The influence of corneal stromal matrix proteins on the migration of human corneal fibroblasts

Motivated by the alterations seen in the corneal matrix composition after photorefractive keratectomy and the migration of corneal keratocytes seen following this procedure, the locomotor response of corneal stromal fibroblasts to various extracellular matrix proteins was determined. In addition, the involvement of integrin mediated attachment to the matrix proteins was investigated. Quantitative invasion assays were performed using collagen gels, supplemented with either fibronectin, tenascin, collagen type V, collagen type VI, chondroitin sulfate or keratan sulfate. The ultrastructure of the gels was visualized by scanning electron microscopy and related to the migration results. The extent of alpha(1)beta(1), alpha(2)beta(1), alpha(3)beta(1)and alpha(5)beta(1)integrin mediated attachment to the matrix proteins was evaluated using blocking antibodies. Fibronectin increased corneal fibroblast migration significantly, and served as an excellent substrate for cellular attachment, mediated by the alpha(5)beta(1)integrin. Addition of tenascin to the fibronectin-containing gels disrupted these effects, while attachment to this matrix also involved the integrins alpha(2)beta(1)and alpha(3)beta(1). Chondroitin sulfate and collagen types V and VI primarily altered the structure of the collagen matrix, resulting in an inhibition of migration by the collagens and an increase by chondroitin sulfate. They all served as poor substrates for attachment. Thus, the migratory activity of corneal fibroblasts in vitro is influenced by the composition of the surrounding extracellular matrix, either by integrin mediated cell-matrix interactions or through matrix-matrix interactions. This study provides evidence that the provisional matrix deposited in a corneal stromal wound may facilitate the entry of migrating corneal fibroblasts.

A clinical comparison of the Xpert non-contact tonometer with the Goldmann applanation tonometer after penetrating keratoplasty

PURPOSE

To assess the agreement between the Xpert non-contact tonometer (NCT) and the Goldmann applanation tonometer in patients who have undergone penetrating keratoplasty.

METHODS

The study material consisted of 42 consecutive patients (43 eyes) who had undergone penetrating keratoplasty within the previous 13 months.

RESULTS

The slope of the linear relationship between the two measurement methods did not differ significantly from 1.0. The mean difference between the methods of 0.96 mmHg was not statistically significant. The range of intraindividual differences between the methods was from -9.8 to 22.8 mmHg. The standard deviation of differences was 6.62 mmHg. The 95% limits of agreement were -12.00 to 13.94 mmHg. There was no significant correlation between the central corneal thickness, astigmatism or transplant size and the difference between the methods

CONCLUSION

The Xpert NCT shows considerable variation from the Goldmann values The degree of agreement with the true IOP value remains to be shown.

Prolonged persistence on the ocular surface of fortified gentamicin ointment as compared to fortified gentamicin eye drops

PURPOSE

A comparative study on the elimination of gentamicin from the ocular surface and the concentration of gentamicin in the anterior chamber following application of either an ointment or eye drops containing equal concentrations (1.5%) of gentamicin.

METHODS

A disc-diffusion test was used to determine the concentration of gentamicin in fornix inferior of 10 persons. The anterior chamber concentration of gentamicin was determined in 5 cataract patients by the TDX analyzer, Abbot Laboratories, II., USA.

RESULTS

Ten minutes following application, the concentration of gentamicin was significantly higher in the eyes receiving ointment (310.6 mg/L) compared to drops (45 mg/L) (p<0.01). Furthermore, gentamicin could be detected 40 minutes after application in the eyes receiving ointment compared to 10 minutes in the eyes receiving drops. The anterior chamber concentration of gentamicin after application of either drops or ointment was lower than 0.6 mg/L and thus below detection limit.

CONCLUSIONS

The persistence of gentamicin ointment was significantly longer on the ocular surface as compared to gentamicin eye drops. Gentamycin ointment may thus provide a means to reduce the high application frequency presently in use with eye drops to treat bacterial keratitis and thereby reduce patient inconvenience, especially during nighttime.

Comparison of endothelial cell density estimated by contact and non-contact specular microscopy

PURPOSE

To compare a contact and a non-contact specular microscope in the determination of endothelial cell density.

SUBJECTS AND METHODS

One hundred and twenty-one eyes from 70 patients who had undergone various degrees of photorefractive keratectomy for myopia were included. The endothelium was imaged by contact (Konan Clinical Specular Microscope) and non-contact (Topcon SP-1000) specular microscopy and the endothelial cell density estimated.

RESULTS

The average endothelial cell density achieved by the contact specular microscope was 3011+/-298 cells/mm2 (mean+/-SD, n=121) and by the non-contact specular microscope 3015+/-265 cells/mm2 (n= 121). The difference in endothelial cell density between the contact and the non-contact specular microscope (contact minus non-contact) was -4+/-175 cells/mm2 (t=0.26, 2p>0.05 in a paired t-test). The sampling error on the estimated endothelial cell density was 76 cells/mm2 for the contact specular microscope and 74 cells/mm2 for the non-contact specular microscope.

CONCLUSION

The average endothelial cell density and the precision of the measuring technique were similar for the contact and the non-contact specular microscope. Furthermore, the endothelial cell densities estimated by the two instruments at various values of anterior central corneal refractive power and central corneal thickness were similar. The two instruments can be used interchangeably.

Magnification changes in specular microscopy after corneal refractive surgery

PURPOSE

To describe the effect of corneal refractive surgery on the magnification of a contact and a non-contact specular microscope.

