Tampa trephine penetrating keratoplasty: a tissue-tab technique for corneal transplantation. The Tampa Trephine Study Group.
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Cornea↗
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New trephine for keratoplasty (Hanna trephine).
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Corneal Transplantation↗
Some semiautomatic and automatic trephines, including an electric trephine with automatically retracting blade.
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Electricity↗
[Can the cutting performance of trephines still be improved?].
PURPOSE: Today, for the preparation of donor and recipient cornea during keratoplasty either single-use or reusable metal trephines are commonly used although excimer and femtosecond laser systems are available. Due to the surgical techniques as well as the configuration of metal trephine's cutting edge irregular corneal surfaces may be induced. These will result in a postoperative astigmatism. Contemporary manufacturing processes do allow for the production of minimal cutting edge diameters (400 nm -- 1 microm), however, this is related with a reduced mechanical stability of such delicate cutting edges. It has been observed that the cutting edge of metal blades is immediately bent with the first exposure to tissue. As a result, the cutting forces are increasing and the wound configuration is negatively effected. Due to the complex geometry of trephine cutting edges, no diamond trephines are currently available. We are investigating the cutting performance of conventional trephines that were modified using nanotechnology. METHOD: Different metal trephines were characterised using a scanning electron microscope (SEM). The diameter of the cutting edge was measured. Pig cornea were studied histologically after trepanation. Selected trephines were ion-forged in a modified PVD (physical vapour deposition) reactor using highly accelerated ions which are concentrated by magnetic fields at low temperature. The consecutive processing steps were controlled by SEM analysis of the cutting edge diameters. Randomly chosen areas of treated trephines were analysed. After processing the trephines, pig cornea were cut and analysed by histological and SEM examination. Additionally, the relevant mechanical cutting parameters of untreated as well as treated trephines were measured when penetrating into a PU (polyurethane) foil. RESULTS: Preliminary microscopic analysis already reveals differences in the quality of the cutting edges. The nanotechnological modification of the cutting edges does not result in larger diameters. Compared with the initial cutting edges, the optical analysis of the modified trephine cutting edges reveals subjectively smoother surfaces. The force measurements prove a reduction of cutting forces for the treated trephines compared to the untreated ones. The SEM analysis show for the cornea treated with the modified trephines a subjectively smoother surface. Histology reveals that the surfaces of the treated cornea do not exhibit a smooth and unidirectional structure. This divergence became larger when untreated trephines were used. The mechanical characterisation of the treated trephines resulted in harder and longer-lasting surfaces. DISCUSSION: The newly developed ion-forging of trephines in combination with nanostructured carbon coatings yield complex cutting edges of higher stability with diamond-like properties. This study shows that the performance of laser trepanation cannot be reached; however, the use of nanotechnology can further improve manual trephine techniques.
Animals↗
[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↗
[Corneal wound healing after experimental penetrating keratoplasty after excimer laser trephination in free form].
BACKGROUND: The postoperative clinical course after penetrating keratoplasty and trephination in free form using a guided excimer laser beam has been published before. Here the findings of light-microscopy comparing corneal wound healing after experimental penetrating keratoplasty after laser trephination and after conventional mechanical trephination are presented. MATERIALS AND METHODS: Homologous penetrating keratoplasty was performed on 12 NZW rabbits (6 animals with mechanical trephination, 6 animals with excimer laser trephination). The cutting edges achieved by both trephination techniques were examined by light microscopy in the remaining donor rings. During the postoperative follow-up animals were sacrificed at 3 and 6 weeks and at 3 months. Corneal specimens were retrieved and corneal healing processes were evaluated by light microscopy. RESULTS: The cutting edges of corneal excisions with the excimer laser demonstrated a high precision with only minimal collateral damage to adjacent tissue structures. At the different intervals both trephination groups demonstrated comparable stages of corneal wound healing regarding epithelial regeneration, stromal fibroblast migration with collagen synthesis and Descemet repair by endothelial synthesis of basement membrane. After 6 months corneal specimens of both groups demonstrated complete healing with nearly parallel orientation of newly synthesised collagen lamellae. Corneal thickness in the wound areas did not differ significantly from normal corneal tissue. CONCLUSIONS: Experimental follow-up studies to evaluate the feasibility of the developed technology of laser trephination in the living eye have shown no differences between conventional mechanical and excimer laser trephination with a guided beam. The present histology study also does not demonstrate any significant differences in corneal wound healing between the two trephination groups. Although excimer laser trephination along metal masks has now been established for several years, the here presented technique for trephination with individualised transplant geometries appears to be a valuable addition to the surgical repertoire in the presence of selected corneal pathologies.
