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Biomedical subjects

D D Koch

Publications and source records attributed to D D Koch.

At least 55 records · Page 3Linked to original sources
PubMed1998

The Baylor survey of Ophthalmology Residency graduates: rationale for reform in residency training.

BACKGROUND AND OBJECTIVE: To survey graduates of an ophthalmology residency training program regarding skills necessary for a well-trained ophthalmologist. METHODS: Two survey instruments were mailed to the graduates of the Baylor College of Medicine Department of Ophthalmology Residency Training Program. RESULTS: Specific skills were identified that were rated as clinically important and for which training was considered adequate, and, conversely, skills that were rated as less important but for which training was adequate. CONCLUSION: This survey instrument may allow ophthalmology residency training programs to identify perceived and real deficiencies in the prioritization of changes in curriculum or the skills transfer process.

Clinical Competence↗
PubMed1997

Homocysteine: a new risk factor for atherosclerosis.

The accumulating evidence for the role of homocysteine as a risk factor for atherosclerosis is persuasive. A high plasma homocysteine concentration induces pathologic changes in the arterial wall and thus is strongly associated with an increased risk of atherosclerosis, manifested as cardiovascular, cerebrovascular and peripheral vascular events. Studies are being conducted to determine whether lowering homocysteine levels prevents occlusive events. At present, testing for elevated homocysteine concentrations should be considered in patients with premature atherosclerosis or a strong family history of atherosclerosis, since hyperhomocysteinemia is a common risk factor in these patients. Treatment of hyperhomocysteinemia is straightforward and associated with minimal risk. This disorder is usually correctable with vitamin supplements containing folic acid.

Algorithms↗
PubMed1997

Acute and chronic conjunctivitis due to over-the-counter ophthalmic decongestants.

OBJECTIVE: To describe patterns of conjunctivitis caused by ophthalmic decongestants. DESIGN: Case series. SETTING: Outpatient eye clinic. PATIENTS: We selected patients with conjunctival inflammation who were using nonprescription decongestant eyedrops, who had no other cause for conjunctivitis, and whose conditions improved after discontinuing the incriminated preparations. MAIN OUTCOME MEASURES: Clinical characteristics of conjunctival inflammation and time to resolution of symptoms and signs after discontinuing the use of eyedrops. RESULTS: Seventy patients (137 eyes) were identified. Preparations containing the vasoconstrictors naphazoline, tetrahydrozoline, or phenylephrine were associated with 3 clinical patterns of conjunctivitis: conjunctival hyperemia (50 cases), follicular conjunctivitis (17 cases), and eczematoid blepharoconjunctivitis (3 cases). Decongestants were used daily for a median of 3 years (range, 8 hours to 20 years) prior to presentation. The median time to resolution of symptoms and signs was 4 weeks (range, 1-24 weeks), and patients remained asymptomatic for a median follow-up of 6 months (range, 0-12 years). CONCLUSION: Nonprescription decongestant eyedrops can produce acute and chronic forms of conjunctivitis by pharmacological, toxic, and allergic mechanisms. Once recognized, conjunctival inflammation often takes several weeks to resolve.

Acute Disease↗
PubMed1997

Hyperopia correction by noncontact holmium: YAG laser thermal keratoplasty: five-pulse treatments with 1-year follow-up.

BACKGROUND: Previous noncontact holmium (Ho): YAG laser thermal keratoplasty (LTK) studies on correction of low to moderate hyperopia have used treatment algorithms based on ten-pulse, variable-pulse-energy treatment parameters. The purpose of this study was to evaluate the safety, effectiveness, and stability of new five-pulse, constant-pulse-energy treatment parameters for noncontact Ho:YAG LTK. METHODS: Thirty-nine hyperopic patient eyes [up to +4.75 diopters (D) refractive error] were treated using simultaneous noncontact delivery of Ho:YAG laser energy (Sunrise) with two symmetrical octagonal rings of eight spots per ring and radial spot patterns on centerline diameters of 5 and 6 mm (group A), 6 and 7 mm (group B), or 6.5 and 7.5 mm (group C). Each ring of spots received five pulses of laser light at 5 Hz pulse repetition frequency and a fixed pulse energy of 240 mJ. Thirty of the 39 patient eyes (77%) had 1-year follow-up exams. RESULTS: At 1 year, the mean Snellen uncorrected distance visual acuity lines gained was 3.7 +/- 0.5/6.8 +/- 2.7/5.3 +/- 3.3 for groups A, B, and C. The mean changes in subjective manifest refraction (spherical equivalent) were -2.08 +/- 1.13 D, -1.83 +/- 0.88 D, -1.22 +/- 0.88 D for groups A, B, and C respectively. None of the eyes lost two or more lines of spectacle-corrected distance visual acuity. There were no clinically significant complications in any patient. CONCLUSION: This clinical study indicates that five-pulse noncontact LTK treatments of low hyperopia are safe and effective. The stability has to be confirmed with longer follow-up.

