Immunocytochemical localization of basic fibroblast growth factor and glial fibrillary acidic protein after laser photocoagulation in the Royal College of Surgeons rat

PURPOSE

Argon laser photocoagulation slows photoreceptor degeneration in the Royal College of Surgeons (RCS) rat, as does intravitreal injection of basic fibroblast growth factor (bFGF). We hypothesize that up-regulation of retinal bFGF is a consequence of laser lesioning in RCS rats. Therefore, we examined the localization of bFGF after laser and correlated this with Mailer cell glial fibrillary acidic protein (GFAP) expression, which is known to increase after injury.

METHODS

A total of 34 RCS rats at postnatal day 23 were anaesthetized (ketamine 40 mg/kg) and their retinas were irradiated with a grid pattern of 40 non-overlapping argon green lesions with a power of 120 mW for 0.2 s using a 50 microm spot size. At 0, 6, 12, 24 and 48 h and 7, 14 and 21 days post-lesion, rats were anaesthetized and their eyes were enucleated and cryostat sectioned and the sections were processed using either an antibody to bFGF or GFAP using the standard avidin-biotinylated peroxidase complex method. Five age-matched RCS rats without laser lesions served as controls.

RESULTS

Basic fibroblast growth factor immunoreactivity (IR) was normally located within cells in the ganglion cell layer inner nuclear layer and in retinal pigment epithelium cells and in the extracellular matrix/cell membranes of the outer nuclear layer (ONL). In lasered retinas, there was elevated bFGF-IR in the coagulated outer segments for the first 24 h. Retinal blood vessels/Müller cells/astrocytes were moderately labelled in and near each lesion immediately after lesion and became more intense after 48 h and persisted for at least 21 days. There was an elevation of bFGF-IR in the ONL on the lesion flanks at 14 days. Muller cell GFAP-IR was first detected at 6 h post-lesion and spread for a considerable distance beyond the lesion site. At 7 and 14 days, Müller cells at the lesion site had sprouted, while those on the flanks were still GFAP-IR.

CONCLUSIONS

Following laser lesion there was an increase in bFGF at the lesion core only for the first 24 h. However, elevated levels of bFGF were observed in the ONL at 14 days, which extended into the lesion flanks for a similar distance to that over which increased photoreceptor survival is found. These results provide support for the hypothesis that laser lesions induce bFGF and this may be the mechanism whereby photoreceptors are spared. Müller cell activation is consistent with growth factor stimulation, but was more widespread than the bFGF changes in ONL. However, blood vessel labelling was similarly widespread and so the responses may be linked between Müller cell GFAP reaction and blood vessel bFGF localization after laser lesions.

Assessment of anticollagenase treatments after insertion of a keratoprosthetic material in the rabbit cornea

PURPOSE

This study was performed to evaluate the enzyme production in response to implantation of the hydrogel material used in the experimental Chirila keratoprosthesis (KPro) and to assess the effects of five topical drugs on enzyme production and activity. KPros may be extruded from the cornea as a result of tissue melting, a process that involves excessive enzyme activity. To reduce the possibility of implant loss for the hydrogel Chirila KPro, a number of antiinflammatory drugs that have been used to treat other corneal melting conditions were investigated for their effect on initial collagenase activity after the implantation of KPro material into the rabbit cornea.

METHODS

Poly(2-hydroxyethyl methacrylate) sponge pieces were implanted into rabbit corneas. Prednisolone, tetracycline, medroxyprogesterone, acetylcysteine, and sodium citrate were assessed for effects on gelatinolytic activity and stromal collagenase [matrix metalloprotease-1 (MMP-1)] production in vivo and in vitro by using zymography and Western blotting techniques.

RESULTS

Whereas all five anticollagenase drugs were effective in reducing gelatinolytic activity in vitro, many were ineffective in vivo. However, medroxyprogesterone caused a reduction of gelatinolytic activity in vivo. The amount of MMP-1, as measured by immunoblotting, also was reduced by medroxyprogesterone treatment when compared with untreated controls. An increase in the apparent molecular weight of MMP-1 in operated corneas appears to be the result of the association of MMP-1 with collagen fragments resulting from the surgical trauma.

CONCLUSION

This study indicates that topical medroxyprogesterone may be a useful adjunctive therapy after prosthokeratoplasty.

Clinical results of implantation of the Chirila keratoprosthesis in rabbits

AIMS/BACKGROUND

An ideal keratoprosthesis (KPro) would closely resemble a donor corneal button in terms of its surgical handling, optics, and capacity to heal with host tissue in order to avoid many of the complications associated with the KPros which are currently in clinical use. This study was carried out to assess the long term clinical outcomes on implantation of the core and skirt poly(2-hydroxyethyl methacrylate) KPro in animals.

METHODS

20 KPros were made and implanted as full thickness corneal replacements into rabbits and followed for up to 21 months to date.

RESULTS

80% of the prostheses have been retained, with a low incidence of complications such as cataract, glaucoma, and retroprosthetic membrane formation which are frequently associated with KPro surgery.

CONCLUSIONS

KPros of this type may offer promise in the treatment of patients for whom penetrating keratoplasty with donor material carries a poor prognosis. Refinement of the KPro and further animal trials, including implantation into abnormal corneas, are however mandatory before human implantation could be planned.

Keratoprostheses: advancing toward a true artificial cornea

Keratoprosthesis surgery is carried out in very few centers. Elaborate surgical techniques and high complication rates limit the application of currently available keratoprostheses (KPros). However, the clinical need for an alternative to donor tissue has sparked considerable research interest in the development of new KPros. This paper charts the evolution of KPros from the earliest devices to those currently used, describes their drawbacks and discusses the specifications of an ideal device. Recent research focuses upon the use of porous polymers as the skirt component of core-and-skirt KPros in order to obtain improved biological integration of the prosthetic material. Developments in biomaterials technology make a KPro analogous to a donor corneal button an increasingly realistic goal. However, two particular problems still need to be addressed. First, it must be demonstrated that secure long-term fixation that is able to withstand trauma is achievable in a full-thickness artificial cornea. Second, an ideal artificial cornea for a wet eye requires an epithelialized surface, and this has yet to be achieved.

Modulation of cathepsin D activity in retinal pigment epithelial cells

This project used retinal pigment epithelial (RPE) cells to investigate the effects of up- and down-regulation of cathepsin D expression on the processing of cathepsin D and on the normal phagocytic and digestive function of these cells. RPE cells were transfected with a pHbetaApr-1-neo vector construct carrying the full-length sequence of the translated region of human cathepsin D in sense and antisense directions. Transfected cells were characterized for the presence and expression of the transgene by PCR amplification using transgene-specific primers. Total aspartic proteinase activity present in transformed RPE cells was measured by an enzyme assay using haemoglobin as substrate. Flow cytometry was used to quantify phagocytosis of fluorescein isothiocyanate-labelled rod outer segments (ROS), and lysosomal digestion of ROS was monitored by immunofluorescence. A 435 bp fragment was present in RPE cells carrying the cathepsin D transgene in sense and antisense orientations after PCR amplification. Expression of both 52 kDa procathepsin D and 34 kDa active cathepsin D was significantly up-regulated in sense cathepsin D-transfected RPE cells and down-regulated in RPE cells transfected with antisense cathepsin D. No other forms of cathepsin D were detected in the transfected cells, suggesting that, if pseudo-cathepsin D exists in RPE cells in vivo, it requires the presence of unknown specific regulatory elements. The up- and down-regulation of cathepsin D expression was further confirmed by enzyme assay. Transfected cells retained their phagocytosing ability after ROS challenge and maintained their ability to process ROS. The processing of ROS was significantly slower in RPE cells transfected with antisense than control vector or in sense-cathepsin D-transfected cells. These results demonstrate that cathepsin D is a major proteolytic enzyme participating in the lysosomal digestion of photoreceptor outer segments.

