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Biomedical subjects

H B Dick

Publications and source records attributed to H B Dick.

68 records · Page 4Linked to original sources
PubMed1999

Objective and subjective evaluation of photic phenomena after monofocal and multifocal intraocular lens implantation.

OBJECTIVE: To objectively measure and compare halo, flicker, and glare disability in pseudophakic eyes with monofocal (MONO) and multifocal (MULTI) intraocular lenses (IOLs) with respect to the influence of corneal surface quality, astigmatism, and age. DESIGN: Prospective case series. PARTICIPANTS: This clinical trial involved 28 eyes of 28 patients after small-incision cataract surgery with a MONO silicone IOL and 28 eyes of 28 patients with zonal-progressive silicone IOL. INTERVENTION: A computer program objectively determined halo, glare, and flicker. Corneal surface quality and astigmatism were measured using computerized videokeratography. Ray-tracing analysis was performed based on the videokeratography data to calculate retinal peak distance and distortion index. A questionnaire was sent to all patients to evaluate the incidence of subjective photic phenomena. RESULTS: Mean halo size (square degrees +/- standard deviation) valued 6.1 (+/- 1.3) in the MONO group and 7.2 (+/- 2.3) in the MULTI group with no statistically significant difference between MONO and MULTI. Flicker (in % contrast to add) was -0.7 (+/- 2.9) in the MONO group and -1.0 (+/- 4.2) in the MULTI group with no statistical differences. Glare (in % contrast to add) was 5.5 (+/- 16.5) in the MONO group and 6.5 (+/- 18.0) in the MULTI group with no statistical differences. Patients in the MONO group older than 70 years of age had significantly more glare than those younger than 70 years (P = 0.017). In the MULTI group, patients with corneal shape irregularities (peak distance > 6.0 microm) or astigmatism (> 1 diopter) had statistically significant greater halos than did patients with regular corneal shape (peak distance < or = 6.0 microm) or astigmatism (< or = 1 diopter) (P < 0.005). Three of 27 MONO patients and 9 of 28 MULTI patients noticed light sensations (mainly halos) after surgery that were not present before surgery, with the majority not being bothered by these at all. CONCLUSION: In monofocal as well as in multifocal eyes, halo and glare disability occurred. Patient age, corneal surface quality, and IOL design played an important role in these photic phenomena. Because these photic phenomena may be more prevalent in night driving conditions, the authors' study suggests that night driving ability, especially in the elderly patient with pseudophakia, should be examined carefully.

Adult↗
PubMed1999

Implantation of the modified endocapsular bending ring in pediatric cataract surgery using a viscoadaptive viscoelastic agent.

Cataract surgery and intraocular lens (IOL) implantation in pediatric eyes remain controversial. Using a viscoadaptive viscoelastic agent, we implanted a modified capsular bending ring (CBR) as well as an acrylic IOL with a sharp-optic-edge design in the capsular bag. All operated eyes demonstrated a low postoperative inflammatory reaction and a clinically well-centered IOL. The band-shaped, sharp-edged CBR facilitates the creation of a sharp, discontinuous bend in the equatorial capsule, which prevents anterior and posterior capsule opacification. Combining the viscoadaptive viscoelastic agent and the CBR enhances the safety of primary and secondary posterior chamber IOL implantation in pediatric cataract surgery, reduces capsule opacification, and may facilitate IOL exchange.

Biocompatible Materials↗
PubMed1999

Implantation of a toric poly(methyl methacrylate) intraocular lens to correct high astigmatism.

