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Biomedical subjects

D D Koch

Publications and source records attributed to D D Koch.

At least 73 records · Page 4Linked to original sources
PubMed1996

Hyperopia correction by noncontact holmium:YAG laser thermal keratoplasty. Clinical study with two-year follow-up.

BACKGROUND: Thermal keratoplasty to correct hyperopia has been attempted with nonlaser and laser devices. Problems have included long-term regression and irregular induced astigmatism. The present clinical study was performed to investigate the safety, efficacy, and stability of a noncontact mode of holmium: YAG laser energy delivery and a modified laser thermal keratoplasty treatment procedure for correction of low hyperopia. METHODS: Seventeen patients underwent noncontact holmium: YAG laser thermal keratoplasty in their nondominant eyes for correction of hyperopia of up to 3.00 diopters. Treatment parameters included simultaneous delivery of eight holmium: YAG laser spots in a symmetrical octagonal array with a centerline diameter of 6mm, 10 pulses of laser light at 5-Hz pulse repetition frequency, and pulse energies of 159 to 199mJ. Follow-up was 2 years in 15 of 17 patients. RESULTS: In the 15 eyes examined at 2 years after surgery, mean uncorrected distance Snellen visual acuity improved from 20/125-1 to 20/50-2. The mean change in spherical equivalent of subjective manifest refraction was -0.79 diopter. Eleven of these 15 eyes (73%) had a mean refractive correction of -1.1 diopters (range, -0.38 to -2.63 diopters); regression between 14 days and 2 years was 0.2 diopter. Four eyes (27%) had no persistent refractive correction (within +/- 0.25 diopter). Mean induced refractive astigmatism was 0.18 diopter. None of the eyes lost two or more lines of spectacle-corrected distance vision. The amount of refractive correction at 2 years after surgery was correlated to the treatment pulse energy and the volume of the opacified corneal tissue observed immediately after treatment. CONCLUSIONS: This technique of noncontact laser thermal keratoplasty produced safe, effective, and persistent corrections of low hyperopia in the majority of treated eyes.

Aged↗
PubMed1996

Changes in pupil size induced by phacoemulsification and posterior chamber lens implantation: consequences for multifocal lenses.

PURPOSE: Because the optical performance of eyes implanted with multifocal intraocular lenses will theoretically depend upon the size and position of the pupil relative to the near and distance zones of the lens, we designed a study to determine whether preoperative pupil size is useful in predicting the postoperative pupil size of patients having phacoemulsification with posterior chamber lens implantation. SETTING: Cullen Eye Institute, Department of Ophthalmology, Baylor College of Medicine, Houston, Texas. METHODS: We prospectively measured pupil sizes preoperatively and postoperatively in 71 consecutive patients who had phacoemulsification with posterior chamber lens implantation. Pupil sizes were photographed under five lighting and viewing conditions that simulated a range of normal functional situations. RESULTS: The mean change in preoperative to postoperative pupil size was less than 0.5 mm in all five testing conditions. However, changes in pupil diameter of 1.0 mm or more were noted in approximately 10% of patients in each testing situation. Sex, iris color, and the presence or absence of intraoperative iris trauma were not predictive factors for determining which patients sustained large postoperative changes in pupil size. CONCLUSIONS: Preoperative pupil size does not predict postoperative size with sufficient consistency to ensure a good match between pupil diameter and the zone sizes of multizone multifocal intraocular lenses.

Follow-Up Studies↗
PubMed1996

Corneal topographic changes after noncontact holmium:YAG laser thermal keratoplasty to correct hyperopia.

PURPOSE: To analyze the changes in corneal curvature induced by laser thermal keratoplasty (LTK) to correct hyperopia. SETTING: Cullen Eye Institute, Baylor College of Medicine, Houston, Texas. METHODS: We performed LTK on nine hyperopic eyes using a noncontact holmium: YAG (Ho:YAG) laser. Five eyes received a single ring of eight spots at the 6 mm zone (Group A); four received a second ring of eight at the 7mm zone (Group B). Computerized videokeratography (CVK) was obtained preoperatively and 1, 30, 90, 180, and 360 days postoperatively. We calculated the net dioptric changes in the following CVK values: corneal curvature at the 1, 3, 5, and 7 mm zones; effective corneal refractive power (Eff RP); and spherical equivalent of subjective manifest refraction (SE SMR). We classified difference maps according to the pattern of induced change. RESULTS: At 1 year, steepening at the 1, 3, 5, and 7 mm CVK zones was 0.5 diopter (D), 0.6 D, 0.1 D, and -0.42 D, respectively, in Group A and 1.5 D, 1.5 D, 1.1 D, and 0.54 D, respectively, in Group B. Effective corneal refractive power increased 0.6 D in Group A and 1.5 D in Group B. Mean change in SE SMR was -0.6 D in Group A and -1.4 D in Group B. Most regression occurred during the first 90 days. Difference maps showed five bow-tie, two irregularly irregular, one semicircular, and one homogeneous patterns. CONCLUSIONS: Noncontact Ho:YAG LTK produced peripheral corneal flattening and central corneal steepening. A greater change in curvature was produced using a two-ring treatment.

