Biomedical subjects
B Seitz
Publications and source records attributed to B Seitz.
Lens opacities after nonmechanical versus mechanical corneal trephination for keratoplasty in keratoconus.
PURPOSE: To compare the lens opacity formation after penetrating keratoplasty (PKP) using nonmechanical excimer laser corneal trephination and mechanical motor trephination. SETTTING: University Eye Clinic, University of Erlangen-Nürnberg, Erlangen, Germany. METHODS: Ninety-six patients with keratoconus (96 eyes) and clear crystalline lenses were randomly assigned to the nonmechanical trephination (NMT) group (n = 46; 35 men; mean age 38.2 years +/- 10.8 [SD]) or the mechanical trephination (MT) group (n = 50; 35 men; mean age 34.4 +/- 9.0 years). Suturing and postoperative treatment were identical. Dilated pupil biomicroscopy and slitlamp lens photography were performed preoperatively and postoperatively at 3 month intervals. Opacities were identified as cortical, nuclear, and posterior subcapsular and graded from 1 (mild) to 3 (severe). RESULTS: Mean follow-up in the NMT/MT group was 3.2 +/- 1.3 years/3.4 +/- 1.1 years. Overall, incident opacities appeared in 23.9%/32.0% of eyes (4.3%/6.0% cortical; 19. 6%/26.0% posterior subcapsular; 0%/0% nuclear) (P =.833). All cortical opacities in both groups were grade 1; posterior subcapsular opacities were grade 1 in 66.6%/61.5% of eyes and grade 2 in 22.2%/30.8% of eyes. One patient in each group presented grade 3 posterior subcapsular opacities. No differences between trephination methods were seen in a 5 year Kaplan-Meier cumulative risk of lens opacity formation (P =.763 cortical, P =.530 posterior subcapsular). CONCLUSIONS: In addition to its optical advantages, nonmechanical corneal trephination appears to have no adverse impact on cataract formation after PKP for keratoconus.
Matrix polysaccharide precursors in Arabidopsis cell walls are synthesized by alternate pathways with organ-specific expression patterns.
The expression pattern of the single-copy gene UDP-glucose dehydrogenase (Ugd) was analysed in transgenic Arabidopsis plants by promoter:GUS and GFP fusions, Western blots, activity assays and histochemical activity staining. The enzyme oxidizes UDP-glucose to UDP-glucuronic acid and thus directs carbohydrates irreversibly into a cell wall-specific pool of nucleotide sugars. UDP-glucuronic acid is the central intermediate in the interconversion pathway to other nucleotide sugars, including the UDP-derivatives of arabinose, xylose, apiose and galacturonic acid which account for half the biomass of a typical Arabidopsis leaf cell wall. These activated sugars are needed as substrates for the biosynthesis of matrix polysaccharide polymers. In plants up to 5 days old the Ugd gene is strongly expressed in young roots, but very little in hypocotyls. Older plants show a more uniform expression pattern with a preference for the vascular system. A complex expression pattern was observed in flowers with high activity in the stamen, stigma and nectaries. Meristems in the leaf axil of rosette and inflorescence leaves exhibit a high level of activity of the Ugd gene. Although many of the growing tissues show high activity levels of the Ugd gene, others such as the hypocotyl and the cotyledons of young seedlings do not. Instead these tissues efficiently incorporate 3H-inositol into their cell walls. This indicates the biosynthesis of UDP-glucuronic acid through an alternative pathway via the oxidation of inositol to glucuronic acid and subsequent activation to the nucleotide sugar. The data strongly suggest two alternative pathways for matrix polysaccharide precursors with spatial and developmental regulation.
[Posterior corneal curvature after penetrating keratoplasty before and after suture removal].
