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PubMed2003

Predictive donor factors for chronic endothelial cell loss after nonmechanical penetrating keratoplasty in a regression model.

PURPOSE: To assess the diagnosis-based impact of donor parameters and trephination diameter as predictive factors on corneal endothelial cell density with an exponential regression model after nonmechanical penetrating keratoplasty (PK). METHODS: Six hundred thirty-one eyes [291 keratoconus (group I, trephination diameter 8.0 mm); 202 Fuchs' dystrophies (group II, trephination diameter 7.5 mm)-84 PK only (IIa) and 118 triple procedures (IIb); and 138 pseudophakic bullous keratopathies (group III, trephination diameter 6.5-8.0 mm)] were included in this retrospective study. The time course of the endothelial cell density (specular microscope EM 1100, Tomey, Erlangen) after PK was assessed. Endothelial cell density was analyzed in a longitudinal manner considering at least three valid postoperative cell counts (follow-up 29+/-17 months) with an exponential regression model (minimizing the residuum between observed and predicted endothelial cell count). The following potentially predictive parameters were assessed: donor age (DA), post-mortem time (PM), storage time (ST) and trephination diameter (group III). RESULTS: In the exponential regression model endothelial cell count decreased in I/II/III by 3.1+/-24.2% / 12.6+/-20.2% (IIa: 8.9+/-17.3%, IIb: 14.8+/-22.0%) / 18.7+/-27.3% annually. PM ( P=0.16 / P=0.10 / P=0.25) and DA ( P=0.20, / P=0.12 / P=0.16) did not correlate with the cell loss, but ST ( P=0.04 / P=0.04 / P=0.02) showed a mild correlation, especially in short-term-stored corneas. In group III the trephination diameter ( P=0.01) correlated inversely with the cell loss. Between short-term-preserved and organ-cultured donor corneas there was no statistically significant difference in the cell loss in any group. CONCLUSIONS: The post-mortem time and the donor age is not associated with a chronic endothelial cell loss after keratoplasty, whereas a long storage time may exaggerate the endothelial cell loss. Between short-term-preserved and organ-cultured donor corneas there was no difference in the time gradient. In bullous keratopathy patients a larger trephination size reduces the chronic endothelial cell loss.

Adolescent↗
PubMed2003

[Penetrating keratoplasty in free form using the excimer laser--first application in a patient].

BACKGROUND: Conventional mechanical trephination techniques limit penetrating keratoplasty to the use of circular transplants. Certain special indications, however, would profit from the application of non-circular transplants. We describe our first case, in which we applied a newly developed technique for congruent trephination of donor and recipient cornea in free form with the excimer laser in a patient. CASE REPORT AND METHOD: Excimer laser trephination was applied on the cornea of a 74-year old female patient who presented with a perforated peripheral corneal ulcer. The affected corneal tissue was replaced by an individually adapted transplant. Trephination was achieved by a 1.0 mm laser beam, which was guided along a predetermined pathway. RESULTS: Excimer laser trephination achieved completely congruent dimensions of donor button and recipient bed in a kidney shape. Laser trephination was carried out nearly down to Descemet's membrane. The cut in the remaining deep tissue was completed with a diamond knife. The postoperative course was uneventful. Follow-up at four months postoperatively showed a well healed clear transplant, which did not reach the optical axis of the cornea. CONCLUSIONS: This first application of the newly developed trephination technique represents a valuable addition in corneal transplant surgery in special indications. In the case demonstrated here, an eye with perforated corneal ulcer could be visually rehabilitated rapidly with only a minimal volume of transplanted tissue.

Aged↗
PubMed1984

Bone marrow biopsy technic. Artifact induced by aspiration.

Bone marrow aspiration and trephine biopsy specimens are of additive value when assessing various marrow disorders. Many physicians obtain both an aspirate and a trephine core when taking a biopsy of bone marrow, but opinions differ about which biopsy specimen should be obtained first. Some authors mention the possibility of artifactual hypocellularity and hemorrhage in the trephine biopsy specimen when trephine biopsy follows aspiration at the same site. This report describes the occurrence and significance of bone marrow aspiration artifact. The artifact usually occupies a relatively small area of the biopsy specimen and satisfactory evaluation of the marrow is still possible. However, the artifact occasionally hinders marrow evaluation, particularly when the trephine biopsy specimen is relatively short. Because the artifact is not observed in specimens obtained away from the aspiration site, it is best to perform the trephine biopsy before aspiration, or away from the aspiration site, especially when technical problems prevent obtaining a large amount of trephine material.

