HLA types in corneal diseases

Evaluation of the results of HLA typing of 187 patients grouped into herpetic keratitis (37), non-herpetic keratitis (43), keratoconus (42), endothelial dystrophy (23), stromal dystrophy (13), lues (5), and injuries (24), failed to show convincing deviations in any of the groups from a normal control series (2900 persons). Yet, as for the herpes group, a rise in B5 must strongly be suspected. The data are presented and possible implications are discussed.

Continuous hypoxic culturing maintains activation of Notch and allows long-term propagation of human embryonic stem cells without spontaneous differentiation

OBJECTIVE

The maintenance of pluripotency of human embryonic stem cells (hESCs) requires a high efficiency of self-renewal. During in vitro propagation, however, hESCs have a propensity to differentiate spontaneously. In this study, we assessed the nature of hESC responses to hypoxic conditions.

MATERIALS AND METHODS

Human embryonic stem cells were grown in normoxic and hypoxic conditions, and the cells expressing Oct4 and stage-specific embryonic antigen-1 were identified by indirect immunofluorescence. The transcriptional expression of Nanog, Notch1, and Oct4 was determined by a real-time reverse transcription-polymerase chain reaction, and the inhibition of Notch-mediated signalling was achieved with a gamma-secretase inhibitor.

RESULTS

In contrast to culture at 21% oxygen, where the colonies displayed a marked degree of differentiation, we found that during exposure to 5% oxygen, the hESC colonies displayed a homogenous and flat morphology that was consistent with the presence of Oct4-positive phenotype, indicating no spontaneous differentiation. When cultured at 5% oxygen for either 4 weeks or up to 18 months, high levels of Nanog and Notch1 transcriptional expression were detected, albeit the expression was significantly lower during longer exposure. The suppression of differentiation was rapidly reversed on transfer of the hypoxic cultures to normoxic conditions. Looking into the molecular mechanisms of the maintenance of self-renewal at low oxygen tensions, we found that inhibition of Notch signalling fully abrogated the hypoxic induction of undifferentiated phenotype.

CONCLUSION

Our data, thus, indicate that hypoxic exposure has the capacity to sustain long-term self-renewal of hESCs and that this effect is mediated through activation of Notch.

Evaluation of potential organ culture media for eye banking using a human corneal endothelial cell growth assay

BACKGROUND

To evaluate the ability of different commercially available cell culture media to induce proliferation and morphological changes in primary cultures of human corneal endothelial cells (HCEC). This screening model was used in an attempt to establish a rational basis for the development of well-defined, serum-free preservation media for long-term organ culture of human donor corneas.

METHODS

A total of 11 different culture media enriched with 0%, 2%, 5%, and 10% fetal calf serum (FCS) were compared. The test media were divided into three groups: Group 1: Media based on minimal essential medium (MEM), currently used for long-term corneal organ culture in European eye banks; Group 2: F99-based media, enriched for growth of corneal endothelial cells at serum-reduced conditions; and Group 3: Media designed for growth of special cell types or for short-term corneal organ culture. The growth-promoting capacity of each test medium was quantified using an HCEC proliferation assay, whereas changes in cell morphology were evaluated by phase-contrast microscopy.

RESULTS

The morphological characteristics of HCEC were best maintained in the group of F99-based media, which also induced the highest level of cell proliferation under serum-reduced conditions. Specifically, the medium F99-Sr (F99 enriched with ascorbic acid, insulin, bFGF, transferrin, selenium, and lipids) induced a two- to three-fold higher HCEC density at both 0% and 2% FCS when compared to all other test media, and it also maintained the most endothelial cell-like morphology. Also, at higher serum concentrations (5% and 10% FCS), the cell growth was most prominent in F99-Sr, as well as in the medium SFM that originally was designed for serum-free growth of vascular endothelial cells.

CONCLUSION

This study suggests that the media F99-Sr and SFM should be further tested and refined as potential new storage solutions for long-term corneal organ culture at physiological temperatures.

Evaluation of potential organ culture media for eye banking using human donor corneas

AIM

To evaluate the ability of different commercially available cell culture solutions to preserve human donor corneas during 3 weeks of "closed system" organ culture at physiological temperature. This screening was performed in an attempt to establish a rational basis for the development of a serum-free organ culture medium for eye banking.

METHODS

72 normal human donor corneas were organ cultured for 21 days at 31 degrees C in eight different test media (nine corneas in each group). The basic culture solutions included: minimal essential medium (MEM), MEM with stabilised L-glutamine, M199, DIF-1000, SFM, F99, and F99 with ascorbic acid, insulin, bFGF, transferrin, selenium, and lipids (termed F99-Sr). All media were supplemented with 2% fetal calf serum (FCS), except for MEM, which was also studied at 8% FCS. The evaluation parameters included: (1) the endothelial cell loss as evaluated using trypan blue staining; (2) the ability of keratocytes and endothelial cells to incorporate tritiated uridine into RNA as evaluated using autoradiography and digital image analysis; (3) the leakage of immunogenic keratan sulphate as assessed using ELISA; and (4) changes in storage medium pH, glucose, and lactate content.

