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Biomedical subjects

D D Koch

Publications and source records attributed to D D Koch.

At least 19 recordsLinked to original sources
PubMed1999

Comparative corneal topography and refractive variables in monozygotic and dizygotic twins.

PURPOSE: To investigate the role of heredity in determining corneal shape, axial length, and overall refractive error. METHODS: Twenty monozygotic and 19 dizygotic twin pairs, age 12 to 73 years, were enrolled in the study. Zygosity was determined by physical similarity and by responses to questions adapted from surveys. Two twin pairs were excluded because of undetermined zygosity and one pair because of keratoconus (both siblings). Refractive error was determined by an automated refractor. Manifest refraction was also recorded, as well as cycloplegic refraction in subjects under age 18 years. Corneal topography data and manual keratometer readings were also obtained. Axial lengths were determined by A-scan ultrasound. Data were analyzed by Student t tests only in the right eye. Left-eye data were comparable for all variables. RESULTS: Mean intrapair difference in refractive error (spherical equivalent) was less for monozygotic than for dizygotic twins (RE: 0.41 vs 1.53; P = .001). Mean intrapair difference in axial length was less for monozygotic twins (RE: 0.39 vs 0.76 mm; P = .031). Corneal topography data (power and meridian) in all zones (3, 5, and 7 mm) also showed smaller mean differences among monozygotic pairs than dizygotic, but the difference was statistically significant only for the 5-mm zone. In addition, most Holladay Diagnostic Summary variables that were studied did not show any statistically significant differences. CONCLUSIONS: Axial length and overall refractive error have a significant genetic basis. Corneal topography data appear to have other overriding determining factors for several of the variables studied.

Adolescent↗
PubMed1999

Stability of vision during space flight in an astronaut with bilateral intraocular lenses.

PURPOSE: To report excellent and stable vision in an astronaut during space flight after bilateral cataract surgery with intraocular lenses. METHODS: A 60-year-old physician mission specialist astronaut developed cataracts and underwent phacoemulsification with insertion of one-piece polymethylmethacrylate intraocular lenses that had 6-mm optics bilaterally. Several months later, he flew on a space shuttle mission. Ocular examinations were performed before and after the mission, and the patient was questioned about visual changes during flight. RESULTS: Ocular examinations demonstrated stable bilateral posterior chamber intraocular lenses. Our subject reported excellent vision during liftoff, 18 days of microgravity, changes in cabin pressure, and reentry. CONCLUSION: Results suggest that intraocular lenses are safe, effective, and well tolerated during space flight.

Astronauts↗
PubMed1999

Evaluation of relationships among refractive and topographic parameters.

PURPOSE: To examine the relationships among several refractive and topographic parameters. SETTING: Cullen Eye Institute Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, USA. METHODS: Using computerized videokeratography (EyeSys Corneal Analysis System), 287 corneas of 150 patients were retrospectively analyzed. The Holladay Diagnostic Summary (HDS) refractive maps were used to evaluate relationships among variables of the HDS and refractive error. RESULTS: Myopic spherical equivalent refraction (P = .0003) and more negative asphericity (Q-values) (P = .0119) were correlated with steeper corneas. The Q-values were less negative in eyes with moderate myopia (2.0 to 6.0 diopters [D]) than in those with hyperopia (1.0 D or greater). The Q-values below -0.3 were correlated with less favorable values for predicted corneal acuity and corneal uniformity index values. Mean corneal curvature measurements obtained by computerized videokeratography and standard keratometry showed a strong degree of correlation (P = .0001). CONCLUSION: As the degree of myopia and negative asphericity increased, the corneal radius of curvature decreased. Corneal Q-values less than -0.3 were associated with reduced optical performance of the cornea.

Adolescent↗
PubMed1999

Comparison of contact lens overrefraction and standard keratometry for measuring corneal curvature in eyes with lenticular opacity.

