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T Kohnen

Publications and source records attributed to T Kohnen.

At least 73 records · Page 4Linked to original sources
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

New caliper for small incision cataract surgery.

In cataract surgery, incision size determines various factors such as wound stability, corneal curvature changes, postoperative induced astigmatism, and visual rehabilitation. A mechanical caliper has been developed for experimental and clinical studies of incision sizes ranging between 1.0 and 6.0 mm. The caliper has a screw that allows measurements in 0.1 mm steps. The device is produced for two ranges: 2.0 to 4.0 mm and 1.0 to 6.0 mm. The precision of 0.1 mm was confirmed with a vernier caliper in a cadaver eye study. Unlike gauges that determine incision size by trial and error and a combined system of internal and vernier calipers, only one measurement is necessary with this caliper.

Astigmatism↗
PubMed1997

[Long-term outcome after implantation of various intraocular lenses through a corneal tunnel].

UNLABELLED: A prospective, randomized study was carried out to evaluate functional and biomicroscopic long-term results of different posterior chamber intraocular lenses (IOLs) over a period of two years after clear corneal cataract surgery. PATIENTS AND METHODS: 2 years after phacoemulsification through a temporal two-step clear corneal incision a total of 67 patients were examined. In 26 eyes (group A) a foldable plate-haptic silicone IOL (Chiron Adatomed, C10), in 25 eyes (group B) a foldable disc silicone IOL (Chiron Adatomed, 90D) had been implanted through a 3.5 (group A) or 4 mm (group B) corneal incision using a cartridge injector. In 16 eyes (group C) a one-piece PMMA-IOL (Pharmacia & Upjohn, 809C) had been implanted through a 5 mm incision. All eyes underwent functional and biomicroscopic examinations, as well as computerized videokeratographic analysis to obtain corneal topography data. RESULTS: In group A uncorrected visual acuity valued 0.64 (+/-0.29 SD), in group B 0.59 (+/-0.24) and in group C 0.56 (+/-0.27). Median of uncorrected visual acuity was 0.6 for all groups. Corrected visual acuity was 0.81 (+/-0.29) in group A, 0.8 (+/-0.25) in group B and 0.83 (+/-0.3) in group C. Intraocular pressure (mm Hg) was 13 (+/-2.5) in group A, 14.7 (+/-2) in group B and 15.1 (+/-2.5) in group C. Fibrosis of the anterior capsular rim occurred in 42% of the cases. One eye demonstrated folds in the posterior capsule (group B). Posterior capsular opacification valued 11.9% for all groups. In one eye a Nd:YAG-capsulotomy had already been performed. In group A a decentration of more than 1 mm was objected in one case, in group B in two cases and in group C in one case, but no patient complained about any functional impairment. Two years postoperatively, no signs of a re-flattening in the incision area could be detected using difference mapping tools in the videokeratographic analysis. CONCLUSION: Two years after implantation of foldable silicone IOLs and PMMA-IOLs via a temporal clear corneal tunnel incision after phacoemulsification only slight functional and morphologic differences between the three IOL-types could be observed.

Aged↗
PubMed1997

[Schnyder corneal dystrophy and juvenile, systemic hypercholesteremia].

BACKGROUND: Central crystalline dystrophy of Schnyder is characterized by the deposition of unesterified cholesterol crystals and lipids in the central and paracentral corneal stroma. Classically, this disease has been described as autosomal dominantly inherited and non-progressive with cholesterol deposits found in the anterior one third of the cornea. In recent years, however, rare sporadic cases and individuals with progressive, panstromal Schnyder's dystrophy have been described. Furthermore, an association has been made between some patients with Schnyder's dystrophy and a region on the coast in southwest Finland. Among the stromal dystrophies, this disease is unique with its occasional association with genu valgum and systemic hyperlipidemia. The role of high serum cholesterol in the pathogenesis of this disorder is still unclear. PATIENT: A ten-year-old white male presented with a one year history of ocular irritation made worse by bright sunlight. His past medical history was significant only for attention deficit disorder for which he received methylphenidate. A brother died at four months of age secondary to an unexplained cardiac abnormality. The ocular examinations of the patient's mother and father were normal and no history of eye disease among the grandparents could be elicited. The patient's visual acuity was 20/20 +2 in the right eye and 20/15 -3 in the left eye. The external examination showed no xanthelasmas. Slit-lamp biomicroscopy revealed bilateral ring-shaped corneal opacities extending into the midperiphery but sparing the limbal zone. The ring was composed of a fine, lacy garland of crystals present primarily in the anterior aspect of the stroma just beneath Bowman's membrane. The anterior chamber and iris showed no signs of inflammation. Intraocular pressures were 20 mm Hg and the ocular examination was otherwise unremarkable. Physical exam demonstrated no genu valgum. Blood testing showed a total cholesterol of 201 mg/dl with a low density lipoprotein cholesterol (LDL-C) of 156 mg/dl. Retesting four months later revealed a total cholesterol level of 245 mg/dl and an LDL-C of 192 mg/dl. The patient was referred to the pediatric gastroenterology service where he was put on diet therapy for further management of his hypercholesterolemia. CONCLUSIONS: This case appears to represent one of the rare sporadic examples of Schnyder's corneal dystrophy. The patient's family history is negative for ocular problems and the parents deny any Scandinavian ancestry. This patient is also unique for his presentation with ocular irritation. Most patients with Schnyder's dystrophy are initially seen for diagnosis of asymptomatic cloudy corneas or for gradual, painless loss of vision although glare in bright sunlight is noted by some individuals. Perhaps the most significant finding concerning this patient are his serum cholesterol levels. The association between total and LDL cholesterol and atherosclerotic vascular disease are well known and the literature suggests that regression of coronary artery disease is possible with aggressive treatment of hypercholesterolemia. Intervention in children should be considered if total cholesterol exceeds 170 mg/dl or LDL-C exceeds 110 mg/dl. Thus, early detection may eliminate significant morbidity and mortality. We therefore advocate evaluating all patients with Schnyder's corneal dystrophy and their immediate family members for systemic hypercholesterolemia.

Child↗
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↗
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

Comparison of viscoelastic substances used in phacoemulsification.

PURPOSE: To evaluate the usefulness of four viscoelastic agents during phacoemulsification: 2% hydroxypropylmethylcellulose (HPMC) (Methocel), 3% sodium hyaluronate with 4% chondroitin sulfate (Viscoat), 1% sodium hyaluronate (Healon), 1.4% sodium hyaluronate (Healon GV). SETTING: Eye Clinic, Kreiskrankenhaus Bad Hersfeld, Germany. METHODS: Two hundred patients, divided into four groups of 50 patients, received one of the viscoelastic substances during phacoemulsification and posterior chamber intraocular lens implantation. Patients were followed for 1 month. Visual acuity and intraocular pressure (IOP) were measured. The following were subjectively evaluated for each viscoelastic: corneal findings, anterior chamber reaction, visibility of intraocular structures and retention time during phacoemulsification, space maintaining ability, and removability and ease of injection. RESULTS: Postoperative IOP and visual acuity were comparable among the four groups. Viscoat tended to trap nuclear fragments and air bubbles during the phacoemulsification procedure, which decreased visibility during surgery. Space maintenance and injection ease were significantly better with Healon and Healon GV. CONCLUSION: The high molecular weight viscoelastics (Healon and Healon GV) performed better as viscosurgical tool during cataract surgery using phacoemulsification.

Chondroitin Sulfates↗
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↗