RESULTS

SFM induced the lowest endothelial cell loss of 14% (SD 2%) and the highest RNA synthesis rates of all test solutions supplemented with 2% FCS. Corneas stored in SFM also showed the least leakage of keratan sulphate and the highest glucose consumption and lactate production. In five media (MEM with 2% FCS, MEM with stabilised L-glutamine, M199, F99, and F99-Sr), comparable and intermediate potentials for organ culture were observed with endothelial cell loss of 16-19%. By contrast, 29% (4%) of the endothelium was lost after storage in DIF-1000. Interestingly, the use of 8% FCS (in MEM) had a marked protective effect on the endothelium, which showed the highest RNA synthetic activity combined with a cell loss of only 11% (4%), compared with 19% (6%) at 2% FCS (p<0.05).

CONCLUSION

Among the present test solutions, SFM appears to be the most prominent candidate for a new corneal organ culture medium and should be further tested and possibly refined to effectively substitute serum addition.

Treatment of post-keratoplasty astigmatism by topography supported customized laser ablation

PURPOSE

To evaluate the clinical and optical efficiency of topography modulated customized corneal ablations for irregular corneal astigmatism.

MATERIAL & METHODS

Sixteen eyes of 16 patients with iatrogenic corneal astigmatism (post keratoplasty) were consecutively included. Based on preoperative corneal topographic measurements height deviations from a spherical corneal shape were calculated and transferred to a flying-spot excimer laser. Photo-refractive keratectomy of the topographic irregularities was then performed. Clinical and optical efficiency was evaluated by best corrected visual acuity and by computation of corneal wavefront aberrations before and up to one year after treatment. Wavefront aberrations were decomposed by Zernike polynomial analysis.

RESULTS

Before treatment the average best-corrected visual acuity was 0.23. Three and 12 months after PRK the average best-corrected visual acuity had increased to 0.37 (p<0.05) and 0.45 (p<0.05), respectively. Corneal wavefront aberrations (root-mean-square) were 3.35 before surgery and 1.88 (p<0.05) and 1.51 (p<0.05) at three and 12 months after treatment. Zernike polynomial decomposition of the wavefront aberrations revealed that regular corneal astigmatism was the most important aberration component before and after surgery. Regular astigmatism was significantly decreased by the procedure, whereas coma, spherical aberrations, and higher-order aberrations were not reduced significantly.

CONCLUSION

Topography modulated photorefractive keratectomy of highly astigmatic corneal grafts can improve best corrected visual acuity and reduce corneal wavefront aberrations. Even in apparently irregular topographic astigmatism, regular astigmatic wavefront aberration may be the most important contributor to wavefront errors.

Human lens thioltransferase: cloning, purification, and function

PURPOSE

To clone the human lens thioltransferase (TTase) gene and to purify, characterize and study the possible function of the recombinant human lens thioltransferase (RHLT).

METHODS

The human lens TTase gene was cloned by using RT-PCR and verified by sequence and RNase protection assay. TTase overexpressed in Escherichia coli was isolated and purified to homogeneity by column chromatography and identified by Western blot analysis. The activity was assayed with a synthetic substrate hydroxyethyl disulfide. Its function in dethiolating and reactivating other key metabolic enzymes was studied by using pure glutathione S:-transferase (GST) and glutathione peroxidase (GPx) from commercial source and also with the cell extract of rabbit lens epithelial cells preexposed to H2O2.

RESULTS

The cloned human lens TTase gene showed identical sequence to the TTase gene from other human tissues. The RNase protection assay displayed a single transcript from the total RNA of human lens epithelial cells. The purified RHLT had a molecular weight of 11.8 kDa and reacted positively with anti-pig liver TTase. It displayed similar structural, functional, and kinetic characteristics to those of TTases from other sources. It was shown that RHLT effectively regenerated the activities of GST and GPx, after each was inactivated by S-thiolation with cystine in vitro. Furthermore, RHLT was able to restore the activity of the oxidatively inactivated glyceraldehyde-3-phosphate dehydrogenase (G-3PD) in H2O2-exposed rabbit lens epithelial cells.

CONCLUSIONS

The human lens TTase gene has been cloned for the first time. Its gene product showed the characteristics which support our speculation that TTase may play a major role in maintaining the homeostasis of lens protein thiols thus protecting against oxidative stress.