PURPOSE: After penetrating keratoplasty (PK), peripheral swelling effects, malapposition of the graft in the recipient bed and suture tension may result in a changed ratio of curvature between anterior and posterior corneal surface. The purpose of this pilot study was to assess the posterior corneal curvature after PK with and without sutures and to compare this data to the posterior curvature of normal individuals. PATIENTS AND METHODS: In this cross-sectional study, 44 eyes after PK with a double running 16-bite diagonal antitorque suture in place (mean age 37 +/- 14 years, spherical equivalent (SEQ) -0.1 +/- 3.2 diopters (D)), 36 eyes with "all-sutures-out" (mean age 40 +/- 18 years, SEQ -0.8 +/- 3.5 D), and 464 normal control eyes (mean age 34 +/- 16 years, SEQ -0.3 +/- 2.2 D) were included. Based on Orbscan slit scanning topography analysis the following parameters were assessed: posterior power, posterior astigmatism, and posterior asphericity in various segments. RESULTS: With sutures in place the posterior central power ranged from -7.36 to -4.53 (mean -5.90 +/- 0.62) D, astigmatism ranged from 0.13 to 1.15 (mean 0.42 +/- 0.20) D, and asphericity ranged from 0.20 to 2.97 (mean 1.13 +/- 0.76, 56% oblate). With "all-sutures-out" the central power ranged from -7.56 to -4.93 (mean -6.41 +/- 0.53) D, astigmatism ranged from 0.13 to 1.15 (mean 0.39 +/- 0.19) D, and asphericity ranged from 0.26 to 3.04 (mean 1.25 +/- 0.76, 44% oblate). In the control group the central power ranged from -7.20 to -4.90 (mean -6.01 +/- 0.29) D, astigmatism ranged from 0.01 to 1.04 (mean 0.12 +/- 0.10) D, and asphericity ranged from 0.33 to 3.13 (mean 1.06 +/- 0.37, 47% oblate). Mean negative posterior power in grafts with "all-sutures-out" was significantly greater than in grafts with "all-sutures-in" and normal controls (p < 0.001), but showed no difference between the two latter groups (p = 0.56). Posterior astigmatism did not differ significantly comparing grafts with and without sutures (p = 0.44). However, astigmatism was significantly higher in grafts than in the control group (p < 0.0001). Asphericity did not differ significantly comparing grafts with and without sutures (p = 0.49) or comparing grafts to controls (p > 0.38). CONCLUSIONS: Except for the amount of astigmatism, the posterior corneal curvature of grafts with a double running suture in place does not seem to differ significantly from that of normal corneas. The removal of a double running suture tends to steepen the central posterior curvature. Knowledge about the individual posterior corneal curvature may have a favorable impact on the precision of intraocular lens power calculation for cataract surgery in eyes after PK.
[Decentration of donor cornea in mechanical and excimer laser trephination for penetrating keratoplasty].
BACKGROUND AND PURPOSE: Decentration of the trephination is supposed to be one of the major reasons for high and/or irregular astigmatism after penetrating keratoplasty (PK). The purpose of this study was to assess the amount and direction of donor decentration with conventional mechanical and nonmechanical laser trephination. PATIENTS AND METHODS: In this retrospective analysis 106 consecutive mechanical donor trephinations from the endothelial side (mean diameter 7.30 +/- 0.79 mm), 80 mechanical donor trephinations from the epithelial side (mean diameter 7.30 +/- 0.77 mm), and 89 nonmechanical donor trephinations from the epithelial side (Aesculap-Meditec; spot profile 1.5 x 1.5 mm, pulse energy 18-20 mJ, repetition rate 25/s) along metal aperture masks (mean diameter 7.72 +/- 0.40 mm) were included. Remaining corneoscleral rims were fixed in formalin after trephination and photographed from the endothelial side. On colour prints (13 x 18 cm; total magnification x7.33) the amount and direction of decentration were assessed morphometrically using the SummaSketch (Summagraphics, Seymour, USA) and correlated with the total area of the cornea and the trephination. RESULTS: Mean donor decentration was significantly smaller with laser trephination (0.20 +/- 0.12 mm) than with mechanical trephination from the endothelial side (0.26 +/- 0.14 mm; p = 0.001) and from the epithelial side (0.27 +/- 0.16 mm; p = 0.024). In addition, donor decentration correlated significantly inversely with the trephination area (p < 0.001), but not with the total area of the cornea (p = 0.63). A preferred direction of decentration relative to the microsurgeon could not be detected (p = 0.87). CONCLUSIONS: Centration of donor trephination can be improved by using nonmechanical instead of mechanical trephination of the cornea. Further studies are required to investigate the clinical relevance of the statistically better donor centration on astigmatism and visual acuity after PK.
