Biomedical subjects

M M Kus

Publications and source records attributed to M M Kus.

At least 19 recordsLinked to original sources

PubMed2004

[Results of the first 1,000 consecutive elective nonmechanical keratoplasties using the excimer laser. A prospective study over more than 12 years].

BACKGROUND AND PURPOSE: The purpose of this prospective clinical cross-sectional study was to analyse indications, intraoperative, perioperative and postoperative pecularities and complications as well as postoperative functional and morphologic results of the first 1000 consecutive elective round laser keratoplasties. PATIENTS AND METHODS: The age of the 480 females and 520 males (362 x keratoconus), who had been operated on between 07/1989 and 04/2002 ranged from 20 to 92 years (mean 55+/-19). A total of 6 microsurgeons performed 718 x PK only, 222 x a triple procedure and 60 x additional IOL manoeuvres. Recipient and donor trephinations were accomplished with an 193 nm excimer laser (Carl Zeiss Meditec, Jena, Germany) from the epithelial side. RESULTS: In 895 eyes with perioperative corneal erosion, epithelial healing took not more than 3 days in half of cases. During a follow-up period of 1.9+/-1.5 years, in 35 eyes episodes of acute diffuse (8 irreversible) and in 12 eyes episodes of chronic focal (5 irreversible) endothelial immunologic graft reactions (4.7%) occurred between 6 weeks and 4.7 years after PK. Before/after suture removal, median values of astigmatism were 1.5 diopters (D)/2.5 D refractive, 3.0 D/3.3 D keratometric, and 4.0 D/4.2 D topographic. Best-corrected visual acuity was 0.50/0.60, respectively. CONCLUSIONS: More than 12 years of experience with this new technique indicate that besides optical advantages, nonmechanical trephination does not cause intraoperative or postoperative disadvantages for the patient. Under standardised surgical conditions a massive increase of astigmatism after suture removal seems to be avoidable with laser trephination in most cases due to reduction of decentration,"vertical tilt" and especially "horizontal torsion".

Adult↗

PubMed2002

[Phototherapeutic keratectomy for recurrent corneal erosion syndrome (e-PTK). Report on 116 consecutive interventions].

BACKGROUND AND AIMS: Patients with recurrent corneal erosion syndrome can suffer both psychologically and socially due to excessive pain. After the failure of conservative treatment, conventional surgical interventions, such as anterior stromal puncture have been suggested. The purpose of this study was to assess the morphological and functional results of minimally invasive excimer laser phototherapeutic keratectomy (e-PTK) for treatment of recurrent corneal erosion syndrome and in particular, to evaluate the cumulative recurrence rate. PATIENTS AND METHODS: Between July 1990 and January 2001, 116 e-PTKs have been performed mostly in the acute stage of the disease in this single center study. In 15 eyes an unsuccessful PTK had previously been performed elsewhere. Reasons for the erosion included trauma ( n=80), Cogan's epithelial dystrophy ( n=14), bullous keratopathy ( n=2), and in 20 cases no cause could be detected. A manually guided spot profile was applied in 99 cases (pulse energy 10 mJ, repetition rate 2/s or 3/s, 66-330 pulses). In 17 cases a scanning slit procedure was applied (intended ablation per scan 1 microm, repetition rate 20/s, 447-1,017 pulses). The broad deepithelialisation of Bowman's layer was treated with defocussed overlapping laser pulses. RESULTS: Complete epithelial closure was achieved after an average of 2.3+/-1.3 (median 2) days, the mean follow-up was 2.2+/-1.6 years with a maximum of 5.6 years. Best corrected visual acuity increased from 0.6+/-0.4 preoperatively to 0.9+/-0.3 postoperatively. The keratometric central power remained constant (preoperative 43.0+/-2.2 D (diopters), postoperative 43.3+/-1.9 D). The median keratometric astigmatism remained constant at 1.0 D. Only in 2 patients was an iatrogenic, not completely reversible irregular astigmatism of more than 2 D induced during the learning curve. The spherical equivalent did not change significantly (-1.0+/-3.3 D preop., -1.1+/-3.4 D postop.). In 9 eyes (7.8%) a recurrent epithelial defect occurred after 2-24 (average 8+/-6) months. The cumulative 1-year recurrence rate was 6.5%, the 2-year recurrence rate was 11.5%, the 3-, 4-, and 5-year recurrence rates were all 13.6%. CONCLUSIONS: For recurrent corneal erosion syndrome, e-PTK performed with low pulse energy and low number of pulses can be considered an effective treatment modality to achieve a fast and mostly durable epithelial closure. Even after broad removal of the loose epithelium, change of refraction or induction of an irregular astigmatism with visual loss seems to be the exception.