Keratoprosthesis results in animals: an update

BACKGROUND

The report presented is an update on continuing development work on modified PHEMA core-and-shirt KPros in animals.

METHODS

Two variations (improved wet-eye, and dry-eye) of a prototype core-and-skirt Chirila KPro are described. The clinical success rate on implantation of these versions of the Chirila KPro was assessed.

RESULTS

It was found that a significant improvement in retention rate was shown in the improved model but that the dry-eye model failed early in two of the three implanted.

CONCLUSIONS

The significance of the improved strength and the reasons for disappointing results with the early dry-eye KPros are discussed. Ongoing work is briefly outlined.

Retinal artery and vein pressures in the dog and their relationship to aortic, intraocular, and cerebrospinal fluid pressures

The relationship between retinal arterial (Pra) and aortic (Pa) pressures is unknown, and the relationship between retinal vein (Prv) pressure and intraocular pressure (IOP) is not clear. Also unclear is the effect of cerebrospinal fluid pressure (CSFp) upon retinal venous pressure. We aimed to measure the relationships among Pra, Prv, Pa, IOP, and CSFp. Dogs were anesthetized while IOP, CSFp, and Pa were monitored. Pipettes with 2.5-micron diameter tips, connected to a servonulling pressure transducer, were used to record pressures from the retinal arteries and veins. Across a range of IOP (16-22 mmHg), CSFp (0-21 mmHg), and Pa (23-195 mmHg) the Pra = 0.72 Pa + 4.3 (r = 0.99, n = 61, P < 0.01), which suggests that the relationship between Pra and Pa is linear over a broad range of systemic blood pressures. The correlation coefficient between Prv and IOP was greater than 0.96 (P < 0.01) at all venous sites and whether IOP was greater than or less than CSFp. The transmural pressure varied along the retinal vein from 1.3 +/- 0.3 mmHg (+/-95% CI, n = 30) at 1 disk diameter from the optic disk rim to 0.3 +/- 0.2 mmHg (n = 66) at the optic disk, with a 0.9-mmHg/mm pressure gradient. These are the first measurements demonstrating a retinal vein transmural pressure close to zero.

Histologic evaluation during healing of hydrogel core-and-skirt keratoprostheses in the rabbit eye

PURPOSE

We developed two models that are modifications of our original poly(2-hydroxyethyl methacrylate) (PHEMA) core-and-skirt keratoprosthesis. In these keratoprostheses, the mechanical strength of the skirt has been considerably increased with divinyl glycol (DVG) as a cross-linking agent during polymerization. In one (KPro I), methyl methacrylate (MMA) was added as comonomer to increase cell adhesion, and in the other (KPro II), HEMA was polymerized with DVG without comonomer. The aim of this study was to evaluate the process of healing and biocolonization and to ascertain whether KPro I demonstrates better ingrowth than the mechanically stronger KPro II, after implantation in rabbit eyes.

METHODS

Ten rabbits were used for each model and studied at five predetermined end points up to 26 weeks. The device was implanted as a full-thickness keratoprosthesis covered with a conjunctival flap.

RESULTS

Neither prosthesis demonstrated extrusion or retroprosthetic membrane formation. There was no significant difference between the two types of prosthesis with respect to tissue ingrowth and surrounding tissue melting. Histologically, inflammation was not severe, but calcification was seen in most specimens. Evidence of biodegradation of the prosthesis also was seen.

CONCLUSION

In our original keratoprosthesis, fibrovascular invasion had occurred into the prosthetic skirt, but wound dehiscence and low mechanical strength resulted in an unfavorable outcome. In this series, the mechanical properties were improved, and KPro II was stronger than KPro I. Therefore KPro II would be the preferred polymer combination for surgical manipulation. However, biodegradation and calcification require further investigation into the degree and significance of these adverse reactions.

Effect of crosslinked poly(1-vinyl-2-pyrrolidinone) gels on cell growth in static cell cultures

Poly(1-vinyl-2-pyrrolidinone) (PVP) and copolymers of 1-vinyl-2-pyrrolidinone are insoluble in water when crosslinked but they can absorb very large amounts of water to become syringe-injectable hydrogels. Such gels have been investigated recently as potential substitutes for the vitreous humour in the eye. In this study, during the cytotoxic evaluation by sulforhodamine B colorimetric assay of variously crosslinked PVP gels, it was found that many of them showed protective/growth promoting effects on 3T3 mouse fibroblasts in static cultures, a phenomenon encountered previously only with aqueous solutions of a limited number of natural or synthetic polymers. Particularly, the gels crosslinked with diethylene glycol dimethacrylate (DEGDMA) induced a significant enhancement of cell proliferation, especially in serum-free cultures. No correlation between this effect and the essential gel properties (chemical composition, viscoelasticity and equilibrium water content) could be established. The study demonstrated that crosslinked PVP hydrogels showed a serum-like growth promoting effect on an anchorage-dependent cell line, which may be due to physical protection, inability of the insoluble gels to penetrate cell membranes, and their ability to mimic the extracellular matrix.

Dynamics of gene transfer to retinal pigment epithelium

PURPOSE

To examine the nature and dynamics of gene transfer to human retinal pigment epithelium (RPE) using an adenoviral vector and adjuvants that may enhance the uptake of recombinant adenoviruses.

METHODS

Human RPE cultures (HRPE7) were transfected in vitro with varying concentrations (4, 20, 40, 120, and 200 pfu/microliter) and for varying periods (1, 2, 4, 16, 24, 48, and 72 hours) with a replication-deficient adenovirus (Ad.RSV. beta gal) containing the bacterial beta-galactosidase transgene (beta gal). The expression of beta gal was monitored by counting after X gal staining. The transgene expression profiles were compared to those of human F2000 fibroblasts under the same conditions. The adjuvant effect of sodium hyaluronate (HA) on the expression of beta gal was tested in F2000 and early and late passage human RPE cells for differing concentrations of HA, viral titers, and incubation times. Immunofluorescent cytochemistry was carried on HRPE7 and F2000 cells for the HA receptors, homing receptor CD44 (CD44), intercellular adhesion molecule 1 (ICAM-1), and the receptor for hyaluronan mediated motility (RHAMM).