METHOD

The magnification of a contact specular microscope (Konan Clinical Specular Microscope) and a non-contact specular microscope (Topcon SP-1000) was experimentally and theoretically studied as a function of anterior corneal refractive power and central corneal thickness.

RESULTS

The magnification of the contact and non-contact specular microscope was found to decrease slightly with decreasing central corneal thickness. In addition, the magnification of the non-contact specular microscope decreased slightly with decreasing anterior corneal refractive power.

CONCLUSION

As the preoperative and postoperative measuring conditions are different in patients undergoing corneal refractive surgery a correction for magnification changes is necessary when small changes in endothelial cell density are looked for.

Corneal transplantation with donor tissue kept in organ culture for 7 weeks

PURPOSE

To study the fate of corneal grafts after extended organ culture (7 weeks).

METHODS

Six patients with symmetrical eye diseases were grafted bilaterally, in one eye with a cornea prepared by routine organ culture (mean 16 days), in the other eye with a donor cornea kept for 7 weeks (mean 49 days) in organ culture. The outcome was evaluated by biomicroscopy, graft thickness, endothelial cell density and visual performance after an observation time of at least 1 year.

RESULTS

Penetrating 7-8 mm grafting was uncomplicated in all cases. The endothelial densities were in both groups in the range 1000-2000 cells/mm2, and visual acuity 0.2-0.9 in cases with no other ocular pathology. Postoperative graft thickness and deswelling did not differ between 2- and 7-week cultured corneas. At final examination the thicknesses were 0.50 mm and 0.49 mm for 2- and 7-weeks cultured corneas.

CONCLUSION

Seven-week cultured corneas give clinical results comparable to those obtained using shorter culture periods. An extended culture period may be used to improve other qualities of the graft (compatibility, cell number, cell metabolism) and microbiological control.

A morphological and functional study of Congenital Hereditary Endothelial Dystrophy

PURPOSE

To contribute to the basic understanding of Congenital Hereditary Endothelial Dystrophy (CHED) by clinical, functional, and histopathological examinations of three cases.

METHODS

Prior to grafting, corneas were evaluated by slit lamp examination and by assessment of endothelial permeability to fluorescein. Following penetrating keratoplasty, corneal buttons were evaluated by light- and electron microscopy and by assessment of stromal swelling pressure.

RESULTS

Patients with CHED had a markedly increased corneal thickness (0.93-0.98 mm) with epithelial oedema and a stromal swelling pressure close to zero; suggesting that the stroma was maximally swollen in vivo. Corneal endothelium showed an increased permeability to fluorescein; suggesting a functional barrier defect. Histopathological evaluation revealed: 1) a normal endothelial cell density; 2) an abnormal endothelial morphology with irregular and multi-nucleated cells containing abnormal cell organelles; and 3) a profound thickening of Descemet's membrane, 16-18 microm, with multiple focal areas of abnormal fibrillar deposits in the posterior half.

CONCLUSIONS

This study suggests that the primary defect in patients with CHED is a degenerated and dysfunctional corneal endothelium, characterized by an increased permeability and an abnormal and accelerated Descemet's membrane secretion. The underlying pathophysiological mechanism(s) may be related to an abnormal endothelial barrier function, leading to secondary swelling of the stroma and epithelium. Further studies are needed to identify the specific functional defect(s) and the embryological origin of the abnormal corneal endothelium in CHED.

Endothelial cell loss after photorefractive keratectomy for myopia

PURPOSE

To study the long-term effect of 193 nm excimer laser photorefractive keratectomy (PRK) on the human corneal endothelial cell density.

SUBJECTS AND METHODS

One hundred and twenty-four eyes from 71 patients underwent photorefractive keratectomy for myopia or myopic-astigmatism. Endothelial cell density was examined a short time before the operation and on an average of 50 months after the operation using a contact specular microscope. A subgroup of 32 eyes from 20 patients treated only once was examined preoperatively and 7 and 52 months postoperatively. The endothelial cell densities were corrected for the changing magnification of the contact specular microscope with changing central corneal thickness and for the expected physiological cell loss with time.

RESULTS

The average endothelial cell density was preoperatively 3098+/-283 cells/mm2 (mean+/-SD) and postoperatively 3048+/-294 cells/mm2 corresponding to a change of -50+/-157 cells/mm2. This was statistically significantly different from zero in a paired t-test (n=124, t=3.58, 2p<0.001). The average changes in endothelial cell density for the subgroup were -34+/-159 cells/mm2 for the postoperative time interval 0-7 months and -20+/-188 cells/mm2 for the postoperative time interval 7-52 months. These results were not statistically significantly different from zero in a paired t-test (n=32, t=1.21 and t=0.60, 2p>0.05). A statistically significant negative correlation between preoperative cell density and the change in cell density was found (n=124, r=-0.21, 2p<0.05).

CONCLUSION

This study suggests a potentially harmful effect of PRK on the human corneal endothelium. It appears that most cells are lost during ablation or within the first period of time after PRK.

Paired arcuate keratotomy for congenital and post-keratoplasty astigmatism

PURPOSE

To study the effect of arcuate keratotomy on corneal astigmatism in previously grafted eyes compared to eyes with naturally occurring astigmatism.

SUBJECTS AND METHODS

Twenty-three eyes with naturally occurring astigmatism and 21 eyes with post-keratoplasty astigmatism were treated by arcuate keratotomies in the steepest corneal meridian. Visual acuity, spherically equivalent refraction, and refractive cylinder were measured before surgery and 1 to 10 years after the operation.