A 57-year-old man experienced a decrease in visual function because of cataract formation. Corneal astigmatism was 13.4 diopters (D) because he had had a penetrating keratoplasty 27 years before. Cataract surgery was planned, and biometric data for toric intraocular lens (IOL) implantation were collected for the manufacture of a custom IOL. After phacoemulsification, a toric poly(methyl methacrylate) (PMMA) IOL of +19.0 D spherical and +12.0 D cylindrical power was implanted via a sclerocorneal tunnel incision. Three months postoperatively, corneal astigmatism was 14.3 D and best corrected visual acuity (BCVA), 20/25. Postoperative refraction (+1.5 -3.0 x 90) and BCVA remained stable for 7 months. No significant IOL rotation was observed. Implantation of a toric PMMA IOL corrected high corneal astigmatism. Toric IOL technology with high cylindrical power allows enhancement of IOL surgery.

Astigmatism↗
PubMed1998

Histological and ultrastructural study of corneal tunnel incisions using diamond and steel keratomes.

PURPOSE: To study the morphology of corneal tunnel incisions using diamond and steel keratomes. SETTING: Department of Ophthalmology, University of Giessen, Germany. METHODS: Corneal tunnel incisions were performed in six human cadaver eyes using three types of diamond keratomes and a steel keratome. The incision profile and morphology were evaluated and compared using light and scanning electron microscopy. RESULTS: The steel keratome caused more disruption of corneal stromal tissue, while the diamond keratomes produced a more regular, smoother incision. The dissecting incision resulted in a smoother surface of cut stromal tissue than the stab incision. CONCLUSIONS: The high quality of corneal tunnel incisions produced with diamond keratomes is the result of their exceptional sharpness, which may have a beneficial effect on wound healing.

Cadaver↗
PubMed1997

Effect of head position on refraction in aphakic and phakic silicone-filled eyes.

BACKGROUND: The refraction of the eye is altered significantly after the instillation of silicone oil into the vitreous cavity because of the silicone oil's high refractive index. The degree of the refractive change shows diurnal variation and depends on the patient's head position. PATIENTS AND METHODS: To analyze the degree and time course of refractive changes with respect to head position, the authors performed objective refraction in five aphakic and five phakic silicone oil-instilled eyes with attached maculae using an automatic hand-held refractometer. In each patient, 25 measurements were taken at short intervals using a hand-held autorefractometer with the patient in different positions (supine, head tilted down, and primary eye position). RESULTS: The highest shift of refraction was +5.95 +/- 2.63 diopters spherical equivalent in aphakic eyes and +2.45 +/- 0.71 diopters in the phakic eyes after the patient's position was changed from supine to head tilted down. Three minutes after the position change the refractive shift was stable in almost all eyes. Only slight changes in cylinder and the respective corresponding axis with a mean cylinder shift of 10.1 +/- 5.1 degrees were noted. CONCLUSIONS: Immediately after the head position was changed, aphakic eyes demonstrated more pronounced refractive shifts than phakic eyes. The results of this study explain patients' reports of diurnal changes in visual acuity after intraocular silicone oil instillation. Refractive changes caused by silicone oil stabilized a few minutes after a change in head position.

Aphakia, Postcataract↗
PubMedDate not supplied

Long-term endothelial cell loss following phacoemulsification through a temporal clear corneal incision.

PURPOSE: To evaluate central endothelial cell loss (ECL) following clear corneal cataract surgery using two different incision sizes and the effect of ultrasound time (UST) and power on postoperative ECL and various cell parameters. METHODS: Fifty-eight patients had phacoemulsification through temporal, two-step clear corneal tunnel incisions. In Group A (n = 28), a one-piece, plate-haptic foldable silicone intraocular lens (IOL) was implanted through a 3.5 mm sutureless incision. In Group B (n = 30), a poly(methyl methacrylate) IOL was implanted through a 5.0 mm incision with one radial suture. The central endothelial cell counts were recorded preoperatively and postoperatively at 2 to 5 days, after 6 months, and after 1 year. Color-coded, computer-assisted specular microscopy was used for special cell analysis after 1 year. RESULTS: Collective data showed an ECL of 7.9 +/- 4.1% (mean +/- standard deviation) at 2 to 5 days postoperatively, 6.7 +/- 2.9% after 6 months, and 7.3 +/- 3.3% after 1 year. A direct linear relationship was found between ECL and UST and power: ECL increased as UST and power increased. After 1 year, ECL in Group A was 4.2% with UST < or = 11/2 minutes, 6.7% with UST > 11/2 to 21/2 min, and 9.6% with UST > 21/2 to 31/2 min; in Group B it was 6.0%, 7.5%, and 11.4%, respectively. Specular microscopy showed normal, age-related cell parameters 1 year postoperatively. CONCLUSIONS: Phacoemulsification with 3.5 mm clear corneal incisions produced slightly less ECL (6.7%) than phacoemulsification with 5.0 mm incisions (7.9%). Total ECL of 7.3% at 1 year postoperatively compared favorably with ECL rates of other cataract extraction methods.