Biopsy, Needle↗
PubMed1994

Analysis of three methods of surgical intervention in the management of traumatic intracranial hematomas.

In the present study we discuss the methods of surgical intervention that are used in the management of traumatic intracranial hematomas in different periods after the craniocerebral trauma and the likelihood of hematoma recurrence after surgery. A total of 550 cases were retrospectively analysed. These patients were operated on employing osteoplastic trephination with a trephine Dofin, osteoclastic trephination, and osteoplastic trephination of the skull using a bone flap with 4 or 5 burr holes. The study results revealed that the greatest number of recurrences developed in the acute period of the trauma after performance of osteoclastic skull trephination. Osteoplastic trephinations using a bone flap with 4 or 5 burr holes yielded the fewest recurrences. In the periods after the fourth day of the trauma, corresponding to hematomas with subacute and chronic course, there was no statistically significant differences in the results after application of any one of the three methods of surgical interventions. A modification of the osteoplastic trephination with 4 burr holes is proposed. This method gave the best results in the operated patients in the three periods after cerebrocranial trauma.

Brain Injuries↗
PubMed1999

Management of acute complicated sinusitis: a 5-year review.

Acute sinusitis is a relatively common problem; however, sinusitis associated with a complication is less frequent. Currently there is debate as to whether acute complicated sinusitis should be managed by frontal sinus trephine and sinus washout or by immediate frontoethmoidectomy/functional endoscopic sinus surgery. To assess the effectiveness of frontal sinus trephine in the management of acute complicated frontal sinusitis, we reviewed all patients admitted to Groote Schuur Hospital with acute pansinusitis (includes frontal, maxillary, and ethmoid) from 1989 to 1993. Eighty-seven patients were admitted, of whom 43 were treated medically and 44 were treated surgically. Of the surgical patients 38 had frontal trephines and management of associated complications. Thirty (80%) of the patients who received frontal trephines recovered without further surgery, and 8 required further sinus surgery for persistent disease. Frontal trephine with management of associated complications is an acceptable management option for patients with acute complicated pansinusitis. Frontoethmoidectomy or functional endoscopic sinus surgery can be held in reserve for those patients with persistent disease that does not resolve after the initial frontal trephine.

Adolescent↗
PubMedDate not supplied

Scleral free auto-implant plug with mitomycin as limitation of trepanosclerectomy flow in glaucoma filtering surgery.

UNLABELLED: The purpose of this study is to evaluate the effect of trephination with free scleral auto-implant plug exposed to Mitomycin-C out of the eye, in surgical treatment of primary open-angle glaucoma (POAG), in comparison with efficacy of trabeculectomy with MMC (32 eyes with POAG of patients, younger than 55 years-group 1). Trephination with scleral auto-implant plug with MMC was done on 35 eyes of patients, younger than 55 years, with POAG (group 2). The postoperative follow-up was 28.52 +/- 8.78 months. SURGICAL PROCEDURE: A limbal 1.0 mm diameter trephination is made beneath the limbus-based conjunctival flap, a small iridectomy is performed. From the external layers of the trephine button one third of the corneoscleral thickness, in the form of a thin disc, is excised. The scleral disc, a free auto-implant, is dipped into liquid containing MMC with concentration 0.2 mg/ml for 5 minutes, outside the eye. Afterwards the scleral disc soaked with MMC is carefully irrigated with 150 ml of BSS and placed in the external part of the trephine fistula in primary position and stabilized with two interrupted 10-0 nylon sutures. The operation is ended as a typical trabeculectomy. The final success rate in terms of IOP (IOP < 14 mmHg) was 100%, without or with antiglaucoma medication, in both groups, but the number of postoperative complications was significantly lower in group 2. Trephination with free scleral auto-implant plug soaked with MMC may represent a viable alternative to trabeculectomy with MMC; the scleral plug may be taken out of the eye and exposed to antimetabolite outside the eye to minimize toxicity.