RESULTS

The preoperative refractive cylinder was reduced from 5.0 dioptres (median) to 1.25 dioptres in eyes with natural astigmatism and from 7.0 dioptres to 3.25 dioptres in post-keratoplasty eyes. Spherical equivalent refraction changed from -0.6 dioptres to -1.5 dioptres in eyes with natural astigmatism and from -3.5 dioptres to -4.5 dioptres in previously grafted eyes. The induced change in astigmatism, as calculated by Fourier analysis, correlated strongly with the existing preoperative astigmatism. The effect of the procedure did not correlate with the type of astigmatism (congenital vs. post-keratoplasty), time after surgery, or with patient age or sex.

CONCLUSION

Arcuate keratotomy is a simple procedure to reduce naturally occurring astigmatism as well as induced astigmatism after keratoplasty. Parallel to the astigmatic change, negligible changes in the spherical equivalent are induced.

Chemotaxis of human keratocytes is increased by platelet-derived growth factor-BB, epidermal growth factor, transforming growth factor-alpha, acidic fibroblast growth factor, insulin-like growth factor-I, and transforming growth factor-beta

PURPOSE

Following corneal wounding, early migration of keratocytes into the wound area is of pivotal importance in the healing process, but the nature of this migration is not well understood. The influence of peptide growth factors on the chemotactic and chemokinetic migration of human corneal keratocytes was investigated, using the following growth factors: platelet derived growth factor-BB (PDGF-BB), epidermal growth factor (EGF), transforming growth factor-alpha (TGF-alpha), acidic fibroblast growth factor (aFGF), basic fibroblast growth factor (bFGF), insulin-like growth factor-I (IGF-I), and transforming growth factor-beta-1 (TGF-beta 1).

METHODS

The chemotactic stimulation was investigated in the Boyden blind-well chemotaxis chamber, and the chemokinetic effect of the growth factors determined by a modified checker-board analysis.

RESULTS

PDGF-BB, EGF and TGF-beta 1 stimulated chemotaxis towards a peak value, with a subsequent decline at higher concentrations. PDGF-BB and EGF peaked at 1 ng/ml with a 2.0 and a 2.5-fold increase respectively in the number of keratocytes migrating, whereas TGF-beta 1 reached a maximum response at 0.1 ng/ml, with a 1.7-fold increase. Chemotaxis reached an early plateau and remained constant at concentrations between 1 ng/ml and 100 ng/ml when stimulating with TGF-alpha (2.7-fold), bFGF (2.0-fold), aFGF (2.7-fold), and IGF-I (4.5-fold). Checkerboard analysis revealed that all growth factors were chemotactic agents for human keratocytes, except bFGF, which principally stimulated chemokinesis.

CONCLUSION

These in vitro results demonstrate that PDGF-BB, EGF, TGF-alpha, aFGF, IGF-I, and TGF-beta 1 increase keratocyte chemotaxis, and they may play an important role in the early recruitment of keratocytes to the corneal wound site in vivo.

Topography of corneal grafts before and after penetrating keratoplasty

PURPOSE

Refractive error after penetrating keratoplasty is a major clinical problem. The purpose of the present study was to investigate whether the topography of the donor cornea influence the topography of the graft after transplantation.

METHODS

Twenty-five donor corneas were measured with a video-keratograph (TMS-1): in situ and before and after organ culture. Clinical video-keratographic images of the transplanted grafts were subsequently obtained one week, 1, 3, 6, 12, and 24 months after surgery. The central spherical equivalent power and corresponding regular and irregular astigmatic powers were computed.

RESULTS

A statistically significant correlation between spherical equivalent central donor power and spherical equivalent central graft power after keratoplasty was found at all times up to two years after surgery. Only 13-50% of the variation in post-keratoplasty spherical graft power could, however, be explained by the donor graft power. Corresponding 95% confidence limits for prediction of post-keratoplasty power from donor graft power were approximately +/- 6.5 diopters. Post-keratoplasty regular or irregular corneal astigmatism did not correlate with astigmatism in the donor graft.

CONCLUSION

Corneal donor graft spherical equivalent power does influence the spherical equivalent corneal power after keratoplasty, especially during the first months after surgery. The dependency is, however, not very strong and until other determinants of post-keratoplasty corneal shape are known and controllable, 'power-typing' of donor corneas appears to be of limited clinical use.

Comparison of objective methods for quantifying the refractive effect of photo-astigmatic refractive keratectomy using the MEL-60 excimer laser

PURPOSE

To investigate the accuracy and precision of automated keratometry, automated refractometry, and computerized corneal topography in estimating the subjective refractive outcome of photo-astigmatic refractive keratectomy six months postoperatively.

METHODS

Photo-astigmatic refractive keratectomy (Aesculap-Meditec, MEL-60 Excimer Laser) was performed on 26 eyes with a preoperative myopia ranging from -4.0 to 7.6 dioptres, and a naturally occurring astigmatism from 0.75 to 5.0 dioptres. Six months postoperatively refractive outcome was evaluated by automated keratometry, automated refractometry (Nikon NRK-8000), computerized topography (TMS-1), and subjective refraction. Estimate errors were computed as the difference between the change in subjective refraction and the change in automated keratometry, automated refractometry, and surface topography, respectively. Astigmatic changes were evaluated by the second harmonic component in the Fourier series analysis.