Adult↗
PubMed1996

Scanning electron microscopic analysis of foldable acrylic and hydrogel intraocular lenses.

OBJECTIVE: To analyze the surface quality of foldable acrylic and hydrogel intraocular lenses (IOLs). SETTING: Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, and Institute of Anatomy and Cellular Biology, University of Giessen, Germany. METHODS: We studied eight foldable IOL models with optics made of six different acrylate/methacrylate polymers: Acrylens ACR360 (loptex), AcrySof MA60BM (Alcon), MemoryLens U940A (Mentor), 92S and 92C (Morcher), Hydroview H60M (Storz), HydroSof SH30BC (Alcon), and ISH66 (Corneal). Four IOLs of each design were examined. Light and scanning electron microscopy were performed before and after IOL folding with forceps. RESULTS: All IOL models had excellent optic and haptic surfaces. The haptic-optic junctions revealed minimal empty spaces or irregularities in three of the five three-piece IOLs and smooth surfaces in all one-piece IOLs. Minimal surface alterations and superficial defects caused by folding were detectable in the two acrylate (acrylic) IOLs (loptex ACR360, Alcon MA60BM) with low water content. CONCLUSION: Intraocular lenses of acrylate/methacrylate polymers had excellent surface quality. The acrylic IOLs were vulnerable to mild folding or forceps defects; however, these were less marked than those previously noted with poly(methyl methacrylate) IOLs.

Lenses, Intraocular↗
PubMed1996

Evaluation of intraocular pressure with Healon and Healon GV in sutureless cataract surgery with foldable lens implantation.

PURPOSE: To evaluate transient increases in intraocular pressure (IOP) after use of high-viscosity viscoelastic agents in cataract surgery. SETTING: Military Hospital, Ulm, Germany. METHODS: In a prospective, randomized study, we evaluated IOP following cataract surgery using two different viscoelastic substances (Healon, Healon GV). The viscosity of Healon GV is 10 times higher than that of Healon because of higher concentration and molecular weight. Patients having identical phacoemulsification procedures (sutureless clear corneal tunnel incision with foldable silicone lens implantation) (N = 60) and identical viscoelastic removal were assigned to groups of 15 based on viscoelastic used and removal time (20 or 40 seconds). Intraocular pressure was measured preoperatively and at 6, 24, 36, and 48 hours and 1 month postoperatively. RESULTS: The highest mean IOP elevations in both viscoelastic groups were obtained at 24 hours postoperatively (2.9 mm Hg +/- 4.3 [SD] with Healon and 3.3 +/- 6.3 mm Hg with Healon GV). There were no statistically significant differences between the two viscoelastics and the two removal times during the entire follow-up period (unpaired t-test), but standard deviations were higher in the Healon GV groups at 6 and 24 hours. Two patients in the Healon groups and three in the Healon GV groups required medical treatment for IOP within the first 24 postoperative hours; however, all five patients had an IOP lower than 22 mm Hg on the second postoperative day. CONCLUSIONS: Based on postoperative IOP, both viscoelastics can be equally well removed from the anterior chamber. Incidence of high IOP using high-viscosity hyaluronic acid is minimized by the described removal technique.

Aged↗
PubMed1996

Computerized videokeratography and keratometry in determining intraocular lens calculations.

PURPOSE: To compare the accuracy of standard keratometry and computerized videokeratography (CVK) in determining intraocular lens (IOL) power calculations. METHODS: Using the EyeSys Corneal Analysis System, we prospectively obtained CVK maps on 75 eyes of 69 patients scheduled to have phacoemulsification with implantation of a posterior chamber intraocular lens. Using manifest refraction obtained at 6 weeks postoperatively, we optimized the calculations for the Hoffer Q, Holladay, and SRK/T formulas for standard keratometric and the following six CVK values: average curvatures at the 1 mm, 2 mm, and 3 mm zones, the keratometric equivalent at the 3 mm zone, and the Stiles-Crawford weighted averages over the 3 mm and 6 mm zones. The accuracy of these parameters was determined by calculating the mean absolute error and percentage of patients with accuracy within < or = 0.5 diopter (D), < or = 1.0 D, and < or = 2.0 D. RESULTS: Keratometrically derived data were slightly more accurate than the CVK-derived values. The average difference in mean absolute error between the keratometric and CVK values was 0.13 D for the Hoffer Q formula, 0.11 D for the Holladay, and 0.08 D for the SRK/T. CONCLUSIONS: In this population of patients, we found the CVK-derived corneal curvature values to be slightly less accurate than standard keratometry in predicting IOL power. However, CVK provides important corneal curvature data for IOL calculations in patients with abnormal or surgically altered corneal surfaces.