[Corneal dimensions in various types of corneal dystrophies and their effect on penetrating keratoplasty].
PURPOSE: To achieve a high optical performance and a low rate of immunologic graft reactions after penetrating keratoplasty (PK) an optimal graft outline has to be chosen. The purpose of this study was to compare the corneal dimensions of patients with various types of corneal dystrophies to normal control eyes. METHODS: In patients with keratoconus (n = 117), Fuchs' (n = 100), granular (n = 28), lattice (n = 26) and macular corneal dystrophy (n = 25) and normal controls subjects (n = 93) standardized slit lamp photographs of the cornea were taken. Using a computerized planimeter (SummaSketch III, Summagraphics Corp., Seymour, USA) 13 x 18-cm color prints (total magnification x12) were assessed morphometrically. RESULTS: On average, the maximal and the minimal diameter of corneas in patients with macular dystrophy (12.3 mm/10.6 mm) and normal controls (12.1 mm/10.5 mm) were significantly smaller (p < 0.02) than in patients with keratoconus (12.6 mm/10.9 mm), granular (12.7 mm/10.8 mm) and lattice dystrophy (12.8 mm/10.8 mm), but significantly larger (p < 0.02) than in patients with Fuchs' dystrophy (11.9 mm/10.4 mm). In Fuchs' dystrophy the corneas were significantly (p < 0.0001) more elliptical than in all other dystrophies and controls. The rotation of the maximal diameter from the horizontal ranged from 36 degrees nasal inferior to 44 degrees nasal superior and did not differ between dystrophies and controls. CONCLUSIONS: In patients with keratoconus, lattice and granular dystrophy larger grafts may be considered to improve the optical performance without promoting the risk of immunologic graft reactions after PK. As a rule, we use 8.0/8.1 mm (recipient/donor) for keratoconus and 7.5/7.6 mm for Fuchs' dystrophy. However, the graft diameter has to be determined individually in each single eye immediately before trephination.
[Interim results from the prospective "Erlanger Non-high-risk Penetrating Keratoplasty Study" in 207 patients].
BACKGROUND: Immunologic graft rejection targeted against corneal endothelium is the most frequent cause for graft failure after corneal transplantation. The purpose of this prospective study was to assess the frequency, early symptoms, prophylaxis and therapy monitoring of corneal graft rejection following non-high-risk penetrating keratoplasty (PK). PATIENTS AND METHODS: From February 1997 to May 1999, 237 patients undergoing non-high-risk PK have been enrolled in this prospective study. We evaluated 207 patients (103 female, 113 right eyes, recipient age 54 +/- 20 years, donor age 59 +/- 17 years). In 2 randomized treatment studies we compared the efficacy of postoperative short-term (ST = 6 months) versus long-term (LT = 12 months) topical steroid therapy on the incidence of graft rejection and the effect of high- versus low-dose systemic steroid therapy on the prognosis after a graft rejection. Follow-up examinations included, laser-tyndallometry, corneal topography analysis, endothelial cell count and pachymetry. RESULTS: The main indications for PK were keratoconus (n = 93), endothelial dystrophy Fuchs (n = 52) and bullous keratopathy (n = 35). In 151 (73%) patients, non mechanical trephination with the 193 nm Excimer laser was performed. Up to now, 78 patients were randomized into two groups comparing the postoperative therapy with topical steroids. During follow-up (median: ST: 13.5 months; LT: 12.5 months, maximum 25.3 months) episodes of endothelial graft rejection (3 chronic focal, 8 acute diffuse) showed 11 eyes of 11 patients. Five patients each had short-term and long-term topical steroid treatment. In 1 patient the graft rejection occurred before randomization at 6 months. Six patients with graft rejection episodes underwent a PK only (54% of graft rejections, 4.4% of all patients). In the remaining 5 patients, PK was combined with a lens surgery (46% of graft rejections, 6.9% of all patients). Ten of 11 corneal grafts regained their full function under treatment with systemic and local steroids. CONCLUSION: The frequency of episodes of graft rejection in our study was lower than usually reported in the literature. A good compliance of patients appears to be a major factor for improved prognosis of the graft after PK and in case of graft rejection. Until now no significant differences between short-term or long-term postoperative topical steroid therapy could be detected regarding the incidence of corneal graft rejection.