Adult↗
PubMed1997

[Assessment of refractive difference after photorefractive keratectomy. A comparison between keratometry and computer-assisted video keratography].

UNLABELLED: The purpose of this study was to determine which corneal curvature values most closely correlated to change in subjective manifest refraction following excimer laser photorefractive keratectomy (PRK). METHODS: Excimer laser PRK was performed on ten eyes of ten patients (mean age: 37.3 years). Preoperative refractive errors ranged from -2.25 to -8.75 diopters. Preoperatively and 1 month postoperatively, we determined the spherical equivalent of the manifest refraction (corrected for a 12 mm vertex distance) and measured corneal power using standard keratometry (Bausch and Lomb keratometer) and computerized videokeratography (EyeSys Corneal Analysis System). We collected five corneal values: standard keratometry, videokeratography-derived simulated keratometric readings calculated using the axial, instantaneous and refractive formulas, and corneal refractive power over the central 3-mm zone (effective refractive power); apart from the traditional refractive index of the cornea (n = 1.3375), we used the refractive value of the anterior corneal stroma (n = 1.376). For each of the five corneal values, we subtracted the change in corneal power from the change in manifest refraction and calculated the means and standard deviations. RESULTS: The mean differences between the refraction and the corneal values for a refractive index of 1.3375/1.376 were: 0.89 +/- 0.54*/1.26 +/- 0.59* for standard keratometry; 1.64 +/- 0.75*/1.37 +/- 0.7*, 4.03 +/- 1.86*/ 3.86 +/- 1.87*, and 1.16 +/- 0.76*/0.91 +/- 0.74* for the axial, instantaneous, and refractive videokeratography values, respectively; and 0.83 +/- 1.03*/0.39 +/- 1.08 for the effective refractive power (*,p < 0.05). CONCLUSIONS: In our series, only the values for the effective refractive power, calculated with the refractive Index of the anterior stroma of the cornea, were not statistically different from the change in manifest refraction.

Adult↗
PubMed1997

Hyperopia correction by noncontact holmium:YAG laser thermal keratoplasty: U.S. phase IIA clinical study with 2-year follow-up.

PURPOSE: This study was performed to determine the long-term efficacy, safety, and stability of noncontact holmium:yttrium aluminum garnet (Ho:YAG) laser thermal keratoplasty (LTK) for correction of low-to-moderate hyperopia. METHODS: The authors treated 1 eye each of 28 patients for correction of low-to-moderate hyperopia (up to +3.88 diopters [D] refractive error) using the Sun 1000 Corneal Shaping System (Sunrise Technologies, Inc., Fremont, CA). Treatments were performed with one or two rings of eight spots per ring with centerline diameters of 6 mm (one ring) or 6 and 7 mm (two rings), ten pulses of laser light at 5-Hz pulse repetition frequency, and pulse energies ranging from 208 to 242 mJ. Follow-up was 2 years. RESULTS: At 2 years after surgery, uncorrected distance visual acuity was improved by 1 or more lines of Snellen visual acuity in 19 (73%) of 26 of the treated eyes. The mean lines gained was 2.5 +/- 2.2/3.3 +/- 2.7 for one- and two-ring treatment groups, respectively. The mean change in spherical equivalent of the subjective manifest refraction was -0.53 +/- 0.33 D/-1.48 +/- 0.58 D for one- and two-ring treatment groups. Regression between 1 and 2 years was 0.01 D and 0.16 D, respectively. In the one-ring treatment group (18 eyes), 13 eyes (72%) had refractive corrections (range, -0.38 to -1.13 D), and 5 eyes (29%) were unchanged (within +0.25 D) relative to their preoperative measurements. In the two-ring treatment group, all eight eyes (100%) had reductions in their hyperopia (range of corrections, -0.38 to -2.25 D). None of the eyes lost two or more lines of spectacle-corrected distance visual acuity. There were no sight-threatening complications. CONCLUSIONS: This initial U.S. clinical study indicates that noncontact laser thermal keratoplasty treatment of low hyperopia is safe and produces modest but persistent corrections with 2-year follow-up. Expanded studies of this treatment method are warranted.

Adult↗
PubMed1997

Lensification of the posterior corneal surface. An unusual proliferation of lens epithelial cells.