Anthropometry↗
PubMed1996

Methods to control astigmatism in cataract surgery.

The correction of astigmatism during cataract surgery has evolved due to recent basic and clinical studies. To control surgically induced astigmatism, the surgeon has many options, including varying incision parameters, astigmatic keratotomy, scleral flap recession and resection, toric intraocular lens implantation, and modifying postoperative medical treatment. The recent literature is reviewed, and our current approach for cataract surgery is discussed.

Astigmatism↗
PubMed1996

How to evaluate and implement new technologies in an era of managed care and cost containment.

New technologies often enable clinical laboratorians to overcome the challenges we face. These technologies sometimes become available with amazing punctuality, addressing recent problems and keeping the physician-customer satisfied for another day. Traditionally, developments such as a new cancer marker have been implemented into routine use with little circumspection because the benefits diagnostically and financially were perceived to far outweigh the risk that the new test or technology was not as effective as described. The notion of subsequently removing older tests inferior to the new one has hardly been considered. The challenges confronting clinical laboratorians today, however, are affecting that typical pattern dramatically. Four of the most pervasive challenges are comprehensively examined in the 1995 Clinical Chemistry Forum. One of these key areas--the proper implementation of modern technology in the form of new tests or new approaches to producing clinical laboratory results--is the main topic of this review.

Chemistry, Clinical↗
PubMed1996

Enter with caution.

Explore the source record for details and available documents.

Anterior Chamber↗
PubMed1996

Corneal topographic changes and induced astigmatism resulting from superior and temporal scleral pocket incisions.

BACKGROUND AND OBJECTIVE: To determine the corneal topographic changes that are induced by superior and temporal 5-mm scleral pocket incisions. PATIENTS AND METHODS: The authors retrospectively reviewed the records of 43 patients who underwent phacoemulsification with posterior chamber lens implantation through unsutured 5-mm scleral pocket incisions, 24 superiorly and 19 temporally. Corneal curvature was measured using computerized videokeratography, and the induced astigmatism was calculated with the Holladay-Cravy-Koch formula. RESULTS: At 4 to 6 weeks, postoperatively there was mild flattening along with the meridian of the incision in both groups. The change was greater with the superior incisions, but the differences between the groups were not statistically significant. Surgically induced astigmatism was 0.7 D (+/-0.1 D) in the eyes that received superior incisions, and 0.3 D (+/-0.1 D) in the eyes that received temporal incisions; this difference was statistically significant (P < .03). CONCLUSIONS: At 4 to 6 weeks postoperatively, temporal 5.0-mm scleral pocket incisions provide more stable postoperative topography than do superior scleral pocket incisions.

Adult↗
PubMed1996

Secondary cataract formation following pediatric intraocular lens implantation: 6-month results.

Secondary membrane formation is the most common complication of posterior chamber intraocular lens (PC IOL) implantation in children. The purpose of this study was to determine the effect of various methods of managing the posterior capsule and anterior vitreous on the rate of posterior capsular opacification in children implanted with PC IOLs. We retrospectively studied 16 eyes of 12 children (age 1.5-12 years) implanted with PC IOLs; the follow-up period was at least 6 months. The posterior capsule and anterior vitreous were managed in a variety of ways: in 5 eyes the posterior capsule was left intact, and 11 eyes underwent posterior capsulorehexis (PCCC)-6 cases without and 5 cases with anterior vitrectomy. In two eyes of each of the last two groups, posterior optic capture was performed. Visually significant secondary cataract developed in all five eyes with intact posterior capsules and in the four eyes that had undergone PCCC without vitrectomy and without posterior optic capture. The optical axis remained clear in all eyes that had undergone vitrectomy and in all eyes treated with posterior optic capture. Each procedure, posterior optic capture and anterior vitrectomy appears to be effective in preventing or delaying posterior opacification in lens implantation in infants and children. However, a longterm follow-up is required to determine the efficacy and safety of these two approaches.

Cataract↗
PubMed1996

Hyperopia correction by noncontact holmium:YAG laser thermal keratoplasty. United States phase IIA clinical study with a 1-year follow-up.