Animals↗
The Tampa Trephine technique with cat corneal endothelium.
The Tampa Trephine (Martin Marietta Speciality Components, Largo, FL, U.S.A.) penetrating keratoplasty technique uses a 7.0-mm corneal donor button with six rectangular 1 x 2-mm tabs of Bowman's layer, 75 microns in thickness, which are inserted into the recipient stroma beneath Bowman's layer. We evaluated the safety of the Tampa Trephine tissue-trephination method on the cat corneal endothelium combining vital staining and scanning electron microscopy, comparing it with the standard Weck trephination technique. The Tampa Trephine tissue trephination produces a donor button with a 6.7-mm diameter central area of normal endothelium. Localized peripheral areas of cellular loss, endothelial and Descemet's tears, endothelial detachment, and folding along the border of the trephination were observed with the Tampa Trephine method, all located in an area of < or = 150 microns, adjacent to the edge of the button. Standard trephination induced a localized peripheral area of endothelial damage < 50 microns in extension from the donor edge. A theoretic maximal 8.4% peripheral endothelial cell loss is induced with the Tampa Trephine trephination method, compared with a 2.8% loss with the standard procedure. The peripheral location of the alterations after the Tampa Trephine does not hinder the viability of the corneal endothelium, as it has been clinically observed.
Animals↗
Excimer laser "corneal shaping": a new technique for customized trephination in penetrating keratoplasty. First experimental results in rabbits.
PURPOSE: The aim of the presented experimental work was to develop a technique for congruent trephination of donor and recipient corneas in free form using a 193-nm excimer laser and to study the clinical follow-up after the application of the technique in a rabbit model. METHODS: In 12 New Zealand White rabbits homologous penetrating keratoplasty was performed. Trephination of donor buttons and recipient beds was achieved in six animals by conventional mechanical trephination and in six by excimer laser trephination with a guided laser beam in a non-circular geometry. The surgical procedure and its applicability to human subjects were evaluated and the postoperative clinical course was followed for 6 months. RESULTS: The surgical procedure of full-thickness excimer laser trephination could be performed reproducibly in the animal model both for dissection of the donor buttons and for preparation of the recipient beds. Keratoplasty was performed with kidney-shaped transplants after trephination in free form with the guided laser beam. Postoperative clinical follow-up did not show any differences between the two trephination groups that could be related to the applied trephination technique. After 6 months we observed well-adapted and clear corneal grafts, kidney-shaped in the excimer trephination group and circular in the mechanical trephination group. No side effects on the crystalline lens and the central retina could be clinically observed following excimer laser trephination. CONCLUSION: We present the first experimental study of keratoplasty with freely selected transplant geometry and perfect congruence of donor button and recipient bed. The application of this technique in certain corneal disorders in humans will offer improved treatment options in the future.
Animals↗
Audit of bone marrow trephines.