BACKGROUND: Abnormal proliferation of lens epithelial cells occurs in a variety of situations, such as anterior and posterior subcapsular cataracts and secondary cataract formation. The purpose of this report is to document an unusual occurrence of diffuse proliferation of lens epithelium and capsule along the posterior corneal surface. METHODS: The authors performed penetrating keratoplasty to remove an edematous and scarred cornea is a 19-year-old Indian man. Three years previously, the patient had undergone penetrating keratoplasty and extracapsular cataract extraction to treat a nonhealing corneal ulcer. The keratectomy specimen was processed for conventional light microscopy. Five-micrometer sections were stained with hematoxylin-eosin and the periodic acid-Schiff methods. RESULTS: Intraoperatively, the eye was found to be aphakic with an intact posterior capsule. The iris tissue consisted of fibrotic, pigmented remnants adherent to the peripheral cornea for 360 degrees, closing the angle and capsular fornix. Histologically, cataractous lens material including proliferated lens epithelial cells and capsule diffusely lined the posterior corneal surface along a thick retrocorneal fibrous membrane. CONCLUSIONS: This case represents a new category of lens epithelial cell proliferation or migration or both that covers entirely the posterior corneal surface. The authors believe the term lensification is appropriate for the condition described herein.

Adult↗
PubMed1997

Incision sizes for foldable intraocular lenses.

OBJECTIVE: The purpose of the study is to determine the minimal incision sizes required for implantation of a variety of different foldable intraocular lenses (IOLs) and to evaluate the effect of incision size on tissue damage. DESIGN: Randomized experimental study. PARTICIPANTS: Sixty-nine fresh human cadaveric eyes: 15 (pilot study), 48 (main study), and 6 (scanning electron microscopy study). INTERVENTION: Implantation of foldable IOLs into cadaveric eyes. MAIN OUTCOME MEASURES: In 48 fresh human cadaveric eyes, limbal corneal tunnel incisions were made, and in a randomized fashion, 8 different foldable IOLs of 20.5 diopters (D) were inserted: 4 silicone (SI-30NB, Allergan Medical Optics, Irvine, CA; C10UB, Chiron Ophthalmics, Inc, Irvine, CA; LI41U, IOLAB, Chiron Ophthalmics, Inc, Irvine, CA; AA-4203, Staar Surgical Company, Monrovia, CA); two soft acrylic (MA60BM and MA30BA, both Alcon Laboratories, Inc, Ft. Worth, TX); and two hydrogel models (SH30BC, Alcon; H60M, Storz Ophthalmics, Inc, St. Louis, MO). For each IOL model, six insertions were performed with a recommended implantation device. Using calipers, the authors measured internal and external incision sizes before and after insertion. Scanning electron microscopy was performed on selected incisions in six additional human cadaveric eyes. RESULTS: Incision sizes after insertion ranged from 3.2 to 3.8 mm. The smallest incisions permitting IOL insertion were associated with the injectors. However, these incisions enlarged after insertion by approximately 11% and then were similar to the incision sizes after forceps insertion of the high-refractive-index silicone, the 5.5-mm optic acrylic, and the one-piece hydrogel IOL. The largest incisions were associated with the 6-mm acrylic IOL and the three-piece silicone IOL with a lower refractive index. The scanning electron microscopy showed tearing of corneal tissue after implantation through the smallest incision; this was more pronounced with injectors than with forceps. CONCLUSIONS: Corneal tunnel incisions enlarged up to 11% after insertion of foldable IOLs through the smallest possible incision. With current technology, the smallest postinsertion incision size of a 20.5-D foldable IOL is 3.2 mm.

Cadaver↗
PubMed1997

Changes in computerized videokeratography induced by artificial tears.

PURPOSE: To analyze the effect of several standard artificial tear preparations on computerized videokeratographic measurements. SETTING: Cullen Eye Insitute, Baylor College of Medicine, Department of Ophthalmology, Houston, Texas, USA. METHODS: We evaluated one eye each in 18 normal volunteers. Using the EyeSys Corneal Analysis System (EyeSys Technologies), we obtained corneal topographic measurements at baseline and 0.5, 1, 2, 3, 4, 5, 6, 8, and 10 minutes after instillation of the following preparations: balanced salt solution, Tears Naturale II, Tears Naturale Free, Cellufresh, Celluvisc, HypoTears, and HypoTears PF. We analyzed changes in curvature of the keratographic rings at radii 1 to 5 mm and changes in keratometric-equivalent astigmatic power and meridian. RESULTS: All preparations except HypoTears and Tears Naturale II induced statistically significant, time-dependent changes in mean corneal power in the central 5 mm corneal zone compared with baseline measurements (P < .05). The relationship between change in dioptric power over time varied with preparation type and was nonlinear in nature. In all cases, the mean induced change was < or = 0.5 diopter. Except for Celluvisc, tear administration produced minimal changes in the values of corneal astigmatic power or meridian. CONCLUSION: When performing serial measurements of mean corneal power, the greatest consistency was achieved with no tears or with instillation of HypoTears or Tears Naturale II.