[Frequency and risk factors of intraocular pressure increase after penetrating keratoplasty].
PURPOSE: The aim of this study was to evaluate the incidence, risk factors and management of glaucoma following penetrating keratoplasty (PK) and to check for possible correlations with the indication for PK. PATIENTS AND METHODS: 534 eyes of 483 patients (age 54.7 +/- 19.8 years), that had undergone PK from 1989 to 1999 were retrospectively analyzed. The mean follow-up was 2.7 +/- 1.8 years. According to the type of surgical procedure patients were classified in 5 groups: group 1) PK only (n = 291); group 2) PK combined with extracapsular cataract extraction and intraocular lens (IOL) implantation (n = 124); group 3) PK combined with secundary IOL-implantation or IOL-change (n = 32); group 4) PK only after previous cataract surgery (n = 55) and group 5) Cataract surgery after PK (n = 32). The trephination was performed from the epithelial side in donor and recipient either by nonmechanical trephination with the 193 nm excimer laser (n = 444) or mechanical trephination (n = 90). An iridotomy was performed routinely during PK. The postoperative treatment with topical steroids was standardized. RESULTS: Preoperatively, glaucoma was diagnosed in 3.2% for all patients with groups 3 und 4 showing a significantly larger number of glaucomatous eyes (15.6% and 18.9%). Most of the mild early intraocular pressure elevations in group 1 (3.4%) and group 2 (3.0%) were controlled after 6 months (0.5% and 1.1%). Groups 3 and 4 showed most frequently increased intraocular pressure and/or antiglaucomatous treatment (21.4% and 18.7%) six weeks postoperatively. Patients in all groups showed no higher prevalence of persistent glaucoma from six months postoperatively than preoperatively throughout the follow-up period. Again groups 3 and 4 presented the largest number of persistent glaucoma. In most eyes the IOP was controlled by topical antiglaucomatous treatment. Serious forms seen in 2 patients with anterior synechiae caused by anterior chamber lens required several filtering surgeries or pars plicata diathermy, respectively. One patient with pseudoexfoliation syndrome required laser trabeculoplasty. The so-called "Urrets-Zavalia syndrome" was seen in none of the patients. CONCLUSION: The development of increased intraocular pressure after PK varied with the indication for keratoplasty. Postkeratoplasty glaucoma seems to be strongly associated with preexisting anterior synechiae and/or simultaneous anterior chamber lens implant removal. Intraoperative iridotomy can prevent the development of acute angle closure glaucoma after keratoplasty.
[Regression analysis of corneal endothelium after nonmechanical penetrating keratoplasty].
PURPOSE: The corneal endothelial cell density is a crucial parameter for the pump function and the transparency of grafts after penetrating keratoplasty (PK). The purpose of this study was to assess corneal endothelial cell density with different regression models after nonmechanical penetrating keratoplasty and to check for differences between diagnoses and two different storage methods. PATIENTS AND METHODS: Two-hundred ninety-six eyes (195 keratoconus, 101 Fuchs' dystrophies, 148 each with short-term preserved and organ-cultured donor corneas) of 268 patients were included in this prospective study. Donor and recipient trephination was performed using nonmechanical trephination technique with the excimer laser 193 nm along metal aperture masks from the epithelial side. The time course of the endothelial cell density (specular microscope EM 1100, TOMEY, Erlangen) after PK was assessed. Endothelial cell density was first analyzed in a cross sectional manner at the 3, 6, 12, 18 and 24 months follow-up and, secondly in a longitudinal manner with linear, polynomial and exponential regression models in the sense of minimizing the residuum (distance between observed and predicted endothelial cell count). The mean donor postmortem time was 10.3 +/- 6.8 hours for short-term-preserved and 19.6 +/- 9.5 hours for organ-cultured corneas (p < 0.0001). The storage time was 63 +/- 49 and 19 +/- 7 days (p < 0.0001), respectively. RESULTS: In a cross section, overall mean endothelial cell density decreased from 2145 +/- 599 cells/mm2 at the 3 months to 1751 +/- 605 cells/mm2 at 2 years follow-up (p > 0.05). Cell density did not differ significantly between different diagnoses or storage methods at any postoperative stage. In a longitudinal section, the linear regression model estimated an annual decrease of 214 cells/mm2. In a polynomial model the decrease expressed by a tangent to the regression line at 24 months was 175 cells/mm2. The exponential regression model yielded a relative decrease of 9.5% annually. The so-called residuum as a measure for the validity of the regression model was maximal in the linear and minimal in the exponential estimate. With keratoconus and short-term preserved donor material the endothelial cell loss was less in the regression analysis. CONCLUSION: During the first two years after nonmechanical trephination in PK, a non-significant decrease in endothelial cell density was observed. The exponential regression model seems to be predestinated for analysis of the time course of corneal endothelium in a longitudinal manner. The annual cell loss ranged around 9.5% without significant differences between diagnoses and storage methods.