Antibiotics, Antineoplastic↗
PubMed1998

[Immunologic transplant reactions after non-mechanical corneal trepanation with the excimer laser].

BACKGROUND: Nonmechanical trephination has been established as the standard procedure in penetrating keratoplasty (PK) for avascular corneal diseases at our institution. The purpose of this study was to analyze the incidence and reversibility of immunologic graft reactions after nonmechanical trephination and to detect potentially causative factors. PATIENTS AND METHODS: Out of a total series of 400 nonmechanical PKs, 286 consecutive procedures with sufficient follow-up performed between 07/1989 and 09/1997 were included in the study (104 x keratoconus, 78 x Fuchs' dystrophies, 31 x bullous keratopathies, 28 x ulcers, 25 x avascular scars, 12 x stromal dystrophies, 4 x buphthalmos, 4 x others; 202 x PK only, 84 x combined procedures; 276 first PK). The age of the 138 females and 148 males at the time of surgery ranged from 16 to 89 (mean 55 +/- 19) years. The recipient and donor trephinations were performed from the epithelial side using an 193-mm excimer laser (MEL50 or MEL60, Aesculap-Meditec, 1.5 x 1.5 mm spot mode, 16-24 mJ/pulse, repetition rate 30 or 25/s; metal masks). The shape of the recipient trephination was either circular with four or eight "orientation teeth" (n = 251; 5.0-8.0 mm diameter) or elliptical (n = 35, 6.0 x 7.0 to 7.5 x 8.5 mm diameter). In 62% of procedures fresh or short-term-preserved donor tissue was used, and in 38% of procedures the donor tissue was organ-culture-preserved. RESULTS: During a mean follow-up of 22 +/- 18 months (maximum 7.7 years), 10 acute diffuse (3 irreversible; 1.0%) and 3 chronic focal endothelial graft reactions occurred (4.5%) not earlier than 4 months and not later than 35 months after PK. Elective procedures (3.5%) resulted in significantly (P = 0.01) less reactions than acute corneal ulcers (14.3%). After 1, 2 and 3 years, the cumulative reaction rates (Kaplan-Meier values) were 1.3%, 6.3% and 13.9% in elective procedures, none of which, however, occurred after 26 elliptical trephinations. With fresh or short-term-preserved donor tissue (4.2%), graft reactions did not happen more frequently but earlier (12 +/- 6 months) than with organ-culture-preserved donor tissue (2.2%, 30 +/- 6 months). In patients with keratoconus (4.9%), reactions occurred more frequently (P = 0.05, LogRank) and earlier than in patients with Fuchs' dystrophy (1.3%). CONCLUSIONS: In addition to well-established optical advantages, nonmechanical trephination seems to have no immunologic drawbacks.

Adolescent↗
PubMed2004

Manual punch versus power harvesting of osteochondral grafts.

PURPOSE: The purpose of the study was to analyze the effect on chondrocyte viability of 2 existing methods of harvesting osteochondral grafts used for articular cartilage resurfacing. TYPE OF STUDY: Acute animal experiment. METHODS: Power (P) trephine versus manual (M) punch harvesting was tested; 2.7-mm and 4.5-mm dowels were harvested from 8 femoral trochlea from 4 sheep using the Acufex MosaicPlasty system (Andover, MA). Grafts were harvested perpendicular to the articular surface to a depth of 10 mm under constant saline irrigation. Power trephine grafts (n = 46, 2.7 P; n = 45, 4.5 P) were harvested by coupling the serrated trephine to a standard orthopaedic nitrogen powered drill. Manual punch grafts (n = 41, 2.7 M; n=33, 4.5 M) were harvested by malleting the punch to the required depth, minimizing rocking, and only slightly turning the punch on removal. Five 40-microm-thick fresh cartilage sections oriented perpendicular to the articular surface were obtained from each graft and then stained with Syto 13 and ethidium bromide vital stains, and the proportion of live cells per field and physical damage were compared between groups. Masson's trichrome stain was used on paraffin-embedded histologic sections. RESULTS: Power harvesting was technically more difficult and resulted in more gross and light microscopic damage to the osteochondral grafts. Chondrocyte viability was significantly greater for manual punch versus power harvesting of both graft sizes (P <.005). Chondrocyte viability was greater for 4.5 P versus 2.7 P grafts (P <.005), but no difference was found between the 2.7 M and 4.5 M groups (P =.357). CONCLUSIONS: Chondrocyte viability is significantly greater using manual punch versus serrated power trephines when harvesting osteochondral grafts for cartilage resurfacing procedures. Power trephines should not be used for this procedure. CLINICAL RELEVANCE: This study shows that the original method (power trephine) of harvesting osteochondral grafts results in great loss of chondrocyte viability versus manual punch harvesting and should no longer be used.