Astigmatism↗
PubMed1997

Levobunolol 0.5% and timolol 0.5% to prevent intraocular pressure elevation after neodymium:YAG laser posterior capsulotomy.

PURPOSE: To evaluate the prophylactic effect of levobunolol 0.5%, timolol 0.5%, or vehicle in reducing the incidence of postoperative intraocular pressure (IOP) spikes of 5 and 10 mm Hg or more in patients having neodymium:YAG (Nd:YAG) laser posterior capsulotomy. SETTING: Miami Vision Center, Coral Gables, Florida; Cullen Eye Institute, Baylor College of Medicine, Houston, Texas; Cincinnati Eye Institute, Cincinnati, Ohio; South Texas Cataract and Glaucoma Center, San Antonio, Texas; Mid-South Eye Foundation, Memphis, Tennessee, USA. METHODS: This prospective, double-masked, randomized study comprised 144 patients having Nd:YAG laser posterior capsulotomy in one eye. One drop of the test medication was administered preoperatively and one drop on the evening after surgery; IOP was measured preoperatively and 1,2,3 and 24 hours postoperatively. RESULTS: Intraocular pressure elevations of 5 mm Hg or more were seen in 1 of 60 patients (2%) in the levobunolol group, 4 of 54 (7%) in the timolol group, and 10 of 28 (36%) in the vehicle group. These elevations occurred significantly more frequently in the vehicle group than in the levobunolol (P < .001) or timolol (P < .004) groups. Elevations of 10 mm Hg or more were found in 2 of 28 patients (7%) treated with vehicle but were not observed in the patients treated with levobunolol or timolol. CONCLUSIONS: Levobunolol 0.5% or timolol 0.5% administered preoperatively and again in the evening after Nd:YAG laser capsulotomy effectively blunted the IOP rise that frequently follows laser surgery.

Adrenergic beta-Antagonists↗
PubMed1997

Epidemiological evidence for the disruption of ionized calcium homeostasis in the elderly.

Ionized calcium (Ca2+), phosphate, albumin, total calcium, and pH measurements taken from participants in a large population-based epidemiological study were examined to determine the change in physiological variation with age for persons over 43 years old. Only Ca2+ showed a statistically significant increase in SD with age (p < 0.0001). The Ca2+ coefficients of variation (CV) increased from 2.92% in the youngest age group (43-54 years) to 3.69% in the oldest age group (75-86 years of age). In females, the increase in Ca2+ variability was nearly complete by age 55. Males also showed a significant (p = 0.006) increase in SD between the 43-54 age group and the 55-64 age group, however, Ca2+ variability did not plateau after age 55 in men as it did in women. In the 43-54 (p = 0.04) and 55-64 (p = 0.03) age group men showed significantly better physiological control of Ca2+ than women. Phosphate showed a slight decrease in CV with age. These data suggest that Ca2+ homeostasis is disrupted in the same age groups that are most vulnerable to osteoporosis.

Adult↗
PubMed1997

Noncontact holmium:YAG laser thermal keratoplasty to correct hyperopia: 18-month follow-up.

PURPOSE: To assess the safety and efficacy of noncontact holmium:yttrium aluminium garnet laser thermal keratoplasty (Ho:YAG LTK) for correction of low to moderate hyperopia. METHODS: We performed noncontact Ho:YAG LTK on 1 eye each of 28 patients for correction of hyperopia up to +3.88 dpt. Treatments were conducted with 1 or 2 symmetrical octagonal rings of 8 spots/ring with centerline diameters of 6 mm (1 ring) or 6 and 7 mm (2 rings), 10 pulses of laser light at 5 Hz pulse repetition frequency, variable pulse energy in the range of 208-242 mJ and a nominal spot diameter between 615 and 623 microns. RESULTS: At 18 months after surgery, 20 of 22 (91%) treated patient eyes had improved uncorrected distance visual acuity. The mean change in subjective manifest refraction (spherical equivalent) was -0.52 +/- 0.35 dpt and -1.41 +/- 0.53 dpt for 1- and 2-ring treatment groups, respectively, with good stability in the refractive change after 6 months. The mean induced refractive astigmatism was small (0.30 +/- 0.37 dpt/0.25 +/- 0.29 dpt for 1-/2-ring treatments). None of the eyes lost 2 or more lines of spectacle-corrected distance visual acuity. There were no clinically significant changes in glare and contrast sensitivity. CONCLUSIONS: Noncontact LTK treatment of low hyperopia is safe and effective, and it is more stable and less prone to induce astigmatism than previously reported contact mode LTK treatments.