RESULTS

The number of HRPE7 and F2000 cells expressing the adenoviral transgene increased consistently with increasing incubation time and viral titer. There was a higher uptake of Ad.RSV. beta gal in HRPE7 cells compared to the F2000 fibroblasts under the same conditions. There was an increase of 28.1% and 41.4% in the number of RPE7 cells expressing adenoviral transgene and 16.2% and 15.8% F2000 fibroblast cells expressing the adenoviral transgene in the presence of 0.001% and 0.005% HA, respectively. Significant adjuvant effects on transgene expression also were shown in HRPE51 cells. It appears that the effects of increasing viral titer, length of incubation, and the presence of HA on transgene expression are at least additive. The appearance of CD44 and ICAM receptors on RPE7 and F2000 cells and RHAMM receptors on F2000 cells was similar. The RHAMM receptors in HRPE7 cells, however, were shown preferentially over the nucleus.

CONCLUSIONS

On the basis of these results, the authors propose that adenovirus transgene expression increases with increasing incubation time and viral titer in cell culture. The rate of increase of expression differs between human RPE cells and the F2000 fibroblast cells, which may offer a targeting opportunity. The authors propose that the use of HA can offer both an adjuvant effect and a targeting advantage in terms of transferring adenoviral transgenes to human RPE in culture.

Polymers of 1-vinyl-2-pyrrolidinone as potential vitreous substitutes: physical selection

More than 300 polymers of 1-vinyl-2-pyrrolidinone (VP) were synthesized, subjected to hydration, and characterized with the aim to select the most suitable materials as potential artificial substitutes for the vitreous body of the eye. The materials include cross-linked homopolymers, uncross-linked copolymers of VP with 2-hydroxyethyl methacrylate (HEMA), and cross-linked copolymers VP/HEMA. Five different cross-linking agents, both hydrophobic and hydrophilic, were used in this study. The resulting hydrogels, with equilibrium water contents ranging between 66.5 and 99.1%, were first subjected to a selection based on their physical behavior during manipulation, after which only the transparent, viscoelastic gels were further considered. Subsequent injectability and visual acuity tests, as well as the evaluation of light transmission characteristics, reduced further the number of potential candidates for vitreous substitution to only thirteen hydrogels. An eliminatory strategy based on physical properties of the potential vitreous substitutes is essential in order to avoid unnecessary sacrifice of experimental animals for in vivo assessment.

A simple flow cytometric technique to quantify rod outer segment phagocytosis in cultured retinal pigment epithelial cells

PURPOSE

The primary aim of this study was to develop and characterize a simple flow cytometric method of quantifying rod outer segment (ROS) phagocytosis in cultured retinal pigment epithelial (RPE) cells. A secondary aim was to compare the kinetics of ROS phagocytosis in an immortal human RPE cell line with untransformed human RPE cells.

METHODS

Flow cytometry was performed on RPE cells that had been challenged with fluorescein isothiocyanate-labeled ROS (FITC-ROS) and phagocytosis was calculated by subtracting background cellular autofluorescence.

RESULTS

Non-specific uptake of fluorescent label was negligible and RPE cells phagocytosed FITC-ROS and unlabeled ROS with equal efficacy. The kinetics of FITC-ROS phagocytosis in the D407 RPE cell line differed from early passage untransformed human RPE cultures. FITC-ROS phagocytosis proceeded at a fairly linear rate for the first 12 h in the 3 human cell cultures studied, but was rapid for the first 3 h before slowing in the D407 cells. Within all cell populations, there was a heterogeneity of phagocytic activity which varied with time.

CONCLUSIONS

This automated technique for measuring phagocytosis is rapid, simple, highly accurate, avoids radiation hazards, and permits study of heterogeneity within cell populations. The biochemistry, physiology and pathophysiology of the interactions between retinal pigment epithelial (RPE) cells and photoreceptors continue to be areas of considerable research interest (1, 2, 3). Vital to such work is the ability to accurately quantify rod outer segment (ROS) phagocytosis by RPE cells. Current in vitro techniques of measuring ROS phagocytosis use either automated or manual methods to count phagosomes. While manual counting techniques offer the advantage of visual quality control, they are highly labor intensive, there is a practical limitation to the number of phagosomes that can be counted, and measurements suffer from relatively large standard errors (3). Automated methods include scintillation counting and flow cytometry. Problems with radiolabels include radiation hazards, nonspecific radiolabel uptake, and limited visual control (3). Flow cytometry, on the other hand, circumvents nearly all of these problems and may prove to be the optimal phagocytosis assay.

Keratoprosthesis: preliminary results of an artificial corneal button as a full-thickness implant in the rabbit model

PURPOSE

To develop a prototype artificial cornea and evaluate it in the rabbit model.

METHODS

Hydrogel core-and-skirt keratoprostheses were made and were inserted as full-thickness implants covered with conjunctival flaps in the right eyes of eight rabbits.

RESULTS

Peroperative complications related to inadequate mechanical strength led to failure in the early postoperative period in three animals, one was euthanased for an unrelated reason and the remaining four have been successful for up to 16 weeks' follow-up.

CONCLUSIONS

Full-thickness implantation of an artificial cornea, analogous to penetrating keratoplasty, has been achieved in the rabbit model. Histological findings confirm that integration of the prosthesis with host tissue occurs. The main complications encountered in this preliminary series were related to inadequate strength of the sponge skirt of this prototype device. Work in our laboratories is now concentrated upon improving the mechanical qualities of the hydrogel skirt and on the enhancement of biointegration.

Correlation between autofluorescent debris accumulation and the presence of partially processed forms of cathepsin D in cultured retinal pigment epithelial cells challenged with rod outer segments

The purpose of the present study was to investigate the accumulation of rod outer segment (ROS)-derived debris in cultured human retinal pigment epithelial cells (RPE). The RPE cell layer is responsible for the phagocytosis and digestion of photoreceptor outer segments. Due to the immense volume of photoreceptor-derived material processed by the RPE cells, even minor changes in the efficiency of ROS processing may cause the accumulation of lipofuscin and photoreceptor derived debris. In this work, 17 RPE cultures were established from the globes of eye bank donors whose ages ranged from 18 to 79 years. Third passage cultures were challenged with bovine ROS and the accumulation of an autofluorescent debris was quantified using a flow cytometer. It was demonstrated that ROS challenge greatly increased the rate of autofluorescent debris accumulation. The accumulation of autofluorescent debris varied significantly from culture to culture. This variation was independent of the phagocytosing capacity of individual cultures and was not age dependent. To further investigate the factors which may be responsible for these differences, the presence of cathepsin D, an aspartic protease responsible for 80% of proteolysis of rhodopsin, was analysed by Western blot. Although the 34 kDa active form of cathepsin D was found in all cultures, in 41% of the cultures higher-molecular-weight forms of cathepsin D were additionally present, thus providing a multimer form of cathepsin D in these cultures. The rate of autofluorescent debris accumulation in cultures possessing a multimer form of cathepsin D was significantly greater (mean 42.3, S.D. +/- 19.8) than those in cultures having a singlet active form (mean 18.8, S.D. +/- 5.5) at 34 kDa (Student's t-test, DF = 15, t = 6.834, P < 0.001). The former cultures included one from a donor with age related macular degeneration, the latter cultures included one from a donor with diabetic retinopathy. This study demonstrates that the rate of autofluorescent debris accumulation in cultured RPE cells is not age dependent, but is an intrinsic property of the donor RPE cells that is possibly related to the presence of a multimer form of the lysosomal enzyme cathepsin D.