Animals↗
PubMed2000

Iliac crest bone graft harvesting techniques: a comparison.

This study was undertaken to compare the morbidity of traditional iliac bone graft harvesting techniques for grafting alveolar clefts to minimally invasive techniques. Fifty-five age-matched patients, ages 6.5 to 16 years (mean, 11.2 years), 22 girls and 33 boys, were divided into three groups. The traditional bone window open harvesting technique served as the control group. Two different minimally invasive techniques, one that used a bone grinder and another that used a trephine, for bone harvesting were compared with the control. Both invasive techniques were statistically superior, p < 0.05, in terms of total time pain medication was necessary (mean of 12.0 hours for bone grinder, 17.6 hours for trephine, 26.0 hours for control), operative time for bone harvest (mean of 11 minutes for bone grinder and trephine, 20 minute for control), and mean incision length (2 cm for bone grinder and trephine, 5 cm for control). Patients exposed to the minimally invasive techniques had fewer complications, a trend toward earlier ambulation, and shorter hospital stays when compared with the bone grinder technique. The patients exposed to the bone grinder demonstrated earlier ambulation and fewer requirements for analgesia when compared with the trephine technique, although these results did not reach statistical significance. The trephine technique was useful when maxillary osteotomies were combined with alveolar bone grafting, because it provided structural bone grafts and cancellous bone. On the basis of these findings, the bone grinder is the preferred technique for harvesting alveolar bone grafts when no structural support is required. These authors no longer use the traditional bone window open harvesting technique.

Adolescent↗
PubMed2002

Percivall Pott and the miners of Cornwall.

Percivall Pott (1714-1788) was an astute and prolific mid-eighteenth century English surgeon with a strong interest in head injury. He was partial to the use of the trephine for all skull fractures and favoured early exploratory trephination when an intracranial collection could not be ruled out. If haemorrhage or abscess was beneath the dura, it was incised. Later in eighteenth century England and France, trephination fell out of favour. This was especially so in the crowded hospitals where putrid conditions were common. Surprisingly, on the remote southwestern English peninsula of Cornwall, where compound depressed skull fractures in miners were a frequent occurrence, Pott's principles prevailed unchanged. Generations of surgeons trephined early in suspected cranial fractures, without waiting for symptoms of compression or irritation. A large percentage of patients recovered. Those who died generally had diffuse injury, brain laceration, or a fractured base. The Atlantic breezes were believed beneficial to recovery. The operation of early 'preventive' trephination continued in the Cornish mining districts through the 1870s, when antiseptic methods were gradually adopted as elsewhere in England. Head injuries in miners became less common as mining reforms were introduced and head protection improved.

Coal Mining↗
PubMed1999

Stone age skull surgery in Mecklenburg-Vorpommern: a systematic study.

OBJECTIVE: Trephination of the cranial vault is the oldest known surgical procedure and has often been reported in the literature. The present study was performed to study the incidence, the techniques used, and possible indications for trephinations in the region of Mecklenburg-Vorpommern, the most northeastern German state. METHODS: One hundred thirteen of a total of 115 Neolithic (c. 2000-3500 BC) skulls and eight smaller skull fragments found in the region of Mecklenburg-Vorpommern were examined. Defects and abrasions were detected in 31 of these skulls and underwent further examination (careful microscopic and/or endoscopic examination, three-dimensional computed tomography, and x-rays). RESULTS: Six skulls showed defects resulting from trephination, mainly located along the midline or in the left parieto-occipital region. There was good osteological evidence that at least five of these operations had been survived. Two different techniques for trephination (circular cuts and scraping) had been used. CONCLUSION: From the present study, we conclude that the incidence of trephination in Neolithic skulls in our region is at least 5% and that these operations had been survived in singular cases. There is increasing evidence that these procedures were intended to be curative.