PURPOSE: To assess the accuracy of corneal power measurement by contact lens overrefraction in patients with normal corneas and to determine the suitability of this method for use in intraocular lens (IOL) calculations. SETTING: General ophthalmology clinic at a public hospital (Ben Taub General Hospital, Houston, Texas, USA). METHODS: Using contact lens overrefraction (CLO), and standard keratometry, the corneal power in 33 eyes of 20 normal patients and patients scheduled for cataract extraction was prospectively measured. The eyes were divided into 3 groups based on their best spectacle-corrected visual acuity: (1) 20/20 to 20/40, (2) 20/50 to 20/70, and (3) 20/80 to 20/400. For each group, the means (absolute and arithmetic), standard deviations, and ranges of differences in corneal power as measured by CLO and keratometry were calculated. These values were used to estimate the induced variance in refractive outcome for IOL calculations. RESULTS: The mean absolute differences in corneal power by group were 0.35 diopter (D) +/- 0.18 (SD), 0.54 +/- 0.33 D, and 0.77 +/- 0.28 D, respectively. The mean arithmetic differences in corneal power were -0.05 +/- 0.39 D, +0.37 +/- 0.51 D, and +0.17 +/- 0.80 D, respectively. CONCLUSIONS: In eyes of patients with good visual acuity (20/20 to 20/40), corneal power measurements by CLO and keratometry were similar. The accuracy of the CLO-derived value decreased with increasing media opacity but was still acceptable with acuity of 20/70. Contact lens overrefraction may be a viable alternative to refractive history and videokeratography for estimating true corneal power in patients with surgically altered or irregular corneas.

Cataract↗
PubMed1999

Preoperative screening of contact lens wearers before refractive surgery.

PURPOSE: To evaluate corneal stability, measured by computerized videokeratography (CVK) after discontinuation of contact lens wear in preoperative refractive surgery candidates. SETTING: Baylor College of Medicine, Cullen Eye Institute, Houston, Texas, USA. METHODS: Topographic differences were analyzed in 136 noncontact lens wearers (NCLW) and 76 contact lens wearers (CLW) (18 rigid gas-permeable contact lenses [RGPCL], 58 soft contact lenses [SCL]) using EyeSys CVK after discontinuation of SCL wear for 2 weeks and RGPCL wear for 5 weeks. RESULTS: There were no differences in CVK patterns between the NCLW and the CLW groups. There were no statistically significant differences between the 2 groups in topographic symmetry, asphericity, corneal uniformity index, predicted corneal acuity, and irregular astigmatism. The dioptric range for the axial and the profile difference maps in the CLW group was slightly lower than in the NCLW group. CONCLUSIONS: For patients whose manifest refraction and CVK maps were within 0.5 diopters of earlier values, discontinuation of SCL wear for 2 weeks and RGPCL wear for 5 weeks was adequate for the cornea to return to its baseline topographic state.

Adult↗
PubMed1999

Corneal topography classification in myopic eyes based on axial, instantaneous, refractive, and profile difference maps.

PURPOSE: To refine and develop systems for classifying the topography of myopic corneas using axial, instantaneous, refractive, and profile difference maps. SETTING: Baylor College of Medicine, Cullen Eye Institute Houston, Texas, USA. METHODS: Using the EyeSys Corneal Analysis System, computerized videokeratographs of 153 corneas of 78 myopic patients were retrospectively analyzed. Patterns were defined with respect to the mid-dioptric green color. Relationships among pattern types, refractive power, corneal power, corneal uniformity index (CU index), and predicted corneal visual acuity (PC acuity) were calculated. RESULTS: Six types of patterns for axial, instantaneous, and refractive maps and 3 types of patterns for the profile difference map were defined. For a given cornea, there was a weak correlation among the patterns in the axial, instantaneous, and profile difference maps. The circular with central irregularity pattern in auto-scale refractive maps and the irregular pattern in profile difference maps and axial maps were correlated with lower CU index and PC acuity values. Clinical classification of instantaneous maps did not contribute substantially to the information provided by axial maps. CONCLUSION: Patterns of computerized videokeratographs varied according to the type of topographic map. The classification systems used provide a baseline for analyzing the response of the cornea to various interventions.

Adult↗
PubMed1999

Functional improvement after phacoemulsification cataract surgery.