RESULTS

Subjective spherical as well as cylindrical values were reduced significantly six months postoperatively. The estimate error (mean +/- one standard deviation) for automated keratometry was -1.26 +/- 0.72 dioptres for the spherical equivalent and -1.36 +/- 1.02 dioptres for the cylinder; for automated refractometry it was -0.78 +/- 0.91 dioptres for the spherical equivalent and -0.66 +/- 0.92 dioptres for the cylinder. The best estimates of subjective changes were obtained when the average of ring 2 and 3 of the topographic data was used: -0.15 +/- 0.82 dioptres for the spherical equivalent and -0.78 +/- 0.80 dioptres for the cylinder.

CONCLUSIONS

The computerized topographer with the Fourier analysis was superior to automated keratometry and automated refractometry in estimating the subjective spherical refractive outcome and comparable to automated refractometry in estimating the subjective cylinder refractive outcome after photo-astigmatic refractive keratectomy.

Persisting corneal oedema following intracapsular cataract extraction

PURPOSE

The purpose of this study was to reveal the frequency of persisting corneal oedema following intracapsular cataract extraction and at the same time to examine whether the survival rate after penetrating keratoplasty due to this diagnosis differs from the survival rate following penetrating keratoplasty due to primary Fuchs' endothelial dystrophy.

METHODS AND MATERIAL

A series of 2455 eyes underwent intracapsular cataract extraction between January 1, 1986 and December 31, 1988, at the Department of Ophthalmology, Arhus University Hospital. The medical files were examined to study the frequency of persisting corneal oedema. Patients with persisting corneal oedema were offered penetrating keratoplasty and the survival rate following this procedure was calculated.

RESULTS

The frequency of pseudophakic persisting corneal oedema was 5.3% in the group of patients who underwent intracapsular cataract extraction. The survival of the following corneal transplantation was 54% after 2 years of follow-up. This is a low survival rate compared to the survival rate in primary Fuchs' endothelial dystrophy, but there is a similarity to this disease in a development of a slowly progressive oedema in 17% compared to 13% in primary Fuchs' endothelial dystrophy.

CONCLUSION

5.3% of a group of patients who underwent intracapsular cataract extraction developed persisting corneal oedema within a 5 to 7-year follow-up period. When these patients underwent penetrating keratoplasty the survival rate of the graft was 54% after 2 years of follow-up.

Value of intraoperative keratometry in predicting outcome of radial keratotomy

PURPOSE

To investigate whether the immediate change in corneal power during radial keratotomy correlates with the long-term postoperative change in subjective refraction, and thereby being predictive for refractive outcome.

METHODS

Manual keratometry was performed on 45 consecutively operated eyes of 45 young persons with myopia of 5 dioptres and less and immediately after radial keratotomy. Automated keratometry and subjective spherical equivalent refraction were investigated during a follow-up period of 6 months and correlated to the intraoperative keratometric measurements.

RESULTS

On average, the majority of the change in corneal curvature after radial keratotomy took place within 1 min. There was no correlation between the intraoperative curvature change and the changes in curvature measured up to 6 months after surgery. There was a weak significant positive correlation between intraoperative curvature change and the change in subjective refraction at 6 months after surgery (R = 0.48, p < 0.01). The prediction error in estimating subjective refractive changes from intraoperative keratometry changes was, however, similar in patients who had bilateral radial keratotomy. Inclusion of such fellow-eye information together with the age of the patient in a multiple linear regression analysis increased the correlation coefficient from 0.48 to 0.75.

CONCLUSIONS

The change in central corneal curvature takes place within minutes after corneal incision. As a single parameter, intraoperative keratometry cannot be used for titrating surgery. Information from the results of first eye radial keratotomy surgery with intraoperative keratometry is, however, predictive for radial keratotomy in the second eye. These findings suggest that a large source to refractive variability after radial keratotomy is related to individual patient factors, such as corneal biomechanics and wound healing.

Graft survival and risk factors of penetrating keratoplasty for microbial keratitis

PURPOSE

To evaluate graft survival rates and prognostic factors in relation to penetrating keratoplasty for microbial keratitis.

METHODS

The records of 95 patients treated with penetrating keratoplasty for microbial keratitis during a twenty-year period were reviewed. Data were analysed by construction of survival curves using the Kaplan-Meier non parametric method.

RESULTS

The overall survival of a clear cornea was 72% after one year, 71% after two years and 52% after five years. A significantly lower survival rate (p<0.05) was found in the presence of preoperative local risk factors such as wear of contact lenses and trauma and in inflamed eyes. In contrast, systemic diseases like diabetes, cancer or rheumatoid arthritis did not affect survival and neither did recipient age nor the degree of vascularization of the eye. Male donor buttons showed superior survival compared to female ones (p < 0.05), while females seemed to constitute the best recipients. Recurrence rates of microbial keratitis postoperatively were 11%, 16% and 24% after one, two and five years, respectively. Corresponding graft rejection rates were 9%, 15% and 27%.

CONCLUSIONS

Patients suffering from microbial keratitis have a relatively high risk of graft failure. To improve the prognosis care should be taken to minimize local risk factors. Surgery should whenever possible be performed on quiet eyes. The unexpected finding of a better prognosis for male donor buttons might suggest the preferred use of male donors in patients suffering from microbial keratitis, but the observation needs further documentation.