Adolescent↗
PubMed1978

[Perforating monolateral autokeratoplasty (author's transl)].

The author describes his own techniques of perforating monolateral autokeratoplasty, using two trephines of the same diameter, one of them turning with the right, the other with the left hand. To prevent loss of aqueous humor at first the one and then the other trephine is used up to half the thickness of the cornea. Then the central disc is excised, but to close the hole the trephine left in place until after the finishing of trephining the peripheral disc. The peripheral clear graft is sutured into the central hole, and the central clouded graft is sutured into the peripheral hole. The cornea is overlapped with a conjunctival flap. The diameter of the trephine may be 3 or 4 mm. In total we performed 24 perforating monolateral autokeratoplasties. In 13 the graft remained clear, in 9 they became semitransparent and in two cases they became clouded. In 20 patients the visual acuity improved, in 4 patients no change could be attained. In case of a clear healing the picture of the cornea is characteristic: in the dim center a clear disc and in the periphery - at most in the upper part - the dim graft from the leukoma.

Corneal Transplantation↗
PubMed1994

Calculation of size and location of autologous ipsilateral rotating keratoplasty.

BACKGROUND: Autologous ipsilateral rotating keratoplasty is a special form of keratoplasty in which a nonprogressive opacification of the centre of the cornea is rotated towards the limbus and the clear peripheral cornea is rotated into the optical axis of the eye. This study was performed to find an equation for calculating the best size and location of the trephine for this special kind of keratoplasty. METHODS: Geometrical calculations were used to derive the formula. RESULTS: We arrived at the following equation for the best diameter of the trephine: diameter(trephine) = 3/4 diameter(cornea)-1/2e(e = preoperative distance between corneal centre and nearest edge of opacity covering corneal centre). The postoperative diameter of the optical zone is: 2 x diameter(trephine)-diameter(cornea). A postoperative clear optical zone of half the corneal diameter is achieved if the opacity just touches but does not extend beyond the corneal centre. For a postoperative optical zone of at least 30% (40%) of the corneal diameter, the opacity is preoperatively not allowed to extend beyond the corneal centre for more than 20% (10%) of the corneal diameter. CONCLUSION: This equation can be used for calculating the optimum size and location of the trephine for autologous ipsilateral rotational keratoplasty. For that purpose it is advisable to take photographs preoperatively.

Cornea↗
PubMed1983

Influence of endothelial cell count of donor's cornea on endothelial cell loss.

In an experimental study porcine corneas were trephined using different trephining procedures. For every series of trephinations, the initial cell count of the donor cornea was found to play a role in the resulting damage induced by the cutting procedure. Pretreatment of corneas and modifications of trephining conditions did not change the negative correlations between cell count and damage due to trephining.

Animals↗
PubMed1999

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.

Adult↗
PubMed1989

Potential use of lasers for penetrating keratoplasty.

Experimental corneal trephination has been achieved with the 193 nm argon fluoride excimer and 2.9 microns hydrogen fluoride and Er:YAG laser systems. Compared with metal blades and other lasers, the 193 nm excimer laser creates the best quality corneal excision, but has a relatively slow etch rate through the stroma, and its use requires toxic gas. The mid-infrared laser systems trephine the cornea in less than 10 seconds, but cause a 10 microns to 15 microns zone of adjacent stromal damage and create wounds that are approximately 2.5 times larger than wounds made by metal scalpels. The wavelength and laser pulse duration influence the cutting characteristics of the laser. Optical delivery systems using an axicon lens, a rotating slit, and a computer controlled scanning optical system have been developed for penetrating keratoplasty. Selection of the optimal laser system for penetrating keratoplasty must await further experimental studies. Refinements of the laser cavity and delivery system are necessary before clinical studies can begin. A carefully controlled randomized clinical trial comparing laser trephination with conventional mechanical trephines will be necessary to determine the safety and efficacy of a laser trephination system.

Cornea↗
PubMed2003

[Cataract and keratoplasty--simultaneous or sequential surgery?].