Adult↗

PubMed2001

Graft endothelium and thickness after penetrating keratoplasty, comparing mechanical and excimer laser trephination: a prospective randomised study.

PURPOSE: To assess the impact of nonmechanical trephination on the graft endothelium and thickness after penetrating keratoplasty (PK). METHODS: Inclusion criteria for this prospective, randomised, cross-sectional, clinical study were: (1) Treatment between October 1992 and December 1997; (2) one surgeon (G.O.H.N.); (3) primary central PK; (4) Fuchs' dystrophy (diameter 7.5/7.6 mm) or keratoconus (diameter 8.0/8.1 mm); (5) graft oversize 0.1 mm; (6) no previous intraocular surgery; (7) 16-bite double-running diagonal suture. In 179 patients (mean age 51+/-18 years), PK was performed using either the 193-nm Meditec MEL60 excimer laser ("Excimer") along metal masks with eight "orientation teeth/notches" (53 keratoconus, 35 Fuchs' dystrophy) or motor trephination with the Mikrokeratron (Geuder) ("Control": 53 keratoconus, 38 Fuchs' dystrophy). For donor trephination from the epithelial side an artificial anterior chamber was used in both groups. In 27% of the excimer and 29% of the control group a triple procedure was performed. Specular microscopy (EM-1000, Tomey) and pachymetry (SP-2000, Tomey) were performed before removal of the first suture (0.4+/-0.2 years postoperatively), before (1.1+/-0.4 years) and after (1.7+/-0.6 years) removal of the second suture but before any additional surgical intervention. RESULTS: Endothelial cell count: Neither "two-sutures-in" (1953+/-426/1804+/-385 cells/mm2, p=0.13), "one-suture-in" (1629+/-439/1765+/-440 cells/mm2, p=0.27), nor "all-sutures-out" (1259+/-493/1294+/-532 cells/mm2, p=0.83) differed significantly between Excimer and Control. Graft thickness: Neither "two-sutures-in" (527+/-58/524+/-16 mucrom, p=0.89), "one-suture-in" (537+/-72/551+/-40 microm, p=0.86), nor "all-sutures-out" (576+/-53/565+/-62 microm, p=0.38) differed significantly between Excimer and Control. Cell count and corneal thickness were not significantly different comparing Fuchs' dystrophy and keratoconus or comparing PK only and triple procedures. Graft thickness and endothelial cell count correlated highly significantly inversely with "all sutures out" (P<0.0001). CONCLUSIONS: Excimer laser trephination from the epithelial side using an artificial anterior chamber in donors seems to have no disadvantages concerning the graft endothelium after PK. Endothelial cell loss was not increased in eyes with Fuchs' dystrophy compared with keratoconus or after triple procedures compared with PK only.

Adolescent↗

PubMed2001

[Impact of pterygium size on corneal topography and visual acuity - a prospective clinical cross-sectional study].

PURPOSE: Pterygia may cause topographic changes featuring increase of astigmatism. The purpose of this study was to quantify the impact of the head-limbus-distance (=height) and limbal base length of the pterygium on the anterior corneal curvature and visual acuity before excision. PATIENTS AND METHODS: In 52 eyes (19 female, 33 male) with a mean age of 53 +/- 14 years the pterygium size (height, base length, area) was quantified using projected preoperative clinical slides and was correlated with visual acuity, refractive, keratometric, topographic astigmatism and Surface Regularity Index (SRI), Surface Asymmetry Index (SAI) of the TMS-1 videokeratoscope. RESULTS: The mean height of the pterygium was 3.1 +/- 1.4 (0.8 to 6.7) mm, the mean base length was 5.1 +/- 1.4 (2.9 to 7.8) mm, the estimated mean area was 11.4 +/- 6.9 (2.1 to 29.4) mm(2). The increasing pterygium height and area resulted in a highly significant elevation of the preoperative SRI and SAI values (p </= 0.01). The amount of keratometric (p=0.02) and topographic astigmatism (p=0.001) correlated significantly with height and area of the pterygium. In addition, pterygium size correlated significantly with the differences of zonal corneal power between steepest and flattest hemimeridian in the 3-mm zone or 5-mm zone, respectively (p </= 0.01). Best-corrected visual acuity and height/area of the pterygium correlated significantly inversely (p=0.001). Visual acuity seemed to be mostly unaffected up to a height of 2.5 mm. Overall, the impact of the base length was much less striking. Topographic astigmatism (3.3 +/- 2.8 D) was significantly larger than keratometric astigmatism (2.1 +/- 2.1 D) (p=0.001). The larger the pterygium, the larger was the difference between keratometric astigmatism and subjectively tolerated spectacle cylinder (p </= 0.01). CONCLUSIONS: Increasing distance of the pterygium head from the limbus results in increased amount and irregularity of preoperatively induced corneal astigmatism. This may explain the patient's decrease in visual acuity before the pterygium reaches the optical axis. Our data may help to determine the adequate time point for primary pterygium excision.