PURPOSE: To evaluate subjective functional visual improvement after phacoemulsification and intraocular lens (IOL) implantation and identify patient characteristics and treatment features associated with no functional improvement. SETTING: Academic referral practice, Cullen Eye Institute, Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, USA. METHODS: A retrospective review was performed of the surgical results in 106 consecutive eyes of 102 patients who completed the American Society of Cataract and Refractive Surgery (ASCRS) Cataract Data Collection Form preoperatively and 1 month postoperatively. One surgeon performed all the surgery. The relationship of patient characteristics and treatment features and reported visual function was analyzed using an analysis of variance and the Wilcoxon rank sum and Fisher exact tests. RESULTS: One month postoperatively, all patients demonstrated improved visual acuity. However, 15 patients (14%) reported unimproved or decreased visual function. No statistically significant intergroup difference (P > .05) was detected in mean preoperative, postoperative, and fellow eye best spectacle-corrected visual acuities or refractive errors; reported severity of preoperative symptoms or satisfaction with vision; reported preoperative daily activity functioning or prevalence of hypertension and diabetes; type of anesthesia, lens material, or wound closure used; intraoperative or postoperative complication rates. However, patients reporting unimproved vision tended to be older and less satisfied with their quality of life and medical care than those reporting improved vision (P = .02, .03, .01, respectively). CONCLUSIONS: Self-reported visual function generally improved after phacoemulsification and IOL implantation; however, some older patients less satisfied with their quality of life and medical care reported no functional improvement despite improved visual acuity. These patients might benefit from an extended preoperative discussion of postoperative expectations.

Activities of Daily Living↗
PubMed1999

Pediatric cataracts.

There have been major changes over the past 5 to 10 years in our understanding of both the chemical basis for and the surgical treatment of cataract in infants and children. Important questions that remain to be answered include the appropriate power and design selection criteria for intraocular lens implantation, as well as management of the posterior capsule and long-term refractive sequelae. In the past 10 years, there have been radical changes in the management of visually significant cataract in the infant and child. Whereas lens removal, subtotal posterior capsulectomy, vitrectomy, and aphakia were once the standard of care, many physicians now feel that small incisions, phacoemulsification technology, and intraocular lenses (IOLs) are best for these patients. Work is continuing to accumulate a significant body of evidence to evaluate results of these changes in technique and to develop optimal IOL designs and selection criteria for these specialized cataract patients.

Adolescent↗
PubMed1999

Corneal topographic changes induced by excision of perilimbal lesions.

BACKGROUND AND OBJECTIVES: To evaluate corneal topographic changes induced by excision of two pterygia and a perilimbal dermoid. MATERIAL AND METHODS: Using the EyeSys Corneal Analysis System, we retrospectively analyzed the changes in astigmatism, mean central corneal power, and other topographic parameters of three corneas before and after surgical removal of two pterygia and a perilimbal dermoid. RESULTS: Marked corneal steepening occurred along the preoperative flat meridian after the excision of the pterygia and dermoid cyst. For each patient, surgery increased the mean central corneal curvature and decreased total astigmatism. CONCLUSION: Surgical excision can ameliorate abnormal corneal topographic changes produced by limbal lesions.

Adult↗
PubMed1998

Experimental and clinical evaluation of incision size and shape following forceps and injector implantation of a three-piece high-refractive-index silicone intraocular lens.