Stability of graft refractive power after penetrating keratoplasty

PURPOSE

Patients needing penetrating keratoplasty (PK) and cataract extraction with intraocular lens (IOL) implantation may be handled with a single triple procedure or a two-stage procedure with initial keratoplasty and cataract surgery in a later session. The latter approach is considered more safe by some surgeons and allows adjustment of the IOL power to the power of the actual corneal graft. The purpose of this study was to estimate the optimal timing of cataract surgery with IOL implantation by studying the refractive stability of 8 mm penetrating keratoplasty grafts.

METHODS

Penetrating keratoplasty (8.0 mm graft and recipient bed) was performed in 28 eyes of 28 patients. Corneal topography (TMS-1) was studied at 1, 2, 3, 6, and 12 months after surgery and after suture removal (30 months). The central spherical equivalent graft power was computed from the topographical data (rings 2 through 4).

RESULTS

On average, the spherical equivalent graft power was stable from one month after surgery up to suture removal (range: 41.9 to 42.7 diopters). After suture removal the graft steepened slightly (0.7 diopters). Corneal refractive power of single grafts fluctuated considerably over time. The standard deviation on time-dependent changes in graft power was from 3 months efter PK smaller than the standard deviation on the graft powers at 12 months.

CONCLUSION

The average central spherical equivalent power of an 8.0 mm donor graft in an 8.0 mm recipient bed was stable from one month after penetrating keratoplasty until suture removal. A two-stage procedure with cataract surgery performed 3 months after PK can, compared to the triple procedure, reduce postoperative ametropia at 12 months if graft topography is taken into consideration at the time of cataract surgery. We recommend that cataract surgery with IOL implantation takes place from 3 months after penetrating keratoplasty.

[Surgery for nearsightedness]

Myopia can today be reduced or eliminated by refractive surgery. Excimer laser surgery of the cornea by surface sculpturing (photorefractive keratectomy) or intrastromal tissue removal (LASIK) are the most widely used techniques, although implantation of intra corneal ring segments for low myopia also appears promising. Treatment of high myopia (> 10 diopters) is still difficult although epikeratoplasty or phakic IOL implantation are present possibilities. The perfect surgery for myopia remains to be developed, but the existing techniques will without doubt be further optimised. In 10 years time, supra normal visual acuity may even be obtained when surgical, optical, and biological variables can be described and controlled in each individual undergoing refractive surgery.

Refractive results of radial keratotomy: a ten-year retrospective study

PURPOSE

To investigate the long-term effects and stability of refraction after radial keratotomy procedure.

METHODS

Radial keratotomy was performed on 123 persons to reduce myopia (range: -1 to -13 diopters) in 1986 to 1989. A mean of 11.5 years later (range 10 to 13), 61 of these patients with 102 eyes underwent a standardised refractive examination where subjective spherical equivalent refraction was measured and compared to the preoperative and the one month postoperative refractive measurement collected from the patients records.

RESULTS

There was a reduction in spherical equivalent from an average of -5.46 diopters (SD 2.38) preoperatively to -2.32 diopters (SD 1.96) 11.5 years postoperatively. The mean change in direction of myopia between 1 month and 11.5 years postoperatively was 0.17 diopters (SD 1.18). This change was not statistically significant. From 1 month to 11.5 years, 10 of the eyes had developed more than 1 diopter hyperopia, and 20% more than 1 diopter myopia. When asked directly, all patients were satisfied with the result of their operation in general; 2 patients still complained of glare.

CONCLUSION

No significant changes in refraction were found between 1 month and 11.5 years after radial keratotomy. Previously reported long-term studies on this field have found a trend toward progressive hyperopia. No evidence of such change can be supported by this study.

Grafting of the posterior cornea. Description of a new technique with 12-month clinical results

PURPOSE

To describe the technique of grafting only the posterior cornea and to report 12-month clinical results.

METHOD

A two-layer technique with an anterior recipient flap created by a microkeratome and a posterior penetrating donor graft allows for a watertight wound closure and at the same time a peroperative correction of astigmatism. Four eyes (3 patients) were followed for 12 months.

RESULTS

The surgical technique could be completed in all cases without complications. The postoperative course was uneventful. The intrastromal absorbable sutures disappeared spontaneously and completely. Graft thickness showed the expected 6-month minimum while recipient flap thickness remained constant. After 1 year endothelial cell densities were 1200-2300 cells/mm2. Confocal microscopy showed activated keratocytes in the flap and quiescent keratocytes in the donor tissue by one year. The anterior chamber depth was normal in all cases. The optical quality of the cornea was studied by automatic keratometry and keratoscopy (TMS). The obtained optical properties were not optimal.

CONCLUSIONS

The developed novel technique gives a better wound closure and a complication free postoperative course. It may allow for better control of postoperative astigmatism. In order to disseminate the use of the technique, eyebanks should supply posterior corneas to the surgeon.