Adult↗

PubMed2000

Thermal load of laser aperture masks in nonmechanical trephination for penetrating keratoplasty with the Er:YAG laser: comparison between stainless steel and ceramic masks.

PURPOSE: Thermal effects on the laser aperture mask may play a major role in the thermal loading of the cornea during nonmechanical trephination in penetrating keratoplasty. The purpose of this study was to assess the temperature increase on the laser mask using the 2.94-microm Er:YAG laser in order to find suitable parameters for avoidance of thermal damage to the cornea. METHODS: Thermal load measurements were performed on donor (7.5 mm trephination diameter, 0.7 mm thickness, central hole 3.0 mm) and recipient (7.5 mm trephination diameter, 0.7 mm thickness, outer diameter 13.0 mm) aperture masks. The masks were either mounted on a thermal isolator or fixed directly on porcine corneal samples. Temperature increase was measured either under static conditions in the ablation area (setup 1) and at the opposite side of the mask (setup 2) or in the ablation area under dynamic conditions, rotating the whole globe to simulate a constant trephination speed with the mask positioned directly on a porcine cornea (setup 3). We used the NWL Er:YAG solid-state laser in a 1.3-mm free-running spot mode focused on the trephination margin (half of the beam on the mask and half of it on the cornea) with a pulse energy of 200 or 400 mJ and 18CrNi10 stainless steel versus three different types of ceramic masks (silicium carbide, silicium nitrite, aluminum oxide). Temperature was assessed using an infrared pyrometer with automatic data acquisition software for a personal computer. RESULTS: Overall, the temperature rise ranged between 43.6 K (metal donor mask at the trephination area with 400 mJ pulse energy) and 3.3 K (silicium carbide recipient mask at the opposite side of the mask with 200 mJ pulse energy). With all setups and both energy levels, the heating of the metal mask was significantly higher (P<0.02) than the heating of the three types of ceramic masks. The silicium carbide masks revealed the lowest temperature rise. Comparing the three setups, the temperature rise was maximal under static conditions in the ablation area and minimal at the opposite side, with the dynamic setup ranging in between. Temperature rise was significantly greater (P<0.04) in donor masks than in recipient masks for each mask material and both energy levels. CONCLUSION: The physical characteristics of silicium carbide masks seem superior to those of metal masks with regard to minimizing the thermal load of the epithelium or superficial stroma during Er:YAG laser trephination of the cornea for penetrating keratoplasty.

Animals↗

PubMed2000

Experimental evaluation of two current-generation automated microkeratomes: the Hansatome and the Supratome.

PURPOSE: To compare flap dimensions, cut quality, and blade deterioration after reuse in an experimental setting using two current-generation microkeratomes for laser-assisted in situ keratomileusis. METHODS: Two pivoting-head principle microkeratomes, the Hansatome and the Supratome, were used to perform a corneal flap in 50 freshly enucleated pig cadaver eyes, with an intended thickness of 160 microm. Provided stainless steel blades were used from one to five times. Flap diameter was measured by planimetry and thickness calculated using ultrasonic pachymetry at three different locations. Scanning electron microscopy of stromal beds and blades' cutting edges were performed to assess the cut and blade deterioration after repeated use. RESULTS: Mean flap central thickness (Hansatome/Supratome) was 151 microm (SD 18)/192 microm (SD 32). Progressive thinning/thickening of the flap was observed in the direction toward the hinge (P = .003/P = .021). Mean vertical flap diameters of 8.9 mm (SD 0.3)/8.0 mm (SD 0.4) differed significantly (P = .001). No correlation was found between thickness and diameter (r = 0.03, P = .935/r = 0.12, P = .603). At scanning electron microscopy, smooth cuts were observed with both keratomes using a new blade. Periodical chatter lines at keratectomy edge were present and were more pronounced after blade reuse. Cut quality, blade deterioration, and small tissue remnants on the blade surface were noted with repeated blade use, especially using the Supratome. CONCLUSIONS: Local flap thickness and flap diameter variations are inherent to the instrument used. Comparable cut-surface quality can be obtained with new blades. Although cut and blade deterioration appears to be minor after two reuses, the presence of tissue remnants on the blade surface still limits its reuse.