AIMS: To establish criteria of adequacy for bone marrow trephine biopsy specimens and to audit the quality of trephines performed at the Christie Hospital, Manchester. METHODS: Trephines (n = 767) performed over 12 months were reviewed. Their lengths, and the lengths of their constituent parts (soft tissue, cortex, crushed marrow and interpretable marrow) were measured. The mean performance of each operator was calculated. Criteria of adequacy were established by a review of the published findings and an analysis of the relation between trephine length and the rate of infiltration by tumour. RESULTS: Before processing, the average trephine was 1.59 cm long. Trephines shrunk by 25% during processing. In histological sections the average length was 1.15 cm, consisting of 0.09 cm of soft tissue, 0.04 cm of cortex, 0.26 cm of disrupted marrow and 0.74 cm of interpretable marrow. A large number of operators were taking trephine biopsy specimens and their performance varied considerably. Review of the published findings suggested that the minimum adequate length is in the range 1.5 cm to 2.0 cm. The analysis of the relation between length of trephine and the rate of positivity for neoplasia yielded a minimum adequate length of 1.2 cm in section (1.6 cm before processing). Fifty eight per cent of the trephines were inadequate by this criterion. There was a tendency for the Jamshidi needle to produce a longer trephine than the Islam needle. CONCLUSION: According to objective criteria, at the Christie Hospital, many operators are producing a high proportion of inadequate bone marrow trephines.
Biopsy, Needle↗
Astigmatism after penetrating keratoplasty using the Krumeich guided trephine system.
BACKGROUND: The use of a suction trephine during penetrating keratoplasty has the potential to reduce trephination errors and astigmatism after suture removal. METHODS: In this study, we evaluated refractive astigmatism after suture removal in 26 eyes that had penetrating keratoplasty for keratoconus using refraction, keratometry, and videokeratography. Group I (11 eyes) had manual trephination with an open disposable blade of both the donor (8.2 mm) and the recipient (8.0 mm). Group II (10 eyes) had manual trephination with an open disposable blade of the donor (8.2 mm) and Krumeich guided trephine system trephination of the recipient (8.0 mm). Group III (5 eyes) had guided trephination of both the donor (8.0 mm) and the recipient (8.0 mm). RESULTS: The guided trephine groups II and III demonstrated statistically significant less refractive cylinder when compared to manual trephination group I (p < .01). The mean keratometric cylinder for group I was 6.50 diopters (D) (range, 1.50 to 9.00 D), for group II was 3.00 D (range, 0.50 to 7.00 D), and for group III was 2.55 D (range, 0 to 4.00 D). CONCLUSION: The Krumeich guided trephine system produced less keratometric astigmatism than manual trephination after penetrating keratoplasty for keratoconus.
Astigmatism↗
The regularity of laser keratectomy depth in nonmechanical trephination for penetrating keratoplasty.
BACKGROUND AND OBJECTIVES: To study the regularity of laser keratectomy depth in nonmechanical trephination for penetrating keratoplasty (PK) and to assess its implications on astigmatism and visual acuity (VA). PATIENTS AND METHODS: In this retrospective clinicopathologic study, the authors enrolled 26 women and 32 men (mean age 54 +/- 20 years) with either keratoconus (n = 27) or Fuchs' dystrophy (n = 31), who underwent excimer laser (193 nm) trephination using a manually guided beam. Donor cornea trephination was performed using an artificial anterior chamber and either an automated rotation device (n = 27) or a manually guided beam (n = 31). The minimum residual corneal thickness (MRCT) and the random residual corneal thickness (RRCT), requiring division with scissors in excised patient buttons or corneoscleral donor rims, were assessed in a masked fashion using histologic sections. The postkeratoplasty keratometric net astigmatism, the subjective cylinder, and the VA were evaluated before and after suture removal. RESULTS: In patients with keratoconus, the mean MRCT (13% +/- 14%) and RRCT (38% +/- 20%) were significantly higher than in the patients with Fuchs' dystrophy (7% +/- 11% and 26% +/- 15%, respectively) (P < .01). When an automated rotation device for trephination of the donor cornea was used, the mean MRCT (2% +/- 4%) and RRCT (14% +/- 11%) were significantly smaller than when a manually guided laser beam was employed (15% +/- 12% and 38% +/- 15%, respectively) (P < .001). After suture removal, the VA increased significantly with automated trephination (P = .04), but not with manually guided trephination of the donor cornea (P = .24). However, after a mean follow-up of 30 +/- 8 months, the differences in the mean keratometric astigmatism, refractive cylinder, and VA after automated trephination (3.0 D, 2.6 D, 20/29, respectively) compared with those after manually guided trephination of the donor cornea (4.3 D, 3.9 D, 20/33, respectively) did not reach statistical significance. CONCLUSIONS: The regularity of donor trephination depth can be significantly improved by using an automated rotation device instead of a manually guided beam. Although residual postkeratoplasty astigmatism was not directly related to trephination depth, the improvement of the functional results after suture removal seems to be promoted by automated trephination.