PURPOSE: This study was performed to evaluate the safety and effectiveness of noncontact holmium: YAG (Ho:YAG) laser thermal keratoplasty (LTK) for correcting low to moderate hyperopia. METHODS: Twenty-eight patients were treated unilaterally to correct low to moderate hyperopia (up to +3.88 diopters [D] refractive error) using simultaneous noncontact delivery of Ho:YAG laser energy. Treatment parameters included one or two symmetric octagonal rings of eight spots per ring with centerline diameters of 6 mm (1 ring) or 6 and 7 mm (2 rings), ten pulses of laser light at 5-Hz pulse repetition frequency, and variable pulse energy, ranging from 208 to 242 mJ. Follow-up was 1 year in 26 (93%) of the 28 patients. RESULTS: At 1 year postoperatively, uncorrected distance visual acuity was improved in all patients. The mean change in subjective manifest refraction (+/- spherical equivalent [SE]) was -0.55 +/- 0.33 D and -1.64 +/- 0.61 D for one and two-ring treatment groups, respectively, with good stability in the refractive change after approximately 6 months. In the one-ring treatment group (17 eyes), refractive corrections of -0.50 to -1.13 D were achieved in ten eyes (59%), and seven eyes (41%) were unchanged (within +/- 0.25 D) relative to their preoperative measurements. In the two-ring treatment group, all eight eyes (100%) had substantial refractive corrections (range, -0.75 to -2.50 D). Mean induced refractive astigmatism was 0.25 +/- 0.29 D and 0.47 +/- 0.53 D for one- and two-ring treatments, respectively. None of the eyes lost two or more lines of spectacle-corrected distance visual acuity. These was no clinically significant change in endothelial cell density with respect to preoperative values. Glare and contrast sensitivity testing indicate that peripheral corneal opacities produced by LTK do not degrade vision. The amount of refractive change in each group was correlated with the amount of laser pulse energy. CONCLUSIONS: This initial United States clinical study with 1-year follow-up indicates that noncontact LTK treatment of low hyperopia is safe and effective, providing persistent, though modest, refractive corrections in 59% of the one-ring group and larger, persistent, refractive corrections in 100% of the two-ring group.

Adult↗
PubMed1996

Histological changes and wound healing response following noncontact holmium: YAG laser thermal keratoplasty.

PURPOSE: To evaluate acute histological changes and the induced wound healing response in corneal tissue following noncontact holmium:YAG laser thermal keratoplasty (LTK). METHODS: LTK using 10 pulses and a range of radiant energies was performed on 3 human corneas one day prior ro their removal at penetrating keratoplasty. Rabbit corneas were treated with 10-pulse and 5-pulse LTK and followed for up to 3 months. Tissues were studies with light and transmission electron microscopy and immunohistochemistry. RESULTS: The amount of acute tissue injury increased with increasing pulse radiant energy. In human corneas, changes in the irradiated zones included epithelial cell injury and death loss of fine filamentous structure in Bowman's layer, disruption of stromal lamallae, and keratocyte injury and death. In the rabbit corneas, similar acute changes were noted. By 3 weeks, epithelial hyperplasia and stromal contraction were present. Wound healing in the rabbit corneas included repair of the epithelial attachment complex, keratocyte activation, synthesis of type I collagen, partial restoration of stromal keratan sulfate and type VI collagen, and retrocorneal membrane formation. Compared to 10-pulse treatments, 5-pulse treatments produced less acute tissue injury and had more rapid restoration of normal stromal architecture. CONCLUSION: Noncontact LTK produces acute epithelial and stromal tissue changes and in rabbit corneas stimulates a brisk wound healing response. These changes could contribute to postoperative regression of induced refractive correction. Further work is required to determine if reductions in the magnitude of acute tissue injury and induced wound healing response will enhance the efficacy and stability of LTK.

Animals↗
PubMed1995

Topical anesthesia for phacoemulsification: initial 20-case series with one month follow-up.

We report the results of our initial 20 phacoemulsification cases performed using topical anesthesia. The preferred topical regimen consisted of preservative-free 0.75% bupivacaine. Intravenous sedation was provided primarily with fentanyl and midazolam. Phacoemulsification was performed through a scleral tunnel incision, and a one-piece poly(methyl methacrylate) or three-piece silicone intraocular lens was implanted. There were no complications with the anesthetic technique. One day postoperatively, 69% of patients with a desired refractive error within 0.75 diopters of emmetropia had an uncorrected visual acuity of 20/40 or better. At one month, all patients had a best corrected acuity of 20/30 or better, and 60%, 20/20 or better. Eighteen patients reported complete intraoperative comfort, and 17 reported complete postoperative comfort. Seven of the 10 patients who had had previous peribulbar anesthesia preferred topical. All 10 "first eye" patients said they would choose topical anesthesia for future surgery. With appropriate case selection, topical anesthesia for phacoemulsification surgery can be used with excellent intraoperative and postoperative results.

Anesthesia, Local↗