Animals↗

PubMed2000

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.

Adolescent↗

PubMed2000

[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.

Adult↗

PubMed2000

[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.

Astigmatism↗

PubMed2000

[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.

Adult↗

PubMed2000

[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.

Adolescent↗

PubMed1999

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.

Adult↗

PubMed1999

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.

Adult↗

PubMed1999

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.

Adolescent↗

PubMed1999

[Calculating the localization and dimension of the real pupil in keratoconus with ray tracing of corneal topography data].

BACKGROUND: It is crucial to center surgical procedures for optical indications on the pupil or the optical axis of the eye. In keratoconus the pupil appears to be dislocated due to optical aberrations of corneal topography. The purpose of this study was to evaluate the real pupil structure from the virtual image using exact raytracing techniques. PATIENTS AND METHODS: Eighty-eight patients with keratoconus (46 with mild and 42 with severe clinical signs) and a control group of 40 normal subjects were included in this study. Topographic height data were calculated from refraction data of a commercially available topographer (TMS-1) using a local approximation algorithm and a convex surface was modelled using a subdivision scheme. For the posterior corneal surface we postulated an aspherical surface with a central radius of curvature of 6.5 mm using Navarro's model eye. At the virtual pupil outline a bundle of parallel rays were intersected with the anterior and posterior corneal surface and refracted into the anterior chamber. The intersections of these rays with the pupil plane was defined as the real pupil outline. We assessed the amount and direction of pupil dislocation, the ratio between the virtual and real pupil size for each group and correlated these parameters with the central corneal power. RESULTS: The size of the virtual pupil exceeded the reference value of the real pupil in the normal group by 11%, in the group with mild keratoconus by 19% and in the group with severe keratoconus by 35%. The center of the virtual pupil was decentered 0.06 mm in the normal group, 0.49 in the group with mild keratoconus and 1.24 mm in the group with severe keratoconus. Whereas the direction of decentration was randomly in the normal group, we measured a preferred decentration to the inferior quadrants in mild keratoconus and a systematic decentration to the temporal inferior quadrant in severe keratoconus. Correlation of the optical dislocation did not correlate with central corneal power in any group. CONCLUSIONS: In keratoconic eyes the pupil outline is distorted and dislocated due to optical aberrations of the cornea. Exact raytracing technique allows the calculation of the real pupil outline from the virtual image and the topographic height of both corneal surfaces. Knowledge about the real pupil position may have an impact on adequate centration of keratorefractive surgery and penetrating keratoplasty.

Adult↗

PubMed1999

[Transplant endothelium and measuring corneal thickness after non-high-risk keratoplasty with briefly or long-term preserved corneal donor tissue].