BACKGROUND: Previous studies have demonstrated that incision sizes required for insertion of various foldable intraocular lenses (IOLs) vary according to the IOL/inserter combination. The purpose of this study was to compare incision sizes and wound shape for both forceps and injector implantation of high-refractive-index silicone IOLs. METHODS: In fresh human cadaver eyes, limbal corneal tunnel incisions were created, and 12 foldable high-refractive-index silicone (dimethyldiphenylsiloxane) IOLs were inserted in a randomized fashion using either a forceps or an injector. Using incision calipers, internal and external measurements of the tunnel incisions were obtained before and after IOL insertion. Scanning electron microscopy (SEM) was performed on selected corneas following IOL insertion. Additionally, in 12 cataract procedures, the incision sizes following forceps or injector implantation were evaluated intraoperatively. RESULTS: In the experimental setting, the external and internal tunnel widths (in mm) before insertion were 3.05 mm (+/-0.07) and 3.02 mm (+/-0.03), respectively, with the forceps and 3.06 mm (+/-0.04) and 3.01 mm (+/-0.04) with the injector. Following IOL implantation, the external and internal incision sizes were 3.33 mm (+/-0.07) and 3.33 mm (+/-0.04) with the forceps and 3.32 mm (+/-0.08) and 3.33 mm (+/-0.07) with the injector. SEM showed tearing of corneal structures after implantation through the smallest possible incisions with both devices. In the clinical study, the incision sizes before and after implantation were 3.23 mm (+/-0.10) and 3.36 mm (+/-0.06) with the forceps and 3.11 mm (+/-0.08) and 3.21 mm (+/-0.10) with the injector. CONCLUSIONS: This study confirms that high-refractive-index silicone IOLs provide one of the smallest currently achievable incisions before and after IOL implantation. In clinical use, the new injector reduces the mean incision size required by approximately 0.1 mm.

Aged↗
PubMed1998

Axial, instantaneous, and refractive formulas in computerized videokeratography of normal corneas.

PURPOSE: To compare the values for corneal power determined by the axial, instantaneous and refractive formulas when imaging normal human corneas using computerized videokeratography. SETTING: Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. METHODS: This prospective clinical trial involved 60 corneas of 30 normal volunteers. Computerized videokeratography was performed to determine corneal power at the center and the 1, 3, 5, and 7 mm zones using the 3 formulas. RESULTS: Mean central corneal power was 42.86 diopters (D) with each of the formulas. The mean corneal powers for the axial, instantaneous, and refractive formulas were 43.09, 43.21, and 42.98 D at the 1 mm zone; 43.10, 42.92, and 43.46 D at the 3 mm zone; 42.75, 41.63, and 44.02 at the 5 mm zone; 42.21, 40.30, and 44.79 D at the 7 mm zone, respectively. The differences among powers for the 3 formulas at the 3, 5, and 7 mm zones were statistically significant (P < .01). CONCLUSION: In normal corneas, clinically significant differences exist in the corneal power values calculated by the axial, instantaneous, and refractive formulas.

Adolescent↗
PubMed1998

Radial and staggered treatment patterns to correct hyperopia using noncontact holmium:YAG laser thermal keratoplasty.

PURPOSE: To compare the effects of two treatment patterns in the correction of hyperopia by noncontact holmium:YAG laser thermal keratoplasty (LTK). SETTING: Divisione Oculistica, Ospedale S. Gerardo, Monza, Italy. METHODS: Using two treatment patterns, we performed noncontact LTK in one session in 16 eyes of 8 patients with isometropic hyperopic refractive errors; mean preoperative subjective cycloplegic refraction was +4.90 diopters (D) +/- 1.17 (SD). The treatment consisted of 24 spots in three concentric rings of eight spots each; ring diameters were 6.0, 7.0, and 8.0 mm, respectively. Each spot received seven pulses of laser energy at 30 mJ/pulse. We treated one eye of each patient with a radial pattern (the spots of the three rings aligned on the eight semimeridians) and the fellow eye with a staggered pattern (the spots of the contiguous rings at 22.5 degrees from each other). Follow-up at 1, 15, 30, 90, 180, and 360 days included subjective cycloplegic refraction, uncorrected (UCVA) and spectacle-corrected visual acuity (SCVA), computerized videokeratography (CVK), and Scheimpflug camera examination. RESULTS: One year postoperatively, the mean subjective cycloplegic refraction was +2.75 +/- 1.6 D in the eyes treated with the radial pattern and +3.40 +/- 1.6 D in those treated with the staggered pattern; the mean change in subjective cycloplegic refraction was 2.15 and 1.50 D, respectively. Mean UCVA improved by five lines in the radial group and by four lines in the staggered group. Mean SCVA returned to preoperative levels by day 15 in the radial group and at 1 year in the staggered group; at 1 year, SCVA improved by one line in the radial group and remained unchanged in the staggered group. No eye lost one or more lines of SCVA. Refractive astigmatism was essentially unchanged in both groups. Scheimpflug photography and CVK indicated larger and more uniform corrected zones in the radial group. CONCLUSIONS: Radial and staggered patterns effectively corrected low hyperopia, although both were subject to a certain amount of regression. The radial pattern produced faster postoperative recovery of SCVA and demonstrated greater refractive stability.