Astigmatism↗
Comparison of relative value of bone marrow aspirates and bone marrow trephine biopsies in the diagnosis of solid tumor metastasis and Hodgkin lymphoma: institutional experience and literature review.
CONTEXT: Bone marrow aspirates as well as bone marrow trephine biopsies are frequently performed to assess whether there is marrow involvement by a malignancy. Numerous reports differ in the relative value of these 2 procedures and fail to provide concise guidelines that can help choose the appropriate technique in this clinical situation. OBJECTIVE: To compare the relative value of aspirates and trephine biopsies in the diagnosis of solid tumor metastasis and Hodgkin lymphoma. In addition, we correlate our findings with those of the literature to provide a concise practice guideline. DESIGN: Sixty-six cases showing bone marrow involvement by solid tumor and Hodgkin lymphoma in bone marrow aspirates, bone marrow trephine biopsies, or both were included in the study. The diagnosis and findings made on aspirates were compared with those made on trephine biopsies in each case. RESULTS: In those cases where both aspirate and trephine biopsy were available for evaluation, there was a 22% positive correlation in the findings on aspirates and trephine biopsies. The correlation between aspirates and trephine biopsies was highest in cases of small cell carcinoma of the lung (3/11, or 36.3%) followed by breast carcinoma (7/20, or 35%), prostate carcinoma (1/9, or 11.1%), and Hodgkin lymphoma (1/20, or 5%). Two of 5 cases from the miscellaneous category demonstrated simultaneous involvement of aspirate and trephine biopsy by a gastric carcinoma as well as an adrenal gland carcinoma. CONCLUSIONS: Bone marrow aspirate and bone marrow trephine biopsy should both be performed in patients with proven or suspected malignancies where staging may affect management. However, bone marrow aspirate has only a minimal role, if any, in detecting bone marrow involvement by Hodgkin lymphoma. In cases of breast carcinoma, small cell carcinoma of lung, and prostate carcinoma, aspirate evaluation may confirm trephine biopsy results or, more rarely, provide the sole confirmation of the malignancy.
Biopsy↗
Behavioral and neurochemical asymmetries following unilateral trephination of the rat skull: is this control operation always appropriate?
The present results are from rats that were intended as sham-operated controls in a study of unilateral lesion of the cortical barrel fields. These animals received a trephine hole through the skull, centered over the barrel fields of one hemisphere. Unexpectedly, they showed time-dependent behavioral and neurochemical asymmetries: 1 + 4 days after unilateral skull trephination they scanned an open field mainly with the contralateral vibrissae. Thereafter (days 7 + 14), scanning recovered to symmetry; however, an ipsilateral asymmetry was induced now by challenge with the dopamine receptor agonist apomorphine. At the same time period after skull trephination, an asymmetry of thigmotactic swimming had developed, with more thigmotactic swimming ipsilateral to the side of skull trephination. Neurochemically, there were indications for changes in neostriatal dopamine metabolism because the tissue levels of dopamine and dihydroxyphenylacetic acid were lower on the ipsilateral side in animals killed 6-16 days after trephination. The time courses of behavioral and neurochemical asymmetries after unilateral skull trephination paralleled those seen following unilateral barrel cortex lesion or unilateral removal of the corresponding contralateral vibrissae; however, without exception, the asymmetries after trephination were in the opposite direction than after cortex lesion or vibrissae removal. The possible mechanisms by which skull trephination might have affected behavior and neurochemistry are discussed, especially with respect to the vibrissae-barrel cortex system and the basal ganglia. Because trephination of the skull is routinely employed, both as a control procedure and for CNS manipulation, these results may have important implications for the design of future experiments.
