diabetic retinopathy (DR) by simulating the disease progress continuously with existing data. A new computer simulation based on Monte Carlo techniques and logistic transformation follows cohorts from diabetes onset until death in five care scenarios. For younger-onset patients, ophthalmic care reduces the prevalence of blindness by 52% or greater while savings in disability facilities and production losses surpass direct costs. For older-onset patients, less favorable results appear. Financial benefits surpass costs for juvenile-onset patients. For other patients, the net costs of ophthalmic care seem lower than in other health care programs.

Blindness↗
PubMed1999

Non-invasive assessment of ocular pharmacokinetics using Confocal Raman Spectroscopy.

A Laser Scanning Confocal Raman Spectroscopy (LSCRS) system was applied for the non-invasive quantification of the transport of a drug through the rabbit cornea in vivo. Employing LSCRS, the changes in the amplitude of a drug-specific Raman signal were assessed over time in the tearfilm and corneal epithelium of the living rabbit eye (n = 6), after topical application of 25 microL Trusopt 2%. This allowed for quantification of pharmacokinetic variables. The effect of the drug on corneal hydration was also monitored. LSCRS demonstrated adequate sensitivity and reproducibility, for continuous real-time monitoring of the Trusopt concentration. Each concentration-time curve had a bi-phasic trend; the rapid initial phase (t<8 min.) corresponds to the nonproductive losses of Trusopt from the tears (k10 = 0.24+/-0.04 min(-1), and the slower later phase (t>20 min.) is the result of transfer of the drug from the corneal epithelium to the stroma (k23 = 0.0047+/-0.0004 min(-1). Drug absorption into the corneal epithelium occurred at a rate of k12 = 0.034+/-0.006 min(-1). Trusopt caused an acute dehydrating effect, with a maximum decrease in corneal hydration of approximately 15% at approximately 60 min. following application of the drug. LSCRS has the specificity, sensitivity, reproducibility and spatial resolution for employment as a potentially valuable tool for the study of ocular pharmacokinetics.

Animals↗
PubMed1999

In vivo confocal Raman spectroscopy of the human cornea.

PURPOSE: To investigate the feasibility of a confocal Raman spectroscopic technique for the noninvasive assessment of corneal hydration in vivo in two legally blind subjects. METHODS: A laser beam (632.8 nm; 15 mJ) was maintained on the cornea by using a microscope objective lens (x25 magnification, NA = 0.5, f = 10 mm) both for focusing the incident light as well as collecting the Raman backscattered light, in a 180 degrees backscatter configuration. An optical fiber, acting as the confocal pinhole for elimination of light from out-of-focus places, was coupled to a spectrometer that dispersed the collected light onto a sensitive array detector for rapid spectral data acquisition over a range from 2,890 to 3,590/cm(-1). Raman spectra were recorded from the anterior 100-150 microm of the cornea over a period before and after topical application of a mild dehydrating solution. The ratio between the amplitudes of the signals at 3,400/cm(-1) (OH-vibrational mode of water) and 2,940/cm(-1) (CH-vibrational mode of proteins) was used as a measure for corneal hydration. RESULTS: High signal-to-noise ratio (SNR = 25) Raman spectra were obtained from the human corneas by using 15 mJ of laser light energy. Qualitative changes in the hydration of the anteriormost part of the corneas could be observed as a result of the dehydrating agent. CONCLUSION: With adequate improvements in system safety, confocal Raman spectroscopy could potentially be applied clinically as a noninvasive tool for the assessment of corneal hydration in vivo.

Aged↗
PubMed1998

Asymmetrical vertical phorias indicating dissociated vertical deviation in subjects with normal binocular vision.

We measured the symmetry of phoria angles in six normal subjects. Subjects were selected on the basis of good visual acuity and stereopsis, normal binocular eye alignment and, apart from mild refraction errors, absence of ocular abnormalities. They were instructed to look at a word on a reading chart at 2 m distance. Each measurement consisted of five subsequent intervals of 5 s duration. During these five intervals viewing was binocular, with the right eye only, binocular, with the left eye only, and binocular, respectively. Each experiment consisted of twelve measurements. Eye movements were measured with scleral coils suited for measuring in horizontal, vertical and torsional directions. Five out of six subjects displayed an asymmetrical vertical phoria; one subject showed an alternating hyperphoria; four displayed a left over right vertical phoria that was largest for left eye occlusion. Only one subject showed a symmetrical vertical phoria. Both the size of the vertical phorias and the size of the asymmetries in these vertical phorias were very small: on average 0.16 +/- 0.01 and 0.17 +/- 0.01 degree, respectively. The direction of the vertical phoria asymmetries (the largest left over right was found with left eye occlusion) and the fact that asymmetries were found more often in vertical than horizontal and torsional phorias suggest that these asymmetries are related to dissociated vertical deviation. These results suggest that dissociated vertical deviation, often observed in subjects with a disruption of binocular vision early in life, reflects the enhancement of a phenomenon that is present in normal subjects as well.