Keratocyte migration and peptide growth factors: the effect of PDGF, bFGF, EGF, IGF-I, aFGF and TGF-beta on human keratocyte migration in a collagen gel

PURPOSE

Peptide growth factors are known accelerators of corneal wound healing, probably mediated through increased proliferation of the cells; however, information about their effect on keratocyte motility is lacking. The influence of peptide growth factors on keratocyte migratory activity was investigated, using the following growth factors: platelet derived growth factor (PDGF-BB), epidermal growth factor (EGF), acidic fibroblast growth factor (aFGF), basic fibroblast growth factor (bFGF), insulin-like growth factor-I (IGF-I) and transforming growth factor-beta-1 (TGF-beta 1).

METHODS

Keratocytes were seeded on gels of type 1 collagen, growth factor added, and the cells left to migrate for 72 hours. Subsequently, the number of keratocytes at the different levels in the collagen gel was evaluated by optically sectioning the gel at 20 microns, intervals, with an inverted phase contrast microscope.

RESULTS

PDGF, EGF and bFGF at 10 ng/ml, all increased the number of keratocytes at the different levels of the gel as compared to a non-stimulated control (p < 0.05 or p < 0.01, students t-test). TGF-beta proved to be a strong inhibitor of keratocyte migration, decreasing the number of keratocytes observed at every level in the gel (p < 0.05 and p < 0.01, students t-test), whereas no effect of IGF-I and aFGF was found. During the 72 hours of migration, no contraction of the collagen gels was observed. Autoradiography of histological sections of the gels showed that during the 72-hour period only TGF-beta and 10% fetal bovine serum induced an increase in keratocyte proliferation.

CONCLUSION

PDGF, EGF and bFGF increase keratocyte migration, independent of proliferation in a collagen gel invasion assay and might promote corneal wound healing, not only by increasing cell proliferation, but also through increased motility.

[Biomechanical study of corneal stability after photorefractive keratectomy]

BACKGROUND

Photorefraktive keratectomy (PRK) is the most frequent refractive surgical procedure worldwide. The central corneal thickness is reduced due to removal of the anterior stroma, including Bowman's layer, with a laser beam. This procedure results in considerable alterations of the corneal structure. What does this mean for the mechanical properties of the cornea?

METHODS

Intraocular pressure was increased via a 180 degrees tilt. Before and during this procedure, corneal topography was measured by photokeratoscopy. We examined 26 patients after PRK and 25 controls who had not undergone any surgical procedure.

RESULTS

The corneal center flattened by 0.038 +/- 0.05 dpt (P > 0.05) in the PRK patients and by 0.187 +/- 0.045 dpt (P < 0.05) in the control group. PRK patients within 1 year after operation showed a minimal central corneal steepening, whereas PRK patients after more than 1 year showed a reaction similar to that in normal corneas (P < 0.05).

CONCLUSION

Corneal stability is altered after PRK. After 1 year corneal stability seems to normalize due to stromal remodelling.

Significant effect of high-resolution HLA-DRB1 matching in high-risk corneal transplantation

The effect of HLA matching in corneal transplantation is still--after numerous of studies--disputable. We investigated the effect of DRB1 matching in high-risk cases with vascularization and/or retransplantation. Only class II antigens were matched because we were unable to obtain donor lymphocytes for HLA typing. Typing was performed on DNA isolated from the ocular tissues up to 24 hr after death. When this study was initiated, DNA-based methods had been developed only for class II typing. The first part of the study concerns 74 cases with at least 3 years of observation fully matched for 17 DRB1 specificities detected using restriction fragment-length polymorphism. This showed an improved long-term graft survival of 72% compared with 45% in a historical control group of 23 comparable cases. In the second part of the study, stored DNA samples from the restriction fragment-length polymorphism-matched donor-recipient pairs were subjected to retyping with a new method based on sequence-specific polymerase chain reaction. It was possible to split DRB1*01, *04, and *11 in 3, 14, and 5 alleles, respectively. The matching was then re-assigned taking all splits into account. This showed that 36 cases had at least one incompatibility, whereas 38 cases were fully compatible. The long-term graft survival rate was 79% in the matched group compared with only 59% in the mismatched group, which is significantly different at P=0.032. This retrospective, but blinded, randomized study is strong evidence for the effect of matching and may give scope for international collaboration to obtain completely matched corneas for this group of patients.

The effect of 193 nm excimer laser radiation on the human corneal endothelial cell density

The effect of 193 nm excimer laser radiation on human corneal endothelial cell density was examined. Fifty-five eyes from 35 patients underwent photorefractive keratectomy for myopia. Photomicrographs of the endothelium were taken a short time before the operation and on an average of 7 months postoperatively with a specular microscope. The average endothelial cell densities were preoperatively 3375 +/- 266 cell/mm2 (mean +/- SD) and postoperatively 3348 +/- 287 cells/mm2, corresponding to a fall of 27 cells/mm2 (N = 55). This fall in endothelial cell density was not statistically significant. A significant correlation between the change in cell density and age of the patient was found, with older patients losing more cells (N = 35, 2p < 0.05). The magnification of the specular microscope was found to change with corneal thickness. The importance of correcting the endothelial cell densities for corneal thickness is discussed.

Epithelial healing in the second eye after corneal abrasion

Corneal epithelial healing velocity was determined in patients admitted to excimer laser photo refractive keratectomy, by daily video planimetry of the denuded area until complete healing. The epithelial healing process was followed in fellow eyes with regard to intervals between surgery of the two eyes of 1 to 10 weeks. In cases where the fellow eye was treated at one week after the first eye, the lesions healed significantly faster in the second eye as compared to patients with longer delay between the two operations.