Intraocular lens calculations status after corneal refractive surgery.
With the increasing number of keratorefractive surgical procedures, an increasing number of cataract surgeries in eyes after keratorefractive surgery is anticipated within a few decades. Although cataract extraction seems to be feasible without major technical obstacles, intraocular lens (IOL) power calculation turned out to be problematic. Insertion of the measured average K-readings (= "central corneal power" = keratometric diopters) after myopic radial keratotomy (RK), photorefractive keratectomy (PRK), or laser in situ keratomileusis (LASIK) into standard IOL power-predictive formulas commonly results in substantial undercorrection and postoperative hyperopic refraction or anisometropia. In this article, the major reasons for IOL power miscalculations (which are different for RK versus RRK/LASIK) are discussed based on model calculations and based on case series of cataract surgeries, methods for improved assessment of keratometric diopters as the major underlying problem are exemplary illustrated, and finally a clinical step-by-step approach to minimize IOL power miscalculations status after corneal refractive surgery is suggested. The "clinical history method" (i.e., subtraction of the spherical equivalent [SEQ] change after refractive surgery from the original K-reading) should be applied whenever refraction and K-reading before the keratorefractive procedure are available to cataract surgeons. In addition, more than one modern third-generation formula (e.g., Haigis, Hoffer Q, Holladay 2, or SRK/T) but not a regression formula (e.g., SRK I or SRK II) should be applied and the highest resulting IOL power should be used for the implant.
The linear plasmid SCP1 of Streptomyces coelicolor A3(2) possesses a centrally located replication origin and shows significant homology to the transposon Tn4811.
The linear plasmid SCP1 of Streptomyces coelicolor A3(2) is one of the genetically more studied linear streptomycete replicons. Although the genetics of SCP1 and its interaction with the host chromosome have been analyzed for nearly three decades no information exists on its replication. With the help of an ordered cosmid contig for the complete 360-kb element, we have localized a 5439-bp fragment from the central region that confers autonomous replication in Streptomyces lividans. The minimal origin contains two overlapping ORFs which are separated from an AT-rich region which might correspond to the replication start point. ORF1 revealed intensive similarity to a class of DNA-primase/helicases of actinophages and archael plasmids. In addition, we have identified a region in both terminal inverted repeats of SCP1 that shows significant homology to the transposable element Tn4811 located near the ends of the S. lividans 66 chromosome.
Influence of soil storage and exposure period on DNA recovery from teeth.
A study was performed to determine the influence of garden soil on the deoxyribonucleic acid (DNA) recovery from teeth depending on the duration of storage. In the first series 24 teeth supplied by dentists were exposed to garden soil storage for a maximum of 18 weeks. Selected samples were excavated for DNA extraction at time intervals of 6, 12 and 18 weeks. For the second series 20 teeth were stored for one year in garden soil. Following phenol/chloroform extraction with decalcification (first series) and without decalcification prior to extraction (second series) DNA was quantified, amplified using the polymerase chain reaction (PCR) for the tandem repeat loci D1S80, tyrosine hydroxylase, intron 1 (TH01) and Von Willebrand factor, intron A (VWA) (first series), human alpha fibrinogen (FGA) (second series) and sequenced in the hypervariable regions 1 and 2 (HV1, HV2) of the mitochondrial DNA (second series). The DNA concentration of the extracts after the first 6 weeks in soil was reduced by more than 90%. Amplification and direct sequencing of HV1 and HV2 of the mitochondrial genome was the most successful DNA technique.