BACKGROUND AND PURPOSE: Since the introduction of the triple procedure (simultaneous penetrating keratoplasty [PK], extracapsular cataract extraction [CE] and implantation of a posterior chamber intraocular lens [PCIOL]) in the mid-seventies, there is an ongoing discussion among corneal surgeons concerning the best approach for combined corneal disease and cataract. METHODS: Besides the classical triple procedure (1), two alternative microsurgical approaches are feasible: (2) CE + PCIOL prior to PK and (3) CE + PCIOL after PK. For the refractive results after TRIPLE some intraoperative details are crucial: Trephination of recipient and donor from the epithelial side without major oversize (Guided Trephine System or Nonmechanical Excimer Laser Trephination) should preserve the preoperative corneal curvature. Graft and the PCIOL placed in the bag after continuous curvilinear capsulorhexis should be centered along the optical axis. If possible, performing the capsulorhexis under controlled intraocular pressure conditions prior to trephination may help to minimise the risk of capsular ruptures. RESULTS: The major advantage of the TRIPLE is the faster visual rehabilitation and less efforts for the mostly elderly patients. However, two intraocular interventions with approach (2) and (3) bear an increased risk of infection and suprachoroidal haemorrhage. Approach (2) requires a cornea that is still transparent enough to perform cataract surgery, and the risk of intraocular pressure rise after PK seems to be increased. Approach (3) has the potential of a simultaneous reduction of astigmatism during CE (appropriate location of the incision, simultaneous refractive keratotomies or implantation of a toric PCIOL). Disadvantages may include the loss of graft endothelial cells and the theoretically increased risk of immunological allograft reactions. After TRIPLE, major deviations from target refraction have been reported. However, individual multiple regression analysis may help to minimise this problem with appropriate methods of trephination. Since suture removal after PK may result in major individual changes of the corneal curvature, IOL power calculation for approach (3) requires all sutures to be removed at the time of CE. However, even after complete suture removal the abnormal proportions between anterior and posterior curvatures and/or the irregular topographies after PK may be responsible for marked IOL power miscalculations in the individual case. CONCLUSIONS: The postulated better refractive outcome and better uncorrected visual acuity after the sequential approach is opposed by a markedly delayed visual rehabilitation. For this reason, we consider the TRIPLE procedure including CE via open sky in general anesthesia as the method of choice for combined lens and corneal opacities. Because of the often rapidly progressive nuclear cataracts after PK, we recommend the simultaneous approach in elderly patients with Fuchs' dystrophy even with incipient lens opacities.

Aged↗
PubMed2002

Superficial corneal effects of experimental nonmechanical penetrating keratoplasty using a Q-switched Er:YAG laser.

PURPOSE: To assess thermal effects of Q-switched Er:YAG laser trephination to corneal epithelium and superficial stroma using different mask types and materials for experimental penetrating keratoplasty. METHODS: Laser trephination was performed in 20 freshly-enucleated porcine eyes (repetition rate 5 Hz, pulse energy 65 mJ, spot size 0.7 mm). We used flat, open-metal and ceramic masks for donor and recipient trephination placed directly onto the corneal surface. Main outcome measures as assessed by light microscopy after PAS staining of 8-microm paraffin sections included: extension of tissue thermal damage at the cut edge in the superficial and basal epithelial layers, the basement membrane and subepithelial stroma, and depth and width of epithelial/stromal involvement in the area of the donor mask contact. RESULTS: The thermal damage in the superficial epithelium was more pronounced in donor (mean extension 61.6 +/- 15.6 microm) than in recipient (29.4 +/- 24.9 microm, p= 0.05) trephination. In donor trephination, thermal damage zone of the superficial epithelial layer was significantly smaller with ceramic than with metal masks (21.0 +/- 23.0 versus 61.6 +/- 15.6 microm, p= 0.014). In contrast, differences at basal epithelial layer (p= 0.44), basement membrane (p= 0.79), and subepithelial stroma (p= 0.2) were not statistically significant. Superficial donor involvement of the cornea adjacent to the paracentral donor mask contact zone was seen neither with ceramic nor with metal masks. CONCLUSION: Superficial corneal alterations adjacent to the mask-cornea contact zone may be minimized by using the Er:YAG laser in a Q-switched mode. Ceramic masks, in contrast to metal masks, further reduce superficial thermal alterations at the cut edge.

Animals↗