Adult↗
PubMed1998

Development of a wide field height eye topographer: validation on models of the anterior eye surface.

PURPOSE: The aim of this research was to develop a corneal topographer that determines the shape of the entire anterior surface of an eye without assumptions, and with uniformly high accuracy in the center and periphery. METHODS: Based upon a double projection of two sine wave gratings and analysis of the distortion of the sine wave gratings due to the corneal-scleral shape, point-by-point measurements of surface elevation were obtained with a sample density equal to the pixel density of the CCD-detector. Using this principle, a prototype topographer, called the Maastricht Shape Topographer (MST), was developed. The accuracy and reproducibility of the instrument were evaluated using bispheric models of the anterior surface of the eye. RESULTS: The average accuracy of height measurements was +/- 0.55 micron in the 10-mm central area and +/- 22.50 microns in the periphery (14 to 19 mm). Reconstruction accuracy of the radius of curvature was +/- 0.0155 mm (+/- 0.88 D) in the center and +/- 0.0313 mm in the periphery (sclera). Average height reproducibility standard error was 0.0282 micron in the center and 2.6156 microns in the periphery. CONCLUSIONS: With the MST, unambiguous shape measurements of the entire anterior surface of the eye are possible, with accuracy up to clinically accepted standards. MST is able to measure height over a wide area of 20 mm, with a 6-mm depth of field. The tested prototype of the device can be further improved by the use of custom-made optics in order to increase signal to noise ratio in the periphery of the image. This height topographer could offer a reliable method in cases where shape is of paramount importance, e.g., in (scleral) contact lens fitting and refractive surgery.

Contact Lenses↗
PubMed1998

Noninvasive assessment of the hydration gradient across the cornea using confocal Raman spectroscopy.

PURPOSE: The feasibility of Raman spectroscopy for the noninvasive assessment of axial corneal hydration was investigated. METHODS: A scanning confocal Raman spectroscopy system, with an axial resolution of 50 microns, was used to assess noninvasively the water (OH-bond) to protein (CH-bond) ratio as a measure of the hydration in collagen-based phantom media and rabbit corneas. RESULTS: Raman spectra with high signal-to-noise ratios were obtained under in vitro and in vivo conditions within a range of corneal hydration (H = 0.0-8.3 mg water/mg dry wt). The Raman intensity ratio OH/CH showed a strong correlation with the hydration of the phantom medium (R2 > 0.99) and the rabbit corneas (R2 > 0.95). A degree of reproducibility was seen in measurements performed at a specific depth within the cornea (SD = 1.2%-2.7%). Quantitatively, the spatially resolved corneal water content, as assessed with our method, showed an increasing gradient from the anterior to the posterior region, with a difference of approximately 0.9. Significant qualitative differences in the axial hydration gradient were observed between the in vitro and in vivo situation, caused by the presence of an intact tear-film in vivo. Characterization of the axial corneal hydration using Raman spectroscopy provided a reliable estimation of total corneal hydration compared with conventional measurements using pachymetry and lyophilization. CONCLUSIONS: The proposed noninvasive confocal Raman spectroscopic technique has the potential to assess the axial corneal water gradient with a degree of sensitivity and reproducibility.

Animals↗
PubMed1996

Alagille syndrome in a family with duplication 20p11.

Alagille syndrome (arteriohepatic dysplasia, AHD) is a well defined genetic disorder with five major features: distinctive facies, cardiovascular anomalies, paucity of interlobular bile ducts (PILBD), ocular anomalies and minor skeletal malformations. Repeatedly, structural anomalies of 20p, in most cases a deletion, have been described in patients with Alagille syndrome. We report a three generation family with AHD presenting with typical facial dysmorphology, cardiac and ocular lesions but without clinical signs of liver manifestation. Two infants died from a complex cardiovascular malformation consisting of pulmonary valve atresia, hypoplasia of the pulmonary arteries and VSD. The diagnosis was not appreciated until ocular anomalies were found in the father and the distinctive facies became apparent in the daughter. Chromosome region 20p could not be interpreted precisely by high resolution banding. Using in situ hybridization a duplication 20p11.21-p11.23 was found segregating with the disorder in the family.

Alagille Syndrome↗
PubMed1995

[Future need of eye care for patients with diabetes mellitus, costs and effectiveness].