[Biomechanical study of corneal stability after radial keratotomy]

BACKGROUND

Radial Keratotomy is one of the most frequent refractive surgical procedures performed worldwide. It results in considerable alterations of the corneal structure. What does this mean for the mechanical properties of the cornea?

METHODS

Intraocular pressure was increased via a 180 degrees tilt. Before and during this procedure, corneal topography was measured by photokeratoscopy. We examined 36 patients after RK and 25 controls who had not undergone any surgical procedure.

RESULTS

The corneal center flattened by 0.523 +/- 0.054 dpt (p < 0.01) in the RK patients and by 0.187 +/- 0.045 dpt (p < 0.05) in the control group.

CONCLUSION

Even several years after radial keratotomy, corneal stability is still decreased.

Mechanical Stability of the Cornea After Radial Keratotomy and Photorefractive Keratectomy

BACKGROUND

Corneal refractive surgical procedures alter the shape and structure of the tissue, possibly compromising its mechanical stability.

METHODS

One or both eyes of 87 subjects were studied: 26 of these 87 had been treated for myopia by excimer laser ablation and 36 by radial keratotomy; 25 without previous corneal surgery functioned as controls. Corneal topography was evaluated by TMS-1 videophotokeratography before and after 180 degrees tilting of the patient, and the pressure-induced ring-wise changes in spherical equivalent power (axial power) were calculated. Changes in corneal shape also were evaluated by computing the instantaneous radius of curvature. The intraocular pressure was measured before and after tilting by a hand-held applanation tonometer.

RESULTS

The mean intraocular pressure increased from 13.9 +/- 2.3 mm Hg before tilting to 30.0 +/- 3.8 mm Hg during tilting. In the control eyes, the mean power of the central cornea during tilting decreased 0.187 +/- 0.045 diopters (D) (p < .05); in the excimer-laser-ablated eyes, 0.038 +/- 0.056 D (not statistically significant); and in those treated with radial keratotomy, 0.523 +/- 0.054 D (p < .01). After radial keratotomy, the cornea steepened outside the clear zone in response to pressure loading, whereas it did not change significantly in the laser-ablated or control eyes.

CONCLUSIONS

Pressure-induced deformation of normal and excimer laser-ablated human cornea is small, whereas radially incised corneas have significantly decreased mechanical stability.

[Diagnosis and treatment of conjunctivitis]

Conjunctivitis is a frequent reason for consulting a doctor. Most often treatment consists of antibiotics, even though sensitive bacteria are only rarely demonstrated. In our part of the world conjunctivitis is self-limiting, and it may be worth considering the effect of treatment, if any. With this in mind, diagnosis and differential diagnoses are reviewed and with regard to treatment distinctions are made between neonatal conjunctivitis (gonococcus, chlamydia, virus), conjunctivitis in children (symptoms of upper respiratory tract infections), and conjunctivitis in adults and the elderly (dry eyes, epiphora in ectropion).

Acute Tissue Deformation of the Human Cornea After Radial Keratotomy

PURPOSE

The regional deformation pattern of the cornea after radial keratotomy, which is essential for understanding the mode of action of the procedure, has not previously been studied in detail.

METHODS

Up to 90 tiny mercury droplets were placed from center to limbus on the epithelial and endothelial corneal surfaces of eight eviscerated human donor eyes with four radial keratotomies (depth 100% of central corneal thickness, 3.5-mm clear zone). From digital images obtained under pressure loads ranging from 2 to 100 mm Hg, the distances between the fixed droplets were measured with an accuracy of 1 micron. After transforming the data to polar coordinates, regional meridional and circumferential strain patterns were calculated. Regional meridional and circumferential radii of curvatures were calculated from corneal profile images obtained at different pressure loads before and after keratotomy.

RESULTS

Increasing the intraocular pressure from 2 to 100 mm Hg induced: an epithelial side wound gape of 44 mm; epithelial side circumferential tissue compression between incisions; considerable epithelial side meridional tissue elongation at and between incisions; little endothelial side circumferential strain across incisions; and little endothelial side meridional strain at and between incisions. The radial keratotomy induced 2.30 diopters (D) of central corneal flattening at an intraocular pressure of 2 mm Hg. The degree of central flattening correlated linearly with the amount of wound gape. In the physiological pressure range of the central cornea flattened 0.05 D for each millimeter-of-mercury increment in intraocular pressure. Pronounced meridional steepening was induced corresponding to the middle and peripheral parts of the keratotomy incisions.

CONCLUSIONS

Our study suggests that the peripheral "tissue addition" seen after radial keratotomy is a net result of wound gape and circumferential tissue compression. Local bending of intact stromal tissue below the incisions plays an important role for the generation of the wound gape at the corneal surface. These data may help verify finite-element computer models of the human cornea.

[Diagnosis and treatment of conjuncitivitis]

Conjunctivitis is a frequent reason for consulting a doctor. Most often treatment consist of antibiotics, even though sensitive bacteria are only rarely demonstrated. In our part of the world conjunctivitis is self-limiting, and it may be worth considering the effect of treatment, if any. With this in mind, diagnosis and differential diagnoses are reviewed, and with regard to treatment distinctions are made between neonatal conjunctivitis (gonococcus, chlamydia, virus), conjunctivitis in children (symptoms of upper respiratory tract infections), and conjunctivitis in adults and the elderly (dry eyes, epiphora in ectropion).