Aged↗
PubMedDate not supplied

Vacuoles in the Acrysof intraocular lens as factor of the presence of serum in aqueous humor.

OBJECTIVE: Acrysoftrade mark (Alcon) foldable lenses (IOLs) have been shown to be highly biocompatible and exhibit a low incidence of posterior capsular opacification. However, minute vacuoles or 'glistenings' have been observed in some Acrysof IOLs. The clinical relevance of vacuole formation is presently unclear. To help clarify the influence of factors present under in vivo conditions on vacuole formation, the present experimental study examines the influence of aqueous humor components on the occurrence of vacuoles in Acrysof IOLs. METHODS: A total of 12 sterile Acrysof IOLs (Alcon, MA60BM) were incubated at body temperature (37 degrees C) for 3 or 6 months in anterior-chamber aqueous humor with or without human serum. The center portion was cut from two unconditioned, unhydrated, sterile control IOLs and the 12 conditioned IOLs and examined using light microscopy for vacuole formation. A third unconditioned, hydrated control IOL was examined using light and scanning electron microscopy. MEASURES: The incidence of vacuoles was quantified by two independent investigators using light microscopy. After hydration with balanced salt solution, the surface quality of a control IOL was examined using scanning electron microscopy. RESULTS: The control IOLs exhibited no or very few vacuoles. Scanning electron microscopy revealed that the control IOLs had normal surface texture without any surface vacuoles. IOLs that had been conditioned in aqueous humor without serum exhibited no great increase in the number of vacuoles, whereas IOLs conditioned in aqueous humor with serum exhibited a greater number of vacuoles that increased over time. CONCLUSIONS: The number of vacuoles increases with incubation time in aqueous humor containing serum. The addition of serum increased the proportion of lipids and proteins in the solution, which also occurs with a breakdown in the blood-aqueous barrier. The results of the present study point to a physiological factor that may lead to vacuole formation in IOLs and may aid clinicians in identifying risk factors involved in the formation of vacuoles.

Acrylates↗
PubMedDate not supplied

Physicochemical surface properties of various intraocular lenses.

PURPOSE: It is of major interest to understand how intraocular lens (IOL) surfaces interact with aqueous humor or tissues after implantation. Important parameters to describe the physicochemical surface properties are the contact angle and critical surface tension. Therefore, we performed measurements of the contact angle and critical surface tension of several commercially available IOLs. SETTING: Department of Ophthalmology, Johannes Gutenberg University, Mainz, University Eye Hospital, Tübingen, and Max Planck Institute for Polymer Research, Mainz, Germany. METHODS: A total of 17 commercially available standard quality IOL types (6 of each) of different materials from several manufacturers were studied. Scanning electron microscopy and contact angle measurements using the sessile drop method were made. RESULTS: The sessile drop method differentiated all materials based on their surface forces. The contact angle (mean +/- SD) ranged from 56.5 +/- 3.8b 3. CONCLUSION: Contact angles differed between the IOLs depending on the IOL material with the lowest contact angle in the heparin-surface-modified IOL. The contact angle measurement method generates useful information about the material surface and its potential biomaterial interactions.