Preliminary Evaluation of a Hydrogel Core-and-Skirt Keratoprosthesis in the Rabbit Cornea

BACKGROUND

We developed a core-and-skirt keratoprosthesis, with both components made from poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogels. The identical chemical nature of both spongy skirt and transparent core assures a permanent union between them. We have previously shown that PHEMA sponges, within a certain range of pore size, can support cellular invasion and neovascularization when implanted into the rabbit cornea. The present study is the first to evaluate the behavior of the whole prosthesis after implantation into the rabbit cornea.

METHODS

Hydrogel keratoprostheses were inserted intrastromally into the corneas of seven rabbits and histologically examined by light microscopy in five eyes enucleated at 8, 12, and 14 weeks.

RESULTS

None of the implants extruded over this period. Both clinical and histopathologic examination showed that the keratoprostheses were well tolerated by the host tissue. The porous skirt was fully integrated into the stroma by fibrovascular invasion, and no capsule formed around the implants. Stromal melting anterior to the implant occurred in two cases, but this did not affect the fixation of the keratoprostheses.

CONCLUSIONS

This study indicates that our keratoprosthesis can prevent extrusion in the short term when inserted into an intrastromal pocket of the rabbit eye.

Crosslinked poly(1-vinyl-2-pyrrolidinone) as a vitreous substitute

A hydrogel with a high water content was produced and tested as a possible vitreous substitute. The polymer (poly[1-vinyl-2-pyrrolidinone]) (PVP) was synthesized by free radical bulk polymerization of 1-vinyl-2-pyrrolidinone (VP) in the presence of 0.25% divinyl glycol (DVG) as a crosslinking agent. The fully hydrated polymer, containing about 98% water, was clear, transparent, autoclavable, and easily injected through a small-gauge needle with minimum fragmentation, and without changes in its optical properties. Dynamic mechanical analysis of the hydrogel indicated a covalently crosslinked elastic network both before and after injection. The resilience of hydrogel decreased after being subjected to shear stress during the injection process. A cytotoxicity bioassay of the hydrogel in vitro, using cultured mouse (Balb/ c-3T3) fibroblasts, showed cytostatic but not cytocidal effects. The hydrogel was injected into the vitreous cavity of rabbits and followed up to 4 weeks. The gel was clinically well tolerated, however opacities in the vitreous body were observed following the insertion of the gel. Histopathological examination revealed no adverse reactions to the retina, but the presence of loose polymer particles indicated the possibility of the biodegradation of the polymer. These results suggest the potential use of crosslinked PVP hydrogels as vitreous substitutes, provided that their biodegradation is not significant, a matter that should be further investigated.

Production of neocollagen by cells invading hydrogel sponges implanted in the rabbit cornea

BACKGROUND

Poly(2-hydroxyethyl methacrylate) sponges are artificial tissue-equivalent matrices with potential value as materials for the peripheral zone of artificial corneas. A keratoprosthetic device was developed incorporating a poly(HEMA) spongy skirt which allowed cellular invasion. The present in vivo study investigated the biosynthetic activity of stromal fibroblasts growing within a poly(HEMA) sponge implanted into the rabbit cornea.

METHODS

A porous poly(HEMA) hydrogel was synthesized by polymerization in a large excess of water. Specimens with a pore size larger than 10 microns were impregnated with collagen type I and then implanted into the limbal region of cornea in four rabbits. The animals were followed clinically for 28 days, when they were anaesthetized and new sponge specimens were implanted in their second eye. After 2 h, both eyes were enucleated. The 28-day and 2-h explants were subjected to autoradiographic analysis following labelling with tritiated proline and to an immunostaining technique using antibodies to collagen types I-VI.

RESULTS

The autoradiographic analysis showed that the fibroblasts within the 28-day explants continued to be synthetically active and deposited proteins. Using the immunostaining technique, the deposition was most clearly demonstrated by the localization of collagen type III in the tissue invading the sponge. Both techniques failed to indicate any cellular activity in the short-time implants.

CONCLUSIONS

The presence of collagen type III is consistent with a normal healing response of the stromal fibroblasts and indicates that poly(-HEMA) sponges are able to function as tissue-equivalent matrices.

Poly(1-vinyl-2-pyrrolidinone) hydrogels as vitreous substitutes: histopathological evaluation in the animal eye

A homopolymer of 1-vinyl-2 pyrrolidinone and its copolymer with 2-hydroxyethyl methacrylate, both cross-linked with divinyl glycol, were produced as possible substitutes for the vitreous body of the eye. The hydrated polymers behaved like viscoelastic gels, displaying excellent physical and optical properties. The sterile gels (0.7-1.5 ml) were injected into the vitreous cavity of rabbits, which previously underwent gas-mediated vitrectomy. Clinically, the eyes were quiet, with the exception of transient opacities in the vitreous. After 4 weeks, the operated eyes were enucleated and subjected to histopathological analysis using light and transmission electron microscopy. The common feature in all sections was the invasion of inflammatory cells. Vacuoles containing granular material, assumed to be polymer, were seen in the intercellular spaces of the neural retina, in the retinal pigment epithelium cells, and in macrophages. These findings indicated the fragmentation and phagocytosis of synthetic gels. It appeared that the biodegradation of the internalized polymers did not proceed further, however, the fate of polymers and their usefulness as vitreous substitutes should be investigated through long-term experiments.

Lipofuscin of the retinal pigment epithelium: a review

Accumulation of lipofuscin is one of the most characteristic features of ageing observed in retinal pigment epithelial (RPE) cells. The lipofuscin found in RPE cells differs from that of other body tissues due to the fact that it is mainly derived from the chemically modified residues of incompletely digested photoreceptor outer segments. It is a heterogeneous material composed of a mixture of lipids, proteins, and different fluorescent compounds, the main fluorophore of which has recently been identified as a derivative of vitamin A. Research interest has variously focussed on the roles of age, light damage, free radicals, antioxidants, visual pigments, retinal locus, lysosomal enzymes, and pigmentation on lipofuscin formation, as well as the effects of lipofuscin on RPE cell function and causation of retinal disease. This article reviews the recent advances in knowledge of the composition, origin, and possible deleterious effects of RPE cell lipofuscin.

Visual outcome of excimer laser photorefractive keratectomy for myopia. A comparison of three laser delivery systems in Australia

PURPOSE

To compare the performance of the three excimer laser delivery systems in correcting myopia.

METHODS

The first generation excimer laser systems produced by Summit, VISX and LEI were examined. The first 40 consecutive eyes with six-month refractive results were selected from the LEI centre. Forty consecutive eyes, matched for age and attempted corrections, were then selected from each of the Summit and VISX centres. The postoperative visual results were examined retrospectively and compared among the three groups.