Adult↗
PubMed1998

Evaluating and reporting astigmatism for individual and aggregate data.

PURPOSE: To demonstrate the proper method for evaluating and reporting astigmatism for individual and aggregate data. SETTING: University of Texas Medical School and Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. METHODS: The surgically induced refractive change (SIRC) was determined for three data sets of patients who have had keratorefractive (photorefractive keratectomy) or cataract surgery. To make changes in refraction comparable, vertex distances for the refractions and keratometric index of refraction were considered. Doubledangle plots and single-angle plots were then used to display the data. Polar values (cylinder and axis) were converted to a Cartesian (x and y) coordinate system to determine the mean value of the induced astigmatism for each data set. RESULTS: Doubled-angle plots clearly demonstrated the trends of induced astigmatism for each data set, and the mean value for induced astigmatism agreed exactly with the intuitive appearance of the plot. CONCLUSIONS: Converting astigmatism data to a Cartesian coordinate system allowed the correct computation of descriptive statistics such as mean values, standard deviations, and correlation coefficients. Using doubled-angle plots to display the data provides the investigator with the best method of recognizing trends in the data.

Astigmatism↗
PubMed1998

Peripheral radial incisions to treat inferior contact lens edge lift after penetrating keratoplasty for keratoconus.

A patient with marked corneal astigmatism and inferior contact edge lift after penetrating keratoplasty for keratoconus had corneal relaxing incisions (CRIs) on the donor button and radial incisions on the host cornea. Results were evaluated by computerized videokeratography and by refitting the contact lens. Two pairs of CRIs decreased astigmatism from 11.00 to 4.25 diopters but did not alleviate the contact lens edge lift, which was caused by excessive steepness in the keratoconic host cornea. After 6 radial incisions were made to flatten the inferior host cornea, the peripheral cornea flattened and the patient was successfully refitted with a contact lens.

Astigmatism↗
PubMed1998

Effect of heparin in irrigating solution on inflammation following small incision cataract surgery.

PURPOSE: To study the effect of heparin-sodium added to the irrigating solution on postoperative inflammation in patients having cataract surgery. SETTING: Department of Ophthalmology, University of Giessen, Giessen, Germany. METHODS: Seventy-two patients having phacoemulsification with posterior chamber intraocular lens (IOL) implantation were randomly assigned to receive regular irrigating solution or solution with heparin-sodium (final diluted concentration 10 IU/mL). In half the patients, poly(methyl methacrylate) (PMMA) IOLs were implanted and in half, foldable silicone IOLs. The patients were examined preoperatively, on days 1 and 3, and 1 year postoperatively. Postoperative inflammation was objectively evaluated by measurement of flare and cells using laser flare-cell photometry. RESULTS: The mean postoperative flare values were significantly lower in the groups with additional heparin-sodium at days 1 and 3 (P < . 01). Flare values were not significantly different 1 year postoperatively. Cell values for the heparin-treated groups were lower, but the difference did not reach statistical significance. Flare and cells values for the two IOL materials were not significantly different during the entire follow-up. CONCLUSION: Heparin-sodium added to the infusion solution during small incision cataract surgery reduced inflammation in the early postoperative period.

Aged↗
PubMed1998

Dehiscence of a radial keratotomy incision during clear corneal cataract surgery.

We report a case of dehiscence of a radial keratotomy (RK) incision caused by clear corneal cataract surgery. The patient had eight-incision RK in both eyes 9 months previously with enhancement surgery in the left eye 1 month later. Cataract surgery through a clear corneal incision was performed in the right eye and 1 month later, in the left. Surgery in the right eye was uneventful. However, during surgery in the left eye, dehiscence of one radial incision occurred. The wound dehiscence was closed with interrupted sutures, and the patient achieved 20/20, uncorrected visual acuity 1 week after surgery.

Cornea↗