OBJECTIVE: To determine how much vision loss caused by diabetic retinopathy can be prevented in the Netherlands until 2020, and what resources will be needed to do so. DESIGN: Computer simulation study. METHODS: The population forecasts of the Dutch Central Bureau of Statistics constituted the starting points. The literature provided data on the disease progression and the effectiveness of screening and treatment. A new continuous computer simulation assessed one scenario without eye care and four scenarios with different screening frequencies. Effects were measured in sight gain, costs were based on official charges, benefits included savings on disability facilities and reductions in production losses. RESULTS: The number of diabetic patients was estimated to increase form 287,000 in 1993 to 406,000 in 2020. Compared with a setting without ophthalmic care, full compliance with official screening guidelines would reduce the prevalence of blindness in 2020 by 45% among type I patients, and by 20% among type II patients. Financial benefits would exceed costs for type I, but not for type II diabetes. While the intensity of eye care would rise, the number of eye examinations would increase approximately in the same proportion, but the number of laser treatments would increase at a much slower rate. 30% more ophthalmologists were estimated to be required in 2020. CONCLUSIONS: The sharp increase in the number of diabetic patients plus the proven effectiveness of photocoagulation will inevitably cause a major rise in the need for ophthalmic care.

Adult↗
PubMed1993

[Role of the vitreous body in diabetic retinopathy].

UNLABELLED: In recent years it has become evident that the vitreous must play a role in various aspects of diabetic retinopathy. The exact role of the vitreous is however in many aspects still ill defined. There are structural changes of the vitreous, as for instance vitreous liquefaction and posterior vitreous detachment, that are associated with the occurrence and earlier onset of diabetic retinopathy. Further there are angiogenic and angioinhibitory factors in the vitreous which influence neovascularisation by means of endothelial cell proliferation. Photocoagulation of the retina can cause structural changes (posterior vitreal detachment) and histological changes (increased hyalocytes activity) which can protect against the progression of proliferative diabetic retinopathy. The role of vitrectomy in protecting against proliferative diabetic retinopathy is generally concerned to be related to the removal of the vitreal scaffold. But vitrectomy can also induce changes in the oxygenation of the eye. If complete detachment of the posterior vitreous can be achieved it might be possible to further slow the progression of diabetic retinopathy. CONCLUSIONS: It is possible that in the future manipulation of the vitreous by means of enzymes and lasers can play a role in the treatment and prevention of diabetic retinopathy.

Diabetic Retinopathy↗
PubMed1992

[Consensus on diagnosis, screening and treatment of diabetic retinopathy].

The management and timing of the treatment of diabetic retinopathy has changed in recent years. Screening for diabetic retinopathy should preferably be performed by ophthalmologists. However, in concert with the local ophthalmologist general physicians with knowledge and experience of eye investigations can play a certain part in the screening for diabetic retinopathy. Good communication between general physician and ophthalmologist is of special interest in detecting the risk factors; systemic hypertension, poor metabolic control, pregnancy, proteinuria and rapid metabolic control of previously high blood glucose levels. For the time being fundus photography as a screening method can only be used on a limited scale and under scientific conditions. No consensus could be reached concerning the pre-treatment use of fluorescein angiography.

Diabetic Retinopathy↗
PubMed1989

Intraocular human thrombin infusion in diabetic vitrectomies.

The effectiveness of intravitreal thrombin infusion during vitrectomy was prospectively evaluated in eight diabetic patients with persistent vitreous hemorrhages and severe proliferative vitreoretinopathy. A concentration of 80 units/ml of human thrombin diluted in BSS-plus infusion fluid was used. Bleeding time ranged between 2 and 15 seconds (mean, 5 seconds). The reduction of bleeding facilitated surgery. In five of the eight cases the vitreous was clear one day postoperatively. One month postoperatively six eyes had clear media. No additional postoperative intraocular inflammation developed. These results suggest that human thrombin causes less inflammation than bovine thrombin.

Diabetic Retinopathy↗
PubMed1988

A long-term follow-up study of laser coagulation of neovascular membranes in angioid streaks.

We treated 30 eyes (24 patients) with angioid streaks and neovascular membranes using light coagulation. Of 30 eyes, 16 showed either ameliorated or unchanged visual acuity. Twelve of the remaining 14 eyes retained a visual acuity of 20/200 or better. In 11 patients, the fellow untreated eye showed central macular degeneration with loss of central vision. The follow-up period ranged from two months to 16 years (mean, 3.4 years).

Adult↗
PubMed1988

Retinal abnormalities in Alport's syndrome.

The ophthalmological findings in 13 patients with Alport's syndrome are reported. Special attention was given to the retina and retinal functions. Flecked retinopathy was present in 12 out of the 13 cases. Two cases showed tortuosity of the retinal vessels. Retinal function tests showed no significant abnormalities. This study suggests that in Alport's syndrome, retinal lesions are more common than has been reported until now.

Adolescent↗