RESULTS

At six-month follow-up, the mean and standard deviation of the spherical equivalent refraction were +0.27 (SD, 0.65) dioptre in the Summit group, -0.33 (SD, 0.83) dioptre in the VISX group and -0.62 (SD, 0.89) dioptre in the LEI group (P = 0.0001, ANOVA). Thirty-five eyes (88%) in the Summit group, 33 eyes (83%) in the VISX group and 28 eyes (70%) in the LEI group achieved corrections within 1 dioptre of intended corrections (P = 0.131, chi 2 test). Four eyes (10%) in the Summit group, two eyes (5%) in the VISX group and one eye (3%) in the LEI group were overcorrected by more than 1 dioptre at six-month follow-up. Unaided visual acuity (Snellen equivalent) was 6/12 or better in 37 eyes (93%) in the Summit group, 34 eyes (85%) in the VISX group and 34 eyes (87%) in the LEI group (data missing in one eye). Loss of one or more lines of best corrected visual acuity (Snellen equivalent) was found in 6 of 39 eyes (15%) in the Summit group, 10 of 40 eyes (25%) in the VISX group and 4 of 36 eyes (11%) in the LEI group (P = 0.258, chi 2 test). Regression between one and six month follow-up differed significantly (P = 0.001, ANOVA) among the groups, with the mean of -1.25 (SD, 0.94) dioptres in the Summit group, -0.59 (SD, 1.01) dioptre in the VISX group and -0.40 (SD, 0.99) dioptre in the LEI group.

CONCLUSIONS

Statistically comparable results were found in the three groups in terms of refraction and visual acuity six months after myopic photorefractive keratectomy. No statistical differences were found between the groups in terms of significant overcorrection or loss of best corrected acuity. The group treated using the Summit system demonstrated significantly greater regression than the other groups, necessitating larger initial hyperopic shifts.

Initial clinical experience with tissue plasminogen activator (tPA) assisted removal of submacular haemorrhage

Tissue plasminogen activator (tPA) (250 micrograms/ml) was used to facilitate removal of submacular thrombus in 15 patients. Following a three-port vitrectomy and subretinal tPA injection (0.1 ml) via a 30 gauge needle, blood was evacuated after enzymatic dissolution for 20 minutes. Two injections were required in some cases. Nine women and six men were treated (mean age 75.5 +/- 8.6 years). Duration of symptoms ranged from 2 days to 8 weeks. One case was due to a retinal macroaneurysm, the others to age-related macular degeneration. Vision improved in 13 patients and remained the same or deteriorated in 2 (mean follow-up 11 +/- 4.9 months). Well-defined subretinal neovascular membranes were identified in 2 patients and occult neovascularisation suspected in 2 others. A cataract developed in 1 case and retinal detachments in 2 others; all were treated successfully. The poor visual prognosis associated with submacular haemorrhage may be obviated by the use of the technique we describe.

Construction of a cDNA library from human retinal pigment epithelial cells challenged with rod outer segments

BACKGROUND

To study genes expressed by retinal pigment epithelial (RPE) cells during phagocytosis and digestion of rod outer segments (ROS), a complementary (c)DNA library was produced using an in-vitro model. The cDNA library can be used to study molecular changes which contribute to the development of diseases due to a failure in outer segment phagocytosis and digestion by RPE cells. Here we demonstrate a way to study genes and their functions using a molecular biological approach and describing the first step involved in this process, the construction of a cDNA library.

METHODS AND RESULTS

Human RPE cells obtained from the eyes of a seven-year-old donor were cultured and challenged with bovine ROS. The culture was harvested and total RNA was extracted. Complementary DNA was transcribed from the messenger (m)RNA and was directionally cloned into the LambdaGEM-4 bacteriophage vector successfully. Some clones were picked and the DNA extracted, to determine the size of the inserts as a measure of the quality of the library.

CONCLUSIONS

Molecular biology and cell culture are important tools to be used in eye research, especially in areas where tissue is limiting and animal models are not available. We now have a ROS challenged RPE cDNA library which will be used to identify genes responsible for degrading phagocytosed debris within the retinal pigment epithelium.

The influence of cerebrospinal fluid pressure on the lamina cribrosa tissue pressure gradient

PURPOSE

To measure the tissue pressure gradient through the optic disk and to determine the relationship between intraocular, cerebrospinal fluid, and retrolaminar tissue pressures. The relationship of optic nerve subarachnoid space pressure to intracranial cerebrospinal fluid pressure also was explored.

METHODS

Micropipettes coupled to a pressure transducer were passed through pars plana and vitreous to enter the optic disk in the anesthetized dog. Using a micromanipulator, pipettes penetrated the optic disk in steps while pressure measurements were taken. In some animals, pipettes also were passed into the optic nerve subarachnoid space. Lateral ventricle cerebrospinal fluid pressure, intraocular pressure, and arterial blood pressure were measured concurrently, and the effect of raising CSF pressure was explored.

RESULTS

Retrolaminar tissue pressure was largely dependent on the surrounding cerebrospinal fluid pressure, which was on average 8.6 +/- 3.5 mm Hg (SD, n = 8) higher, and was independent of intraocular pressure. Most (85% +/- 15% [SD, n = 8]) of the pressure drop between intraocular pressure and retrolaminar pressure occurred across the anterior 400 microns of disk tissue. When the intraocular pressure was 21 mm Hg and the cerebrospinal fluid pressure was zero, retrolaminar tissue pressure averaged 7 mm Hg and the translaminar pressure gradient was 3.08 +/- 0.29 mm Hg/100 microns tissue (SD, n = 3). Optic nerve subarachnoid space pressure was equivalent to lateral ventricular pressure.

CONCLUSIONS

These results show that cerebrospinal fluid pressure largely determines retrolaminar tissue pressure; hence, along with intraocular pressure, it is of major importance in setting the translaminar tissue pressure gradient. Results also demonstrate hydrostatic continuity between the optic nerve subarachnoid space and the lateral ventricle. That the translaminar pressure gradient can vary independently of intraocular pressure may be of importance in understanding the pathophysiology of glaucoma.

Laser-induced chorioretinal venous anastomosis for treatment of nonischemic central retinal vein occlusion

OBJECTIVES

To determine whether a chorioretinal venous anastomosis could be created in humans and to evaluate the influence this has on patients with nonischemic central retinal vein occlusions in whom progressive visual loss developed.

DESIGN

Retrospective study.

PATIENTS

A total of 24 patients with nonischemic central retinal vein occlusions and progressive visual loss.

INTERVENTION

An attempt was made to create a chorioretinal venous anastomosis using laser photocoagulation to enable obstructed venous blood to enter the choroid, thus bypassing the site of occlusion.

MAIN OUTCOME MEASURES

Visual acuity, funduscopic appearance, and rapid sequence fluorescein angiograms.

RESULTS

A successful chorioretinal venous anastomosis was created in eight cases (33%), with improvement in visual acuity and resolution of the funduscopic appearance of venous occlusion in all eight cases. Of the 16 patients (67%) in whom an anastomosis was not successfully created, the ischemic form of central retinal vein occlusion developed in five (31%), and eight (50%) were left with various degrees of macular damage and reduced visual acuity.

CONCLUSIONS

Peripheral chorioretinal venous anastomoses can be created in a nonischemic central retinal vein occlusion and appear to be well tolerated. This technique may have some value in the treatment of patients with this condition; however, to address this fully, a properly constructed randomized prospective clinical trial will need to be performed.