3,4-Dihydroxyphenylacetic Acid↗
[Immunological graft reactions after penetrating keratoplasty - A prospective randomized trial comparing corneal excimer laser and motor trephination].
BACKGROUND AND PURPOSE: Nonmechanical trephination has been established as an advantageous procedure in penetrating keratoplasty (PK) for avascular corneal diseases and has been performed successfully in more than 1000 eyes at our institution. The purpose of this study was to compare incidence, type and reversibility of immunological graft reactions after mechanical and nonmechanical trephination for PK. PATIENTS AND METHODS: As part of a prospective randomized clinical trial 179 eyes of 76 females and 103 males were included, that had primary central PK without previous intraocular surgery between 10/1992 and 12/1997 for Fuchs' dystrophy (diameter 7.5 mm, n=73) or keratoconus (8.0 mm, n=106). The recipient and donor trephinations were performed from the epithelial side using either a motor trephine (Microkeratron, Geuder, n=91) or an 193-nm excimer laser (MEL60, Aesculap-Meditec, 1.5 x 1.5 mm spot mode, 16 - 24 mJ/pulse, repetition rate 25/s) along round metal masks with 8 "orientation teeth/notches" (n=88). As a routine, donor oversize was 0.1 mm. 128 patients (72 %) had PK only, 51 patients had simultaneous cataract extraction and PC-IOL implantation (triple procedure). Wound closure was achieved using a 16-bite double running diagonal suture by one surgeon (G.O.H.N.). In 53 % of procedures short-term-preserved donor tissue, in 47 % organ-cultured tissue was used. The mean patient/donor age was 51 +/- 17/57 +/- 19 years with nonmechanical trephination and 50 +/- 19/58 +/- 20 years with mechanical trephination. Incidence, type and reversibility of endothelial immunologic graft reactions were recorded continuously by clinical follow-up in an outpatient service with cornea specialization (after 6 weeks, then every 3 months until after suture removal, then every half year). RESULTS: During a mean follow-up of 40 +/- 15 months, 7.3 % of eyes developed an immunological endothelial graft reaction. Acute diffuse (5.6 %) were more frequent than chronic focal reactions (1.7 %). Only 1.7 % of grafts became irreversibly cloudy. More than 80 % of all graft reactions occurred later than one year (on average 23 +/- 13 months) after PK. Neither incidence (p=0.82, Chi square test) nor cumulative 3-year-rate of immunological graft reactions (p=0.91, LogRank test) differed significantly comparing nonmechanical (6.8 % or 7.3 %) and mechanical (7.7 % or 5.6 %) trephination. In eyes with keratoconus (6.6 %, 16 +/- 8 months) graft reactions did not occur more frequently (p=0.68) but earlier (p=0.02) than in eyes with Fuchs' dystrophy (8.2 %, 31 +/- 11 months). Donor age, post-mortem-time and preservation period did not significantly affect the rate of graft reactions in our study setting. CONCLUSIONS: Besides well-established optical advantages, nonmechanical trephination using the excimer laser seems to have no immunologic drawbacks in contrast to conventional mechanical trephination. Donor parameters appear to have no major impact on the incidence of graft reactions after non-high-risk PK. Rather, an adequate postoperative therapy with topical steroids, an informed patients' compliance, a consequent long-term follow-up in a clinical out-patient service with corneal specialization and a good education of and cooperation with the referring ophthalmologists are of utmost importance for the clear corneal graft in the long run.