Quantification of blood-aqueous barrier breakdown after photorefractive keratectomy for myopia.
BACKGROUND: Photorefractive keratectomy (PRK) using the excimer laser is a well-established surgical technique for correction of mild to moderate myopic refraction errors in case of spectacle or contact lens incompatibility. As it is still uncertain whether this procedure causes intraocular inflammatory changes, it was the purpose of this study to quantify breakdown of the blood-aqueous barrier following PRK and to look for possible correlations with clinical parameters. PATIENTS AND METHODS: Aqueous flare was quantified using the laser flare-cell meter after medical pupil dilation preoperatively and on days 1, 3 and 7 as well as 1 month and 3 months following PRK with a 193-nm excimer laser (MEL 60, Aesculap-Meditec) in 37 eyes of 22 patients. The preoperative spherical equivalents were -4.4 +/- 3.1 D (range -1.5 to -8.0 D). Pre-, intra- and postoperative treatment was standardized. RESULTS: Preoperatively, aqueous flare values were 3.9 +/- 0.8 photon counts/ms and showed no significant correlation with the spherical equivalent (p > 0.1). Postoperatively, aqueous flare rise was very small with flare values not significantly higher than preoperative values. All postoperative flare values were below the normal limit (< 8.0 photon counts/ms). Flare was highest on day 3 after PRK surgery. There was no statistically significant correlation between aqueous flare and depth of stromal ablation. The number of aqueous "cells" did not increase following PRK at any postoperative follow-up examination. CONCLUSION: Our results indicate that PRK in mild to moderate myopia does not cause a significant breakdown of the blood-aqueous barrier.
Free-running erbium:YAG laser for nonmechanical trephination in penetrating keratoplasty: first results of experimental trephination of human donor corneas.
BACKGROUND: A study was carried out to evaluate the potential suitability of a free-running erbium:YAG 2.94-microm laser for trephination of human corneas in penetrating keratoplasty. METHODS: Two human donor corneas were placed in an artificial anterior chamber and moved with an automated rotation device (one rotation per minute). An erbium:YAG laser beam (pulse duration 400 micros, repetition rate 2/s, energy density 2.5 and 15.0 J/cm(2)) was focused on the outer edge of a round ceramic mask placed on the human donor corneas for ablation of tissue. RESULTS: With a fluence of 15.0 J/cm(2), perforation was achieved after 500 pulses. Perpendicular central cut edges with mild stromal ridges and, by light microscopy, a 12 to 45-microm area of stromal thermal effects and focal endothelial changes up to 200 microm central to trephination were observed. CONCLUSIONS: The erbium:YAG laser could be a promising "low-cost alternative" to the excimer laser for nonmechanical trephination in penetrating keratoplasty. Further studies will have to focus on reduction of thermal damage and on wound healing.
Endothelium and pachymetry of clear corneal grafts 15 to 33 years after penetrating keratoplasty.
PURPOSE: To evaluate long-term endothelial cell count and thickness of clear corneal grafts after penetrating keratoplasty. METHODS: Specular microscopy and ultrasonic pachymetry were performed in 20 eyes (14 eyes that were keratoconus, three aphakic/pseudophakic bullous keratopathy, one Fuchs dystrophy, one had herpetic keratitis, and one avascular scar after injury) of 18 patients (mean age +/- SD 58+/-15 years; range, 34 to 82 years) with a mean follow-up of 22+/-6 years (range, 15 to 33 years). RESULTS: Mean endothelial cell count was 808+/-194 cells per mm2 (range, 575 to 1243 cells/mm2), and thickness was 608+/-75 microm (range, 430 to 751 microm). Endothelial cell count was neither correlated with thickness (P = .25, r2 = .08) nor with follow-up interval (P = .31, r2 = .028). We observed predominantly enlarged endothelial cells and mild polymegethism. No graft rejections were recorded. CONCLUSION: Despite a reduced cell density, the dehydration function of the endothelium may still be sufficient in corneal grafts up to 33 years after penetrating keratoplasty.