A three-dimensional study of the human corneal keratocyte density

The population of stromal keratocytes represents a rarely examined topic. In the present paper we investigated the three-dimensional distribution of keratocytes in human donor corneas. The keratocyte density was calculated from biochemical measurements of the DNA content in samples of the corneal (and scleral) stroma obtained from well-defined regions. The DNA content of the central stroma (0-2 mm from apex) had a mean (+/- SD) of 1.25 +/- 0.30 micrograms DNA/mg dry tissue weight, corresponding to a cellularity of 4.6 +/- 1.1 x 10(4) cells/mm3 (n = 13). Towards the corneal periphery, the cellularity gradually increased to a 60-70% higher cell density at limbus. In the central stroma, an anterior-posterior cell gradient was found with a 30% lower cellularity in the subendothelial region compared to the subepithelial stroma (n = 8). In the four main quadrants of the central stroma, a uniform cell density was found while the peripheral areas showed a 10% higher cellularity in the superior quadrant. A close intraindividual correlation was observed between data obtained from 40 paired corneas ('cornea 1' versus 'cornea 2'); the stromal cellularity within 0-3.75 mm from apex (r = 0.81), the stromal cellularity within 3.75-5.5 mm (r = 0.92), the stromal cellularity within 5.5-8.0 mm (r = 0.85), and the endothelial cell density (r = 0.84). However, within a given cornea no correlation was found between the density of endothelial cells and keratocytes. These data define normal values for the regional density of keratocytes in the human cornea.

Healing velocity of corneal epithelium evaluated by computer. The effect of topical steroid

To objective determine the area of corneal abrasion, a video camera was connected to a slit-lamp. The videosignal was digitized and analyzed by a computer program. The maximal horizontal and vertical diameters were measured as well as the total abraded area. The algorithms of calculating healing velocity of corneal epithelium are discussed, and this system was tested on patients treated for myopia with a 193 nm ArF excimer laser. It was shown that topical steroid application did not impair corneal epithelial healing velocity.

Effect of excimer laser keratectomy on the mechanical performance of the human cornea

Enucleated human eye globes were set-up for measurements of pressure (2-100 mmHg) induced tangential epithelial and endothelial side corneal strain, and for measurements of central corneal thickness and central radius of curvature. In one experimental group (N = 6), a shallow ablation (15-20 microns deep) removing Bowman's layer was performed in the central 7 mm diameter zone of the cornea. The fellow eye served as control (N = 6). In another experimental group (N = 6) a 70% deep keratectomy was performed in the central 7 mm diameter zone. The pressure induced central corneal strain was 5-10% higher in corneas without Bowman's layer compared with intact corneas. The epithelial side tangential corneal strain in eyes with a 70% deep keratectomy increased to twice as much as that of intact corneas, but the endothelial side strain was similar. In all groups of eyes Young's modulus of elasticity increased rapidly with the corneal stress level up to testing loads of 25 mmHg. At higher loads the degree of stress-stiffening was smaller. The differences in average corneal strain between the 3 groups could be explained by the induced changes in central corneal thickness, as there were no statistically significant differences in stress-normalized Young's modula of elasticity between the 3 groups. The central radius of curvature did not change significantly with increasing pressure in intact eyes or in eyes without Bowman's layer. In deep keratectomized corneas the corneal radius of curvature decreased approximately 1% when the intraocular pressure was increased from 2 to 100 mmHg.(ABSTRACT TRUNCATED AT 250 WORDS)

Recurrence and rejection rates following corneal transplantation for herpes simplex keratitis

Seventy-two penetrating primary keratoplasties for herpes simplex keratitis performed from 1970 to 1993 were reviewed. Postoperative follow-up periods ranged from 6 months to 16 years with 2 years median. Epithelial herpetic recurrence occurred in 25% of the transplants the first year and in 44% during the first 2 years. Primary allograft rejection was observed in 29% of the grafts the first year and in 46% during the first 2 years. Preoperative inflammation was a risk factor for preservation of a clear cornea (p < 0.10). The degree of corneal vascularization prior to operation did not influence the survival of the grafts. The overall one-year survival rate of a clear graft was 84% and the 2-year survival rate was 67%. Prophylactic antiviral treatment is discussed.

[Excimer laser therapy of recurrent corneal erosions]

Recurrent corneal erosions have been recognized as a clinical problem for many years. Many patients with erosions do not respond satisfactorily to the standard treatment. In this paper we present a study of treatment of 24 patients with recurrent corneal erosions with the excimer laser, where 75% of the patients reported the treatment as a success.

Corneal storage and complications related to grafting

This review covers the literature during the past year and follows up results published on corneal storage techniques and complications related to corneal grafting. It considers the recent progress and suggests new perspectives on the reconstituted or renovated human donor cornea. It might be possible to revive postmortem donor corneas with new cells, eg, epithelial, endothelial, or keratocytes, drawn from the future recipient or eventually with transgenetic multidonor cells. The future holds promise for the development of a new concept in corneal banking, where we leave the period of conservation and enter the era of donor cornea production.

Histopathological findings in failed human epikeratophakia lenticules

Six human epikeratophakia lenticules were removed 1 to 23 months after refractive keratoplasty for aphakia (n = 2) and myopia (n = 4). The myopic group included one epi-lenticule treated with ArF-excimer laser for hyperopia. Reasons for removal were epithelial defect (n = 4), edema of host cornea (n = 1), and overcorrection (n = 1). The epi-lenticule stroma showed centrally a regular fibrillar structure with a low keratocyte density. Electron microscopy (n = 1) revealed preserved cytoplasmic organelles and nuclear appearance. Mononuclear cells were absent. Polysaccharide was demonstrated in the stroma. Bowman's layer was normal without breaks. The epithelium had variable thickness. In the peripheral wound region stromal and epithelial irregularities were evident.