Adolescent↗
Audit of bone marrow aspirates and trephine biopsies in multiple myeloma--a single centre study.
We compared 79 simultaneous marrow aspirates and trephine biopsies from multiple myeloma patients for sensitivity, concordance, quality and clinical relevance. A total of 60 examinations had been performed for initial diagnosis, i.e. in cases of suspected myeloma and 19 at follow-up. Of which, 45 (57%) of trephine biopsies were less than 1.6 cm before processing and 33 (42%) were crushed and/or fragmented. Overall, only 19/79 (24%) of trephine biopsy specimens were of at least 1.6 cm length prior to processing and not disrupted. On the other hand, 75% of aspirates were particulate and satisfactory. Mean time between receipt of a trephine biopsy specimen and issuance of a histopathological report was 9 days. Although 40% of trephine biopsies yielded information that could not be reliably obtained from a bone marrow aspirate such information was in all cases clinically irrelevant or obtainable by non-invasive means. In all cases where myeloma was detected in a trephine biopsy it was also detected in a simultaneous bone marrow aspirate, if particulate. However, there were four (5%) cases in which myeloma was detected in such aspirates but not in simultaneously taken trephine biopsies. In cases (n=19) where repeat aspirates/trephine biopsies were taken for surveillance, concordance was found between reported changes in plasma cell ratio. Our data failed to demonstrate any added benefit from routinely performing trephine biopsies after a particulate specimen had been aspirated for the diagnosis or surveillance of myeloma. Furthermore, they suggest that particulate aspirates may be at least as sensitive as trephine biopsies for detecting myeloma.
Adult↗
Thermal effects in excimer laser trephination of the cornea.
BACKGROUND: Excimer laser trephination, as an alternative to mechanical trephination of the cornea in penetrating keratoplasty, is expected to reduce long-term postkeratoplasty astigmatism. Trephination with high energy densities may induce thermal epithelial alterations when metal aperture masks are used. METHODS: Ninety porcine eyes fixed in an artificial anterior chamber (20 mmHg) were trephined with a 193-nm excimer laser in order to study the effect of the temperature on the cornea and the aperture mask during and after termination of the laser exposure. Energy levels tested were in the range used in patients. A pyroelectric infrared sensor connected to a PC via an analog-digital converter was used. With a high-speed sampling routine written in C+2 it was possible to monitor on line the temperature in a focus 0.8 mm in diameter. RESULTS: In donor trephination the maximum temperature increase of the metal mask was 11 K (donor tissue 6.1 K, repetition rate 30/s). During recipient trephination the maximum temperature increase of the mask was 9.4 K (7.5 K on the cornea). An increase in the repetition rate and a decrease in the rotation speed resulted in greater temperature increase of the exposed cornea or metal mask. CONCLUSIONS: Online monitoring of cornea and mask surface temperatures during excimer laser trephination is possible using high-speed sampling equipment. Appropriate adjustment of repetition rate and rotation speed may reduce thermal effects, especially in donor trephination.
Animals↗
Penetrating keratoplasty for keratoconus: role of videokeratoscopy and trephine sizing.