Underestimation of intraocular lens power for cataract surgery after myopic photorefractive keratectomy.
OBJECTIVE: To assess the validity of corneal power measurement and standard intraocular lens power (IOLP) calculation after photorefractive keratectomy (PRK). DESIGN: Nonrandomized, prospective, cross-sectional, clinical study. PARTICIPANTS: A total of 31 eyes of 21 females and 10 males with a mean age at the time of surgery of 32.3 +/- 6.6 years (range, 24.4-49.5 years). INTERVENTION: Subjective refractometry, standard keratometry, TMS-1 corneal topography analysis, and pachymetry were performed before and 15.8 +/- 10.4 months after PRK for myopia (n = 24, -1 .5 to -8.0 diopters [D], mean -5.4 +/- 1.9 D) or myopic astigmatism (n = 7, sphere -2.0 to -7.5 D, mean -4.4 +/- 1.9 D; cylinder -1.0 to -3.0 D, mean -1.9 +/- 0.7 D). The IOLP calculations were done using two different formulas (SRK/T and HAIGIS). MAIN OUTCOME MEASURES: Keratometric power (K) and topographic simulated keratometric power (TOPO) as measured (Kmeas, TOPOmeas) and as calculated according to the change of power of the anterior corneal surface or according to the spherical equivalent change after PRK (Kcalc, TOPOcalc), IOLP for emmetropia, and postoperative ametropia for calculated corneal powers were assessed in a model. RESULTS: After PRK, mean Kmeas and TOPOmeas were significantly greater (0.4-1.4 D, maximum 3.3 D) than mean KRcalc and TOPOcalc (P < 0.0001). On average, the relative flattening of the cornea after PRK was underestimated by 14% to 30% (maximum, 83%) depending on the method of calculation. The mean theoretical IOLP after PRK ranged from + 17.4 D (SRK/T, TOPOmeas) to +20.9 D (HAIGIS, Kcalc) depending on the calculation method for corneal power and IOLP calculation formula used. For both formulas, IOLP values using keratometric readings were significantly higher (>1 D) than IOLP values using topographic readings (P < 0.0001). The theoretically induced mean refractive error after cataract surgery ranged from +0.4 to +1.4 (maximum, +3.1) D. Corneal power overestimation and IOLP underestimation correlated significantly with the spherical equivalent change after PRK (P = 0.001) and the intended ablation depth during PRK (P = 0.004). CONCLUSIONS: To avoid underestimation of IOLP and hyperopia after cataract surgery following PRK, measured corneal power values must be corrected. The calculation method using spherical equivalent change of refraction at the corneal plane seems to be the most appropriate method. In comparison with this method, direct power measurements underestimate corneal flattening after PRK by 24% on average. Use of conventional topography analysis seems to increase the risk of error. However, because this study is retrospective and theoretical, there is still a need for a large prospective investigation to validate the authors' findings.
Nonmechanical corneal trephination with the excimer laser improves outcome after penetrating keratoplasty.