Melanin-containing hydrogel intraocular lenses: a histopathological study in animal eyes

Poly(2-hydroxyethyl methacrylate) hydrogel intraocular lenses, containing adrenochrome-melanin, were manufactured and implanted in animal eyes in order to assess the effect of melanin upon (a) biocompatibility of implants with the eye tissues, and (b) fibrous proliferation of lens epithelium responsible for the opacification of the posterior capsular membrane. An equal number of control lenses were also implanted. The animals were followed up for durations up to two years, and a detailed histopathological examination of the eyes was performed subsequent to their enucleation. The postoperative complications were minor and probably caused by surgical trauma. The study failed to give any indication of the postulated antiproliferative activity of adrenochrome-melanin since minimal capsular opacification occurred in the operated eyes, regardless of the presence of melanin.

Detection and possible functions of a cysteine protease involved in digestion of rod outer segments by retinal pigment epithelial cells

PURPOSE

To investigate the presence and role of a recently cloned cysteine protease (cathepsin S) in the digestion of rod outer segments (ROS) by cultured retinal pigment epithelial (RPE) cells.

METHODS

RPE cell cultures were established from eye bank donor eyes. Total RNA was extracted from freshly harvested cultures, and after reverse transcription, the cDNA was subjected to polymerase chain reaction (PCR). Cathepsin S (Cat S) mRNA translation was inhibited by antisense oligonucleotides, and the effect of inhibition on the accumulation of fluorescent debris was examined. The activity of cysteine and aspartic proteases in ROS-challenged RPE cell cultures was inhibited by leupeptin and pepstatin, respectively. The accumulation of autofluorescent debris within RPE cells was measured by a fluorophotometric flow cytometer. The presence of phagosomes in antisense DNA-inhibited and control cultures was demonstrated by electron microscopy.

RESULTS

The expression of Cat S in RPE cells was demonstrated by RNA-PCR. Using antisense oligonucleotide-mediated-specific inhibition of Cat S, a significant ROS-derived increase in autofluorescence was detected within the RPE cells when they were compared with the unchallenged control cultures and cultures in the presence of ROS and sense oligonucleotides. Electron microscopy demonstrated the presence of a large number of phagosomes that enveloped structures similar to ROS. The accumulation of autofluorescent debris was also demonstrated in cysteine protease-inhibited, ROS-challenged RPE cultures, but it was not detected with aspartic protease inhibition.

CONCLUSIONS

The expression of Cat S in RPE cells and the accumulation of an autofluorescent debris in cultures in which cysteine proteases or Cat S activity is inhibited suggest a key role for this enzyme, either in the ROS digestion process or in the activation of cathepsin D, the major lysosomal enzyme present in RPE cells.

Synthetic polymers as materials for artificial vitreous body: review and recent advances

In spite of a century of recorded attempts to replace the vitreous body of the eye with a foreign material, there is no permanent substitute currently available, and the success of some materials as temporary substitutes is still very limited. Among the large number of materials proposed or tested as vitreous substitutes, synthetic polymers have been episodically considered during the past four decades. This article will review these attempts, their outcomes, and recent progress in this field. There were only seven synthetic polymers and a few semisynthetic polymers (modified biopolymers) so far proposed or tested as vitreous substitutes. It appears that probably a synthetic hydrogel with very high water content would eventually be the material of choice for a permanent vitreous substitute, but the ideal material has not yet been found.

Interpenetrating polymer network (IPN) as a permanent joint between the elements of a new type of artificial cornea

The combination at the interface between two chemically identical polymers was investigated by light and electron (scanning, transmission) microscopy. The polymers constitute elements of a new type of artificial cornea in which the peripheral skirt is made from spongy poly(2-hydroxyethyl methacrylate) (PHEMA) and the central optical zone from homogeneous, transparent PHEMA. Their two-phase combination along the boundary fulfill formally the requirements for an interpenetrating polymer network (IPN). The procedure for the manufacture of prosthesis was described in detail. Thin and ultrathin sections excised from the interface region were investigated using microscopic techniques. Light microscopy allowed the measurement of the diffusion path length of transparent PHEMA into sponge, which was approximately 0.5 mm. Transmission electron microscopy revealed a cellular-like morphology as well as larger segregated zones, which indicated network interpenetration on a molecular level and also a relatively poor miscibility of the two polymers despite their identical chemical structure. The latter was interpreted as a result of the submicroscopic restraints imposed by polymer I (sponge) upon polymer II. This study provides evidence that the interface combination of the prosthetic elements should be regarded as a gradient homo-IPN. This system offers a union between elements much stronger than those previously reported in artificial corneas.

Symptoms and signs of retinal disease

Of all the diseases of the eye, the retinal disorders are perhaps the most frequently misdiagnosed by the general medical community. The content of this article is restricted to retinal diseases and the importance of symptoms and signs in their accurate diagnosis.

193 nm excimer laser sclerostomy in pseudophakic patients with advanced open angle glaucoma

A modified open mask system incorporating an en face air jet to dry the target area during ablation and a conjunctival plication mechanism, which allows ab externo delivery of the 193 nm excimer laser without prior conjunctival dissection, has been developed to form small bore sclerostomies accurately and atraumatically. Full thickness sclerostomies, and sclerostomies guarded by a smaller internal ostium can be created. A pilot therapeutic trial was conducted in pseudophakic patients with advanced open angle glaucoma. Six full thickness sclerostomies (200 microns and 400 microns diameter) and three guarded sclerostomies were created in nine patients by 193 nm excimer laser ablation (fluence per pulse 400 mJ/cm2, pulse rate 16 Hz, air jet pressure intraocular pressure +25 mm Hg). After 6 months' follow up, intraocular pressure was controlled (< or = 16 mm Hg) in eight of the nine patients (6/9 without medication). Early postoperative complications included hyphaema (trace--2.5 mm) (6/9), temporary fibrinous sclerostomy occlusion (4/9), profound early hypotony (all patients without fibrinous occlusion), and suprachoroidal haemorrhage in one case. Conjunctival laser wounds were self sealing. Small bore laser sclerostomy procedures are functionally equivalent to conventional full thickness procedures, producing early postoperative hypotony, with an increased risk of suprachoroidal haemorrhage in association with this. Further research is required to improve control over internal guarding in excimer laser sclerostomy before clinical trials of this technique can safely proceed.

Kinetic studies on phagocytosis and lysosomal digestion of rod outer segments by human retinal pigment epithelial cells in vitro

Using novel methodology, this study describes the kinetics of rod outer segment (ROS) phagocytosis and digestion by human retinal pigment epithelial (RPE) cells in vitro and examines the effect of certain lysosomal enzyme inhibitors on ROS digestion in these cells. Human RPE cells displayed saturation of phagocytosis with respect to both ROS concentration and time. While surface-binding and ingestion phases of ROS phagocytosis saturated after 24-36 h, the rate of ROS digestion reached a maximal level within 24 h. Increasing the concentration of zinc in the culture medium from 1.9 to 100 microM had no significant effect on ROS digestion. The effects of swainsonine (an alpha-mannosidase inhibitor), pepstatin (an aspartic protease inhibitor), and leupeptin (a cysteine protease inhibitor) were also examined. At 6 h, ROS digestion was reduced 27.3 +/- 15.3% by swainsonine, 69.4 +/- 20.9% by pepstatin, and 77.0 +/- 14.4% by leupeptin. The effect of these inhibitors declined with increasing time. This study is the first to demonstrate the functional importance of cysteine and aspartic proteases in the digestion of ROS by RPE cells in vitro.