PURPOSE: To evaluate whether determining graft-host trephine disparity on the basis of videokeratoscopic data of keratoconus patients having penetrating keratoplasty (PKP) reduces ametropia and to correlate preoperative videokeratoscopic values, posterior axial length (PAL), and trephine disparity with postoperative refractive outcomes. SETTING: Hôtel-Dieu, University of Paris, France. METHODS: This randomized clinical trial comprised 18 keratoconus patients who had PKP. After computerized videokeratoscopic analysis, patients were randomly assigned to a test or control group with matching for midperipheral corneal keratoscopic criteria. One surgeon performed all grafts using the same technique (except for donor button punching with an 8.00 or 8.25 mm blade, depending on preoperative keratoscopy) with suction trephination (8.00) and a running 10-0 nylon suture. The PAL (total axial length minus the distance from the anterior corneal surface to the anterior lens surface) was measured by applanation ultrasonography. Refraction and videokeratoscopic analysis were done 18 months postoperatively (6 months after suture removal). RESULTS: The mean deviation from emmetropia corrected for PAL in test group patients who had trephine sizing based on the hypothesis that preoperative videokeratoscopy is a useful determining factor was 1.12 diopters (D) +/- 0.74 (SD), which was significantly smaller (P = .005) than that in the control group (2.19 +/- 0.85 D). The test group had uncorrected visual acuities of 20/50 or better. Postoperative spherical equivalent was affected by PAL (P = .0001), preoperative keratoscopy (P = .0001), and trephine disparity (P = .01). Central corneal power after grafting was influenced by keratoscopy (P = .0001) and trephine disparity (P = .002). Uncorrected visual acuity was affected by PAL (P = .001) and keratoscopic data (P = .01). CONCLUSIONS: Parameters for reducing ametropia after grafting of keratoconus patients can be developed for each surgeon based on trephine disparity dependent on preoperative keratoscopic values of the recipient midperipheral cornea and PAL. If the PAL is between 19.0 and 21.0 mm, preoperative midperipheral corneal videokeratoscopy to choose same-size or 0.25 mm different donor and recipient trephine blades is useful to achieve refractive results approximating emmetropia with the described technique.
Adolescent↗
[Impact of intracameral pressure on donor cut angles in nonmechanical Er:YAG laser trephination for penetrating keratoplasty].
BACKGROUND AND PURPOSE: Congruent cut surfaces are a predisposition for good apposition of donor and recipient during penetrating keratoplasty (PK). The purpose of this study was to assess the impact of the intracameral pressure during nonmechanical donor trephination from the epithelial side on the cut angles for experimental human PK. METHODS: With a Q-switched 2.94 micro m Er : YAG laser a 6 mm sized corneal donor trephination was performed subtotally in 30 human corneas using an artificial anterior chamber device allowing different intracameral pressures (10, 20, and 40 mm Hg). The cut angles were measured immediately after the trephination by ultrasound biomicroscopy (UBM) at four quadrants: between trephination cut and corneal epithelium (angle 1 = A1-UBM) and between trephination cut and horizontal plane (angle 2 = A2-UBM). The positions of the measures were marked, the corneas were fixed in a buffered 10 % paraformaldehyde solution, and the same positions were analyzed by histology. The histological cuts were digitized, the images printed, and the cut angles measured in paper (A1-histology). RESULTS: Mean angles were 111.6 degrees /113.5 degrees /126.6 degrees (A1-UBM), 88.4 degrees /93.5 degrees /101.8 degrees (A2-UBM) and 120.4 degrees /125.1 degrees /119.3 degrees (A1-histology) with 10/20/40 mm Hg, respectively. The A2-UBM showed a significant increase of divergence with increasing intracameral pressure (p < 0.03). For A1-UBM cut angles with 10 and 20 mm Hg were significantly smaller compared to those with 40 mm Hg (p < 0.002), but there was no difference of divergence between 10 and 20 mm Hg. The A1-histology cut angle showed no correlation with intracameral pressure (p > 0.09). CONCLUSIONS: Increasing intracameral pressure using an artificial anterior chamber during donor trephination from the epithelial side for nonmechanical PK using Er : YAG laser results in increasing divergence of cut angles. This may disturb the congruence of the cut angles in donor-recipient apposition. To achieve standardised cut angles for a good donor recipient apposition, similar normotonic intracameral pressures for donor and recipient trephination should be attempted. The UBM has the potential to analyse the cut angle immediately after subtotal trephination preserving the attempted intracameral pressure in the artificial anterior chamber. Histological analysis of the cut angles seems to lack methodological validity.
Anterior Chamber↗