Acrylic Resins↗
PubMedDate not supplied

Correlation of blood-glucose control with oxidative metabolites in plasma and vitreous body of diabetic patients.

PURPOSE: In diabetes hyperglycemia and other mechanisms lead to the production of oxidative metabolites that can enhance the production of growth factors, leading to increased proliferative activity. Strict blood-glucose control reduces the progression of retinopathy better than standard control. This study investigated patients with diabetic retinopathy for evidence of oxidative metabolites in plasma and the vitreous body, correlating these values with blood-glucose control. METHODS: The study comprised 136 patients suffering from proliferative diabetic retinopathy. They were grouped according to their mean glycosylated hemoglobin value for the last 9-12 months. Patients with values < or = 10% (mean 8.7%; n=64) were considered strict glucose control patients, those with values > 10% (mean 12.8%; n=72) were considered standard glucose control patients. Lipid peroxides were determined in blood plasma and the vitreous body by two methods (thiobarbituric acid reactive substances and malondialdehyde-like substances). If present, retinal traction with fibrovascular proliferations (>2 disk areas) was quantified and served as an indicator of proliferative activity. RESULTS: Patients with strict blood-glucose control had significantly (p < 0.01) lower lipid peroxide values in plasma and the vitreous body than standard glucose control patients. These latter had significantly (p<0.01) higher rate of fibrovascular proliferation (50%) than strict glucose control patients (9. 7%). DISCUSSION: Strict blood-glucose control leads to reduced oxidative tissue damage both systemically and locally in the eye, and reduced proliferative activity. Oxidative metabolites can stimulate proliferation by increasing the amounts of different growth factors an cytokines such as vascular endothelial growth factor. Thus, it can be speculated that in hyperglycemia the relative increase of oxidative metabolites contributes both to damage of retinal vessels and to more pronounced proliferative activity in diabetic retinopathy.

Blood Glucose↗
PubMedDate not supplied

Lidocaine-assisted xylocaine jelly anesthesia versus one quadrant sub-Tenon infiltration for self-sealing sclerocorneal incision routine phacoemulsification.

PURPOSE: To compare the effect of xylocaine jelly and intracameral lidocaine with one quadrant instant sub-Tenon infiltration for self-sealing sclerocorneal phacoemulsification. METHODS: One hundred patients were enrolled into a prospective randomized study, receiving either a combination of topical 2% xylocaine jelly and 0.5 ml of intracameral 1% lidocaine or sub-Tenon infiltration with 2 ml of 2% xylocaine on the operating table. All patients underwent a standard divide and conquer phacoemulsification procedure through a superior sclerocorneal frown incision followed by implantation of a polymethylmethacrylate intraocular lens. Intraoperative pain was indicated by the patient by squeezing the bedside nurse's hand, who allocated it to particular stages of surgery on a chart. After surgery, patients assessed the pain experienced using a 10-unit visual analogue scale. RESULTS: Pain was indicated on 31 occasions during the operation in the sub-Tenon group (mainly the injection itself) and 67 times in the topical group. The median overall subjective pain score was 3 in the jelly group and 0 in the sub-Tenon. Five eyes (10%) had to be converted to sub-Tenon during the surgery because of intolerable pain. CONCLUSIONS: Whereas lidocaine supported xylocaine jelly anesthesia provided acceptable analgesia for 90% of patients operated, sub-Tenon anesthesia proved to deliver better intraoperative comfort in all patients receiving sclerocorneal incision cataract surgery.

Aged↗
PubMedDate not supplied

Clinical outcome and subjective quality of life after photodynamic therapy in patients with age-related macular degeneration.