Automated extraction and quantification of macular drusen from fundal photographs

The objective quantification of drusen (and other macular lesions) should have applications epidemiologically, in the study of the natural history of drusen, and with such instruments as the scanning laser ophthalmoscope. The automated extraction of drusen from photographs is technically difficult because of uneven macular reflectance, and the confusing pattern of darker vessels. We have developed a method using an IBM personal computer, an image digitising board and specially written software. Once the image is digitised, no further input from the operator is necessary. We present the results of manual counting versus automated counting on a small series of patients with drusen. The automated technique is highly reproducible, and will calculate the retinal area occupied by drusen. The area and numbers of drusen can be compared over time, giving an index of progression. Hard drusen are fairly well detected, but the detection of soft drusen with their lower contrast remains a problem. The technique cannot distinguish between drusen and other pale lesions (e.g., atrophic retinal changes).

Significance of Bruch's membrane in the creation of iatrogenic chorioretinal venous anastomosis

Iatrogenic retinal to choroidal vein anastomoses, as a method of bypassing retinal venous occlusions has been reported in dogs in which Bruch's membrane is poorly formed. In order to determine whether chorioretinal venous anastomoses can be induced in an animal with a Bruch's membrane that is well developed as in humans, pigmented rats were chosen. A high intensity, small spot size argon green laser beam of 514 nm was used to induce the anastomosis. Three out of 5 rat eyes developed a retinal vein to choroidal vein anastomosis. The success rate of iatrogenic retinal to choroidal vein anastomoses in the rat was comparable to that obtained in the dog. This study suggests that Bruch's membrane was not significant in the creation of an iatrogenic chorioretinal venous anastomosis.

193-nm excimer laser sclerostomy using a modified open mask delivery system in rhesus monkeys with experimental glaucoma

Excimer laser sclerostomy is a new glaucoma filtration procedure in which the argon fluoride excimer laser at 193 nm is delivered ab externo through a modified open mask system incorporating an en-face air jet to dry the target area and preserve hemostasis during ablation and a conjunctival plication mechanism, which allows the conjunctival and scleral wounds created by through-and-through ablation to separate once the mask is removed. No preparatory dissection of the conjunctiva is required. Five 200-microns and five 500-microns sclerostomies were formed by ablation at a pulse repetition rate of 20 Hz and a fluence per pulse of 400 mJ/cm2 in fellow eyes of five rhesus monkeys with experimental glaucoma. Overall, seven of the ten eyes attained a functional result, with intraocular pressures remaining below 21 mmHg for 6 +/- 1 days and rising to the pre-operative level after 10 +/- 3 days without adjunctive antifibroblast medication. The duration of filtration for 200-microns and 500-microns sclerostomies was similar, and parallels that previously observed for posterior lip sclerectomy in the same animal model. The three eyes with no functional result all had incorrectly positioned sclerostomies. Choroidal detachment and significant shallowing of the anterior chamber did not occur. Excimer laser sclerostomy appears to be a viable technique for filtration, provided that mask placement is accurate.

Pterygium excision with conjunctival autografting: an effective and safe technique

The optimum mode of treatment for symptomatic pterygia would combine efficacy (a low recurrence rate) with safety (freedom from sight threatening complications), and would not affect visual acuity adversely. The efficacy of pterygium excision with conjunctival autografting in a sun exposed population in which pterygia are prevalent has previously been questioned. A cross sectional review of 93 eyes of 85 patients was carried out by slit-lamp examination a minimum of 6 months (range 6-76 months) after pterygium excision and free conjunctival autografting. Case notes were reviewed to obtain details of complications and visual acuity changes related to surgery. Of six recurrences (6.5%) four of these were asymptomatic with minor recurrences. Two patterns of recurrence were identified: cross graft recurrence (three cases) and outflanking (three cases). Complications (wound dehiscence, three cases; Tenon's granuloma one case; conjunctival cyst, one case) were all corrected by minor surgical revision without sequelae. Unaided acuities were unchanged or improved 3 months after surgery in 86 cases, with a minor diminution (1 Snellen line) in seven cases. This study demonstrates a low recurrence rate for a safe technique in an area in which ongoing ultraviolet light exposure levels are high and pterygia are prevalent.

A quantitative study of the lateral spread of Müller cell responses to retinal lesions in the rabbit

A wide variety of retinal pathology is associated with an increase in Müller glial cell expression of glial fibrillary acidic protein (GFAP). In this study the time course and spatial spread of the Müller cell GFAP response following argon laser photocoagulation lesions was examined in wholemounted rabbit retina. At 24 hours single focal lesions were surrounded by GFAP positive Müller cell end feet which declined in density with distance but extended as far as 2-3 mm from the lesion. The Müller cell reaction reached a maximal spread of 4-5 mm at 14 to 21 days and had started to contract by 30 days, leaving a core of GFAP positive processes immediately around the lesion site at 60 days. This zone of spread was much larger than the area of disrupted pigment epithelium. Isodensity plots did not reveal any correlation with the trajectory of retinal ganglion cell axons. The spread of reaction was more confined for lesions within the visual streak than in the dorsal or ventral retinal periphery. Multiple lesions within a focal region of retina resulted in a greater density of GFAP reactive end feet with a corresponding greater spread. However, when five to ten lesions were made in a horizontal row, the Müller cells over the entire retina became GFAP immunoreactive. This pan-retinal reaction took several days to spread, peaked at 7-14 days, and contracted back to the primary lesion sites by 2 months. This spread of Müller cell reactivity may be triggered by the diffusion of substances released by injury or it may be due to direct cellular communication. The extensive indirect effect on Müller cells of laser irradiation might be an important component of the clinical effect of laser photocoagulation and indicates a long distance communication mechanism between retinal glia which is poorly understood. This study also shows the importance of the time at which the Müller cell response is assessed.

Horizontal cells of the normal and dystrophic rat retina: a wholemount study using immunolabelling for the 28-kDa calcium-binding protein

Immunocytochemistry with a monoclonal antibody against the 28-kDa calcium-binding protein (28-kDa CaBP) was used to study horizontal cells in both congenic control (RCS-rdy+) and dystrophic (RCS) 3-month-old rat retina. We found that horizontal cells in the RCS-rdy+ rat retinas were distributed evenly from the centre to the peripheral retina with a mean density of 783 cells mm-2. Cell size ranged between 6.5-12.5 microns in diameter with a mean of 8.87 microns. Individual cell processes could not be followed readily, however they formed a narrow plexus within the outer plexiform layer with the primary dendrites extending radially from each cell soma in an organized manner. In the RCS rat, by contrast, the horizontal cell processes were more disorganized than in the congenic controls. The degree of disorganization varied across the retina. In the posterior pole, where all outer layers had been lost, many processes were grossly swollen along their length and at the tips. The cell somas were also distributed more widely in the depth of the retina. In the peripheral retina, where a debris layer was still present, the processes were less swollen but they extended abnormally widely in depth. Despite the disorganized structure the mean and range of cell size (9.23 microns, 5.5-15.5 microns), and cell density (796 cells mm-2) were similar to that of the control RCS-rdy+ animals. These findings indicate that in dystrophic retinas beyond a certain stage of degeneration the horizontal cells become abnormal in their structure but are present at a normal density and the somas are not grossly swollen or shrunken.(ABSTRACT TRUNCATED AT 250 WORDS)

Severe corneoscleral infection. A complication of beta irradiation scleral necrosis following pterygium excision

OBJECTIVE

To assess the precipitating factors, clinical course, and treatment of 11 cases of severe intraocular infections of radionecrosis after pterygium excision in an attempt to minimize the devastating ocular sequelae.