The keratocyte density of human donor corneas

The cellularity of the human corneal stroma has not been described in the literature. In the present study we calculated the density of keratocytes in human donor corneas using a new method for biochemical measurement of the stromal DNA content (sDNA). The DNA measurements were compared to morphological counts of the number of keratocyte nuclei per area (KNPA) obtained from histological sections. A significant correlation was found between the data achieved by the two methods (r = +0.52, p < 0.001, n = 46). No significant change in either sDNA or KNPA was found during 28 days of organ culture, and no influence of donor age, sex, or post mortem time was found on either sDNA or KNPA. Both sDNA and KNPA approximated a normal distribution with a mean sDNA of 1.10 +/- 0.25 micrograms DNA/mg dry tissue weight and an average KNPA of 200 +/- 53 nuclei/mm2 (n = 35). Between paired corneas the sDNA were closely correlated (r = +0.83, p < 0.005, n = 11 pairs) with an intra-individual variation of only 0.5%. Using the sDNA data, the keratocyte density in the central region of human donor corneas was calculated to be 129,000 +/- 29.000 per mg dry tissue weight (n = 35). Thus, when corneal grafting is performed (using a 7 mm trephine) an average of 818,000 +/- 186,000 donor keratocytes are transplanted. Assuming a uniform cellularity throughout the stroma, the average number of keratocytes was calculated to be 2,430.000 +/- 551,000 per human donor cornea.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term results with organ cultured, cryopreserved human corneal grafts. Re-examination of 17 patients

Seventeen organ cultured cryopreserved corneas were grafted in 1978-79. When published in 1982, 12 of the grafts (71%) were clear with an average thickness of 0.51 mm and an endothelial density of 1028 cells/mm2. A re-examination of these patients after 13 years is presented. Seven grafts (58%) were clear. Average CCT was 0.51 mm and endothelial cell density was 988 cells/mm2. Visual acuity was 0.4 or better. The morphology resembled that seen after 1 year with large, multinucleated cells. It is concluded that cryopreserved grafts show a fair long-term survival. Cryopreservation may still present a possibility in the establishment of a corneal bank with the perspective of supplying histocompatible donor material.

Differential diagnosis between granular corneal dystrophy Groenouw type I and paraproteinemic crystalline keratopathy

A case of corneal opacities in a leukemic patient with an M-component in the serum proteins is presented, and a comparison is made to patients with granular corneal dystrophy Groenouw type I. The corneal deposits associated with the two conditions may appear identical with slit-lamp biomicroscopy. Granular dystrophy patients, however, show a normal serum immunoglobulin pattern in contrast to patients with paraproteinemic crystalline keratopathy. The two entities can therefore be distinguished from each other by a serum electrophoresis.

The effect of topical steroid on postoperative corneal edema and endothelial cell loss after intracapsular cataract extraction

In a prospective study of 89 patients the postoperative corneal edema and endothelial cell count was studied after cataract extraction. A double blind investigation was performed as the patients during the first 6 postoperative days were treated with three different types of eye-drops: Maxidex, Pred-Forte 1% or placebo, all containing Benzalkonium Chloride 0.004%. The content of steroid in Maxidex and Pred-Forte was equivalent. We found no significant difference in estimates of endothelial cells in the three groups postoperatively. Corneal edema was less in the two groups treated with steroid. There was no significant difference between the two postoperative groups (p > 0.05) treated with Maxidex and Pred-Forte. The group treated with Pred-Forte showed significantly less postoperative corneal edema, calculated as the graphical area represented by the increase of central corneal thickness (CCT) after operation.

Excimer laser refractive keratectomy for high myopia. 6-month follow-up of patients treated bilaterally

Both eyes of twenty patients were treated for myopia with refractive keratectomy using an excimer laser (193 nm), and followed for six months. The 40 eyes were divided into Group I (22 eyes) with an attempted refraction change of 5-8 diopters; and Group I (18 eyes) with 9-12 diopters of attempted refraction change. In Group I the corrected visual acuity improved or was unchanged in 16/22 eyes. Two eyes with high preoperative corrected visual acuity had experienced a significant loss in corrected visual acuity after 6 months. In Group II, the corrected visual acuity decreased in 10/18 eyes, in 4 eyes significantly. Among the 40 eyes, 39 had a refraction change less than intended after 6 months. Overcorrection was seen in only 1 eye. In Group I, 20/22 eyes were corrected up to 2.5 diopters less than attempted. In Group II, 9/18 eyes were more than 2.5 diopters from the attempted correction. All eyes developed subepithelial opacification ('haze'), which, in spite of steroid treatment, was still present after 6 months. The haze was more severe in eyes treated with 9-12 diopters of attempted refraction change. The achieved refraction change in the two eyes of the same patient was found to be correlated, possibly due to an individual factor in corneal wound healing.

Excimer laser treatment of pterygium

Primary experience with the use of excimer laser in pterygium therapy is presented. Twenty-two pterygia (11 primary and 11 recurrent) were surgically removed using the bare-sclera technique followed by excimer laser ablation to smooth the corneal surface. As recurrence was observed in 20 eyes (91%) during the first year, supplementary excimer laser treatment of a pterygium does not seem to reduce the recurrence rate. The high recurrence rate in this series may to a certain extent reflect the surgical technique used (bare-sclera).