PURPOSE: Whereas the efficacy of photodynamic therapy (PDT) in preventing the progression of age-related macular degeneration (ARMD) is established, its effect on quality of life is under discussion. METHODS: All patients who underwent PDT during 2000 and 2001 at the University Eye Hospital of Mainz were interviewed using a standardized 82-item questionnaire on quality of life and patient satisfaction in ophthalmologic patients. Information was assessed in terms of 82 questions; global scores ranging from 1.0 (optimum self-estimated quality of life) to 4.0 (worst) were derived. Cataract patients' scores were used to characterize the ARMD patients' subjective outcome; the latter were then related to clinical outcome parameters via logistic regressions. RESULTS: A total of 84 patients (50% female, median age 77 years) were interviewed, who underwent a median of three PDT interventions. During the period of PDT treatment, their median decrease in visual acuity was 3 lines from 0.125 to 0.063. Patients who reported a subjective increase in visual function during this period showed a median private flexibility score of 1.86; patients with the subjective impression of visual function decrease, a median score of 2.71; the median scores for mobility were 2.00 versus 3.00, for flexibility in reading 1.91 versus 3.64, for psychological stress 1.56 versus 2.25, and for communicational flexibility 1.72 versus 2.25. The difference in reading flexibility was statistically significant (p=0.001) after correction for clinical cofactors. CONCLUSIONS: The established clinical benefit of PDT treatment concerning its efficacy in ARMD progression prevention coincides with an at least slight subjective benefit in quality of life and patient satisfaction. However, the latter is associated with the patients' subjective impression of visual acuity progression rather than with clinically validated outcome after PDT treatment.

Activities of Daily Living↗
PubMedDate not supplied

Disease-specific assessment of quality of life after decompression surgery for Graves' ophthalmopathy.

PURPOSE: Graves' ophthalmopathy (GO) is an organ-specific autoimmune disease. Hydrophily of accumulated acidic mucopolysaccharides into bulbar adipose tissue leads to swelling of the eye muscles. Orbital surgical decompression is performed in severe cases of compressive optic neuropathy and severe corneal exposure or failure of steroid therapy. The study was designed to evaluate decompression surgery with respect to the clinical benefit and the patient's satisfaction by means of a disease-specific questionnaire. METHODS: The 90-item study questionnaire was distributed to 105 patients with GO who underwent orbital decompression surgery at the authors' institution. RESULTS: A total of 88% of patients stated that decompression had helped them, 80% of the interviewees would undergo decompression again, 78% were content with their eye symptoms, and 71% were satisfied with the cosmetic result of decompression. Furthermore, analysis showed a clinically relevant increase in quality of life after surgery. The correlation between the clinical endpoint proptosis at last examination and the quality of life score proved to be significant (p=0.05). CONCLUSIONS: The large majority of interviewees were satisfied with the result of the orbital decompression. These results confirmed that disfiguring proptosis is an important indication for decompression surgery.

Adult↗
PubMedDate not supplied

Scanning laser polarimetry and retinal thickness analysis before and after laser in situ keratomileusis.

PURPOSE: To evaluate changes in retinal nerve fiber layer (RNFL) thickness after laser in situ keratomileusis (LASIK) using a scanning laser polarimeter with fixed corneal compensation (GDx) and the retinal thickness analyzer (RTA). METHODS: Thirty-eight eyes of 19 healthy subjects (10 female and 9 male; mean age 37.0-/+8.8 years) underwent GDx and RTA measurements before and after LASIK. All subjects revealed mild to high myopia (mean spherical refraction: -4.0-/+2.75 D). Measurements using GDx were followed by RTA measurements after pupil dilation. All measurements were performed the day before LASIK and 1 week postoperatively. RESULTS: GDx revealed a decrease in nerve fiber layer thickness measurements after LASIK, but did not reach statistical significance (p>0.05). Using RTA, mean RNFL thickness (MRNFL) and RNFL cross sectional area decreased significantly after LASIK (p=0.03 and p=0.02, respectively). CONCLUSIONS: Scanning laser polarimetry revealed a slight decrease in RNFL thickness measurements after LASIK. MRNFL and RNFL cross section were significantly lower after LASIK using RTA. The changes might be artifacts in a small group of myopic subjects.

Adult↗