DESIGN AND SETTING

From the database of cases of radionecrosis at Royal Perth (Australia) Hospital and Lions Eye Institute, Perth, we identified 11 cases of severe intraocular infection complicating radionecrosis. We reviewed the case notes and the available radiotherapy records (n = 8).

PATIENTS

Eleven patients admitted during an 8-year period.

RESULTS

Mean (+/- SD) dose of radiotherapy was 22.7 +/- 1.0 Gy and mean latency period, 14.45 +/- 2.5 years. Among the six proven bacterial cases, Pseudomonas was identified in four, Staphylococcus aureus in one, and Streptococcus pneumoniae was involved in one bilateral case. Among the four fungal cases, Petriellidium boydii was indicated in two, and Fusarium and Scedosporium inflatum in one each. The condition may remain undiagnosed for some time and mimic a posterior scleritis, serous retinal detachment, or pseudotumor.

INTERVENTIONS

Early débridement and culture; close microbiological assistance; and systemic antimicrobials for a prolonged period. Perforation or incipient perforation necessitated penetrating keratoplasties in seven patients and repeated keratoplasties in three.

MAIN OUTCOME MEASURES

The use of radiotherapy following pterygium excision should be limited and only low doses used. Ulcer beds and calcific plaques at sites of radionecrosis should not be directly covered without first performing adequate sterilization. Removal of plaques may precipitate sepsis; ulcer beds and plaques harbor infective agents.

CONCLUSION

Severe radionecrosis may expose a patient to a lifelong risk of intraocular sepsis and profound visual morbidity. Conjunctival autografting is a safer method to reduce recurrence rate after pterygium excision.

Fungal corneoscleritis complicating beta-irradiation-induced scleral necrosis following pterygium excision

Four cases of fungal corneoscleritis complicating beta-irradiation-induced scleral necrosis after pterygium excision have presented to our institution in recent years. Two cases were due to Petriellidium boydii and one each to Fusarium and Scedosporium inflatum. The condition may remain undiagnosed for weeks to months and becomes chronic with perforation or incipient perforation. The infections may masquerade as a chronic red eye, posterior scleritis or serous retinal detachment. Penetrating or lamellar keratoplasty is required following debridement of necrotic tissue. Prolonged systemic antifungal therapy may still fail to eradicate infection. Visual outcome is usually poor, and one of our patients required enucleation. Removal of calcific plaques from ulcer beds should be accompanied by disinfection, debridement and culture, since these beds and plaques are frequently a nidus of infection. Subsequently these ulcers may be covered with lamellar grafts or conjunctiva. We would caution against the use of radiotherapy to prevent recurrence of pterygia.

Tissue interaction with hydrogel sponges implanted in the rabbit cornea

We proposed poly(2-hydroxyethyl methacrylate) (PHEMA) hydrogel sponges as potential materials for the peripheral zone of a composite keratoprosthesis. It was previously shown that such sponges allowed cellular invasion when implanted s.c. in rabbits. To evaluate the reaction elicited by these materials in the corneal tissue, a PHEMA sponge, with pore size diameters of 10-30 microns, was produced, impregnated with collagen, and implanted in the rabbit cornea in both central and limbal regions of separate eyes. The eyes were examined by slit-lamp biomicroscopy up to 6 months postoperatively. Enucleation was performed at 3 weeks, 6 weeks, and 6 months, then excised implants were examined by light and transmission electron microscopy. Both clinical and histopathological examination indicated that sponges were well tolerated by the stromal and limbal tissues. No capsule was formed around any of the implants. Corneal fibroblasts and capillaries readily invaded the internal voids in the sponge to all depths. The invading cells remained viable and active up to the end of the follow-up period. Our findings suggest that hydrophilic PHEMA sponges may be successful as peripheral keratoprosthetic materials able to provide a permanent and tight fusion of the keratoprosthesis with the host tissue.

Transient preservation of photoreceptors on the flanks of argon laser lesions in the RCS rat

In the RCS rat there is a progressive degeneration of the photoreceptors which starts at two to three weeks after birth. We have demonstrated that there is prolonged survival of photoreceptors on the flanks of argon laser lesions made at post-natal day 23, just as degeneration begins. The cells in the outer nuclear layer retained a relatively normal appearance on the flanks of the lesions for the first two weeks and there was a very low percentage of pyknotic cells. By one month some cell loss occurred but much less than in non-irradiated regions where very few cells remained. At two months after lesion there were still elevated numbers on the flanks but only 2-3 rows of cells remained. The prolonged survival correlated with disruption to the pigment epithelial layer, increased migration of phagocytic cells into the outer segment/debris layer and a reduction in thickness of the debris layer at late stages. The mechanisms of this effect are unknown however laser lesions provide a well controlled and reproducible situation in which to study these mechanisms.

Expression of basic fibroblast growth factor and its receptor in the retina of Royal College of Surgeons rats. A comparative study

PURPOSE

The aim of this study was to identify whether abnormalities in the synthesis of basic fibroblast growth factor (bFGF) or its receptor (bFGF-R) were responsible for the photoreceptor dystrophy in Royal College of Surgeons (RCS) rats.

METHODS

The polymerase chain reaction was used to detect the expression of bFGF and bFGF-R messenger RNA in the retinal pigment epithelial (RPE) cells and the neural retina of RCS dystrophic rats and in PVG/C and RCS-rdy+ control animals.

RESULTS

In the RPE, it was found that there was no significant difference in the expression of bFGF and bFGF-R between RCS rats and the controls at the ages of 21 days and 3 mo. In the neural retina, the level of bFGF expression was lower in the 21-day-old RCS rats compared with the control group, but bFGF-R expression was as strong as in the PVG/C and RCS-rdy+ animals. However, in 3-mo-old RCS rat neural retina, the bFGF and bFGF-R expression was found to be significantly lower than in the control animals.

CONCLUSIONS

Although the mutant gene in RCS rats is expressed in the RPE cells, these results suggest that there is no significant defect in bFGF or bFGF-R expression in the RPE cells of RCS rats, which would be an initiating factor in the development of photoreceptor degeneration in these animals. The lowered bFGF levels in the neural retina at early stages (postnatal day 21) may explain the prolongation of photoreceptor survival when exogenous bFGF is injected.

Bilateral streptococcal corneoscleritis complicating beta irradiation induced scleral necrosis

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