PURPOSE: The corneal endothelial cell density is essential 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 after non-high-risk PK and to check for possible correlations with storage parameters of the donor corneas using two different storage methods. PATIENTS AND METHODS: Endothelial cell density (specular microscope EM 1100, TOMEY, Erlangen) and central corneal thickness (ultrasonic pachymetry SP-2000, TOMEY, Erlangen) were assessed 6 weeks, 3, 6, 9 months and one year postoperatively in 168 non-high-risk PKs. Short-term-preserved donor corneas were used in 89 patients, whereas in 79 patients organ-cultured corneas were used. The donor trephination was performed from the epithelial side using an artificial anterior chamber. The postoperative treatment with topical steroids was standardized. The mean donor post-mortem time was 9.6 +/- 8.0 hours for short-term-preserved and 17.6 +/- 10.5 hours for organ-cultured corneas (p < 0.0001). The storage time was 71 +/- 49 and 380 +/- 167 hours (p < 0.0001), respectively. RESULTS: Endothelial cell density did not differ significantly between the two storage methods (p > 0.05). At 6 weeks postoperatively, the mean endothelial cell density was 2042 +/- 675 cells/mm2 for short-term-preserved corneas and 1972 +/- 522 cells/mm2 for organ-cultured corneas (p = 0.7). Endothelial cell density did not decrease significantly (p > 0.05) within the observation period of 12 months in both groups (after 12 months: 1868 +/- 957 cells/mm2 and 1638 +/- 643 cells/mm2, respectively). The mean corneal thickness was 542 +/- 50 microns for short-term-preserved and 541 +/- 55 microns for organ-cultured corneas and remainded unchanged during the follow-up of 12 months (542 +/- 42 microns and 521 +/- 43 microns, respectively). Neither the group of short-term-preserved corneas nor organ-cultured corneas showed a significant correlation between endothelial cell density or central cornea thickness with post-mortem time or with storage time of the donor corneas at any postoperative stage (p > 0.1). CONCLUSION: During the first year after PK, only a small decrease in endothelial cell density was observed in comparison with the 6-weeks finding. The storage method does not seem to affect the short-term changes of endothelial cell density. Further long-term studies are necessary to assess the clinical relevance of these observations.

Adult↗

PubMed1999

[Keratoconus screening with wave-front parameters based on topography height data].

BACKGROUND: The image-forming properties of a keratoconus eye are degraded even in the early stage of this disease. The purpose of this study was to develop keratoconus detection scheme based on topography height data independent of the currently used system which avoids the disadvantages of detection algorithms currently used in clinical practice. PATIENTS AND METHODS: Eighty-eight patients with keratoconus (46 with mild and 42 with severe clinical signs) and a control group of 40 normal subjects were included in this study. A decomposition of corneal topography height data into orthogonal Zernike polynomials was performed using the commercially available corneal topographer TMS-1. Expansion coefficients of the different groups were compared to evaluate significant differences. Elevated terms were used to detect the disease. The statistical significance of this detection scheme was compared to those given by the keratoconus detection software of the TMS-1. From the elevated Zernike terms a neural network was constructed and optimized for dividing keratoconus patients and normal controls. RESULTS: Some low-order Zernike coefficients with a radial order n < 8 were found to be elevated in patients with keratoconus and were used to define a new detection algorithm. This index performed at least as well (sensitivity in mild/severe keratoconus 93.4%/100% with a specificity of 100%) as keratoconus detection schemes based on the Klyce-Maeda and the Rabinowitz-Klyce indices as well as the I-S value and the Surface Asymmetry Index SAI in our study population. CONCLUSIONS: Zernike decomposition of corneal topography height data allows a definition of an exact and robust algorithm for detection of keratoconus. It avoids the drawbacks of refractive power based definitions and is independent on the individual topographer design.

Adolescent↗

PubMed1999

[Topography-based calculation of keratoconus dimensions].

BACKGROUND: Keratoconus is a corneal dystrophy which usually develops in the second or third decade of life and shows various speed of progression. This disease may degrade the image-forming properties of the eye even in its early stage. The purpose of this study was to support the conventional clinical qualitative diagnostic methods of keratoconus handling with a topography-based algorithm to quantify the "ballooning" of the anterior corneal surface. PATIENTS AND METHODS: Eighty-eight patients with keratoconus (46 with mild and 42 with severe clinical signs) and a control group of 40 normal subjects were included in this study. Topographic height data were calculated from refraction data of a commercially available topographer (TMS-1) using a local approximation algorithm. A decomposition of corneal topography height data into orthogonal Zernike polynomials was performed to define a asphero-cylindrical model surface. From the difference of the raw height data and the model surface, the base, height and volume as well as the localization of the protrusion was quantified. RESULTS: The height of the corneal protrusion (23 to 71 microns), the volume of the cone (0.066 to 0.141 mm3) and the horizontal dimension (0.67 to 1.32 mm) increased highly significantly. In contrast, comparing the early to the severe stage of the disease the vertical dimension of the cone (0.64 to 0.93) changed much less. In the severe stage, the center of the protrusion was much more decentred (1.33 mm) than in the early stage (0.44) due to a shift in the inferior direction. CONCLUSIONS: The quantification of cone dimensions using corneal topography height data has the potential to assist qualitative clinical graduation in keratoconus independent of the system currently used. The knowledge about the exact amount of corneal protrusion and position of the cone may improve the assessment of the progression of the disease, thus being helpful for indication of a penetrating keratoplasty.

Adult↗