Adult↗
PubMed1997

Visual function following trabeculectomy: effect on corneal topography and contrast sensitivity.

PURPOSE: This study was to determine the role of changes in refractive error, contrast sensitivity, and corneal topography in transient changes in visual function following trabeculectomy. METHODS: We performed a prospective study evaluating these factors in 13 consecutive patients undergoing a standardized trabeculectomy. Preoperatively, and at 1, 4, and 12 weeks postoperatively, we measured best-corrected visual acuity, refractive error, and contrast sensitivity and analyzed computerized video-keratographic studies including estimated corneal visual acuity. RESULTS: One week postoperatively, best-corrected visual acuity decreased at least one line in 8 of 13 patients, whereas no eyes had decreased contrast sensitivity. Mean central corneal astigmatism increased 1.4 diopters along the surgical meridian. By 12 weeks, visual acuity returned to preoperative levels in all patients and the corneal topographic changes returned to within 1 diopter of preoperative values in 12 of 13 patients. Postoperative changes in estimated corneal visual acuity were similar to those in best-corrected visual acuity with no statistically significant difference. CONCLUSIONS: Corneal topographic changes appear to contribute to visual acuity reduction following trabeculectomy. In most cases this is transient with return to preoperative topography within 12 weeks.

Aged↗
PubMed1997

Retrospective comparison of techniques to prevent secondary cataract formation after posterior chamber intraocular lens implantation in infants and children.

PURPOSE: To determine the effect of various methods of managing the posterior capsule and anterior vitreous on the rate of posterior capsule opacification in pediatric eyes implanted with posterior chamber intraocular lenses (PC IOLs). SETTING: Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. METHODS: We reviewed the charts of 20 eyes of 15 children (aged 1.5 to 2 years) who had primary cataract surgery with PC IOL implantation during the past 5 years. The posterior capsule and anterior vitreous were managed in a variety of ways: In 5 eyes, the posterior capsule was left intact; in 15 eyes, a posterior continuous curvilinear capsulorhexis (PCCC) was performed - 6 with and 9 without anterior vitrectomy; in 8 eyes, posterior optic capture was performed - 3 with and 5 without vitrectomy. The follow-up ranged from 1 to 4.5 years (mean 2 years). RESULTS: Visually significant secondary cataract developed in the five eyes with intact posterior capsules and in the four eyes that had PCCC without vitrectomy and without posterior optic capture (i.e., the optic was left in the capsular bag). The optical axis remained clear in the six eyes that had PC IOL implantation with vitrectomy (with or without posterior optic capture). Initially, all eyes that had optic capture without vitrectomy also remained clear, but after 6 months, four of five developed opacification. CONCLUSION: In this series, PCCC with anterior vitrectomy was the only effective method of preventing or delaying secondary cataract formation in infants and children.

Cataract↗
PubMed1997

A retrospective comparison of techniques to prevent secondary cataract formation following posterior chamber intraocular lens implantation in infants and children.

PURPOSE: 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 posterior chamber intraocular lenses (PC IOL). METHODS: We reviewed the charts of 20 eyes of 15 children (1.5-12 years) who underwent primary cataract surgery with PC IOL in the last 5 years. The posterior capsule and anterior vitreous were managed in a variety of ways: in 5 eyes the posterior capsule was left intact, and 15 eyes underwent posterior continuous curvilinear capsulorhexis (PCCC)-nine cases without and 6 with anterior vitrectomy. In 8 eyes posterior optic capture was performed, 3 with and 5 without vitrectomy. The follow-up ranged from 1 to 4.5 years (mean: 2 years). RESULTS: Visually significant secondary cataract developed in all 5 eyes with intact posterior capsules and in the 4 eyes that underwent PCCC without vitrectomy and without posterior optic capture (i.e., the optic was left in the capsular bag). The optical axis remained clear in all 6 eyes that underwent PC IOL implantation with vitrectomy (with or without posterior optic capture). Initially, all optic capture cases without vitrectomy also remained clear, but after 6 months 4 out of 5 developed opacification. CONCLUSIONS: In this series posterior capsulorhexis with anterior vitrectomy was the only effective method of preventing or delaying secondary cataract formation in infants and children.

Capsulorhexis↗