OBJECTIVE: To assess the impact of nonmechanical trephination on the outcome after penetrating keratoplasty (PK). DESIGN: Prospective, randomized, cross-sectional, clinical, single-center study. PATIENTS: A total of 179 eyes of 76 females and 103 males, mean age at the time of surgery 50.6 +/- 18.5 (range, 15-83) years. Inclusion criteria were (1) time interval from October 1992 to December 1997; (2) one surgeon (GOHN); (3) primary central PK; (4) Fuchs dystrophy (diameter, 7.5 mm) or keratoconus (diameter, 8.0 mm); (5) graft oversize, 0.1 mm; (6) no previous intraocular surgery; and (7) 16-bite double-running diagonal suture. INTERVENTION: In a randomized fashion, eyes were assigned either to trephination with the 193-nm Meditec excimer laser (manually guided beam in patients, automated rotation device of artificial anterior chamber in donors) along metal masks with eight orientation teeth/notches (EXCIMER: 53 keratoconus, 35 Fuchs dystrophy; mean follow-up, 37 +/- 16 months) or with a hand-held motor trephine (Microkeratron; Geuder) ( CONTROL: 53 keratoconus, 38 Fuchs dystrophy; mean follow-up, 38 +/- 14 months). Subjective refractometry (trial glasses), standard keratometry (Zeiss), and corneal topography analysis (TMS-1; Tomey) were performed before surgery, before removal of the first suture (15.2 +/- 4.2 months), and after removal of the second suture (21.4 +/- 5.6 months). MAIN OUTCOME MEASURES: Keratometric and topographic net astigmatism as well as refractive cylinder; keratometric and topographic central power; best-corrected visual acuity (VA); surface regularity index (SRI), surface asymmetry index (SAI), and potential visual acuity (PVA) of the TMS-1. RESULTS: Before suture removal, mean refractive/keratometric/topographic astigmatism did not differ significantly between EXCIMER (2.5 +/- 1.8 diopters [D]/3.4 +/- 2.8 D/4.7 +/- 3.1 D) and CONTROL groups (3.0 +/- 1.8 D/3.7 +/- 2.4 D/4.3 +/- 2.1 D). After suture removal, respective values were significantly lower in the EXCIMER group (2.8 +/- 2.0 D/3.0 +/- 2.1 D/3.8 +/- 2.6 D) than in the CONTROL group (4.2 +/- 2.4 D/6.1 +/- 2.7 D/6.7 +/- 3.1 D) (P < 0.0009). In the EXCIMER versus CONTROL group, mean VA increased from 20/100 versus 20/111 (P > 0.05) before surgery, to 20/31 versus 20/38 before (P = 0.001) and to 20/28 versus 20/39 (P < 0.00001) after suture removal. Mean spherical equivalent was significantly less myopic in the EXCIMER group before (-0.9 +/- 3.6 D vs. -2.6 +/- 3.4 D) (P = 0.01) and after suture removal (-1.4 +/- 3.1 D vs. -2.4 +/- 3.5 D) (P = 0.02). Mean SRI (P = 0.04) and PVA (P = 0.007) were significantly more favorable in the EXCIMER versus CONTROL group after suture removal (0.91 +/- 0.45 and 0.82 +/- 0.15 vs. 1.05 +/- 0.46 and 0.73 +/- 0.18). CONCLUSIONS: Postkeratoplasty results seem to be superior using nonmechanical excimer laser trephination. Thus, this methodology is recommended as the procedure of first choice in avascular corneal pathologies requiring PK.
Nonmechanical excimer laser penetrating keratoplasty for perforated or predescemetal corneal ulcers.
OBJECTIVE: To review the authors' results using nonmechanical excimer laser trephination in penetrating keratoplasty for perforated or predescemetal corneal ulcers. DESIGN: Noncomparative, consecutive, interventional case series. PARTICIPANTS: Thirty-two patients with perforated (17) or deep (15) corneal ulcers (9 bacterial, 5 acanthamoebal, 10 herpetic, 3 associated with rheumatoid arthritis, 5 other) necessitating immediate tectonic keratoplasty. INTERVENTION: Penetrating tectonic keratoplasty with excimer laser trephination was performed along metal aperture masks in donor and recipient corneas. MAIN OUTCOME MEASURES: Clinical results including intraoperative and postoperative complications were evaluated. RESULTS: Trephination was possible in all eyes without perforation of predescemetal ulcers or extrusion of intraocular contents. No eyes with bacterial or acanthamoebal ulcers showed persistence or recurrence of infection. One eye showed recurrent epithelial herpetic keratitis. Best-corrected postoperative visual acuity ranged from 20/700 to 20/20 (median, 20/58), with 30 of 32 eyes achieving improvement of best visual acuity during follow-up (mean, 22.4 months) and with 12 of 32 eyes reaching a visual acuity of 20/40 or greater. Eyes with bacterial or acanthamoebal ulcers showed best results. Episodes of graft rejection occurred in nine eyes and resulted in irreversible opacity of the graft in seven cases. None of the eyes lost all vision, developed endophthalmitis, or had to be enucleated. CONCLUSIONS: Nonmechanical trephination is a useful technical refinement of tectonic penetrating keratoplasty à chaud for perforated or deep progressive corneal ulcers. This technique greatly facilitates exact trephination under these difficult surgical conditions and might possibly improve the prognosis of this procedure.