Stem cells in the trabecular meshwork: present and future promises

Primary open-angle glaucoma is recognized as a disease of aging, and studies show a relationship between aging and trabecular meshwork (TM) cell density. Human TM cell division occurs primarily in the anterior, non-filtering region. A commonly used glaucoma treatment, laser trabeculoplasty (LTP), triggers and increases cell division, as well as cell migration of these anterior TM cells. These freshly-divided migrating cells repopulate the burned laser sites, suggesting that they are stem cells. Several studies concerning this putative TM stem cell will be discussed.

Short wavelength automated perimetry and tamoxifen use

BACKGROUND/AIMS

Oestrogen receptors (ORs) have been reported to be present in the retina, and the selective oestrogen receptor modulator tamoxifen has been reported to affect colour vision. This study aimed, therefore, to determine whether standard doses of tamoxifen affect visual sensitivities mediated via short wavelength sensitive (SWS) cones.

METHODS

Two types of visual fields were measured for middle aged women who were being treated with 20 mg of tamoxifen daily as adjuvant therapy for early stage breast cancer. Visual fields were measured using short wavelength automated perimetry (SWAP) and frequency doubling perimetry (FDP). For SWAP, 24-2 visual fields were analysed. No subjects had tamoxifen retinopathy or other eye disease. For each type of visual field, mean deviations (MDs) were assessed as a function of the duration of tamoxifen use, using a cross sectional design. In addition, the difference between the two types of MDs was computed after standardisation of each type of MD separately, and this difference itself was evaluated as a function of the duration of tamoxifen use. Duration dependent changes for SWAP were further evaluated as a function of eccentricity within the visual field, and the visual field data were compared with foveal data obtained psychophysically.

RESULTS

SWAP sensitivities depended on the duration of tamoxifen use. Subjects who used tamoxifen for about 2 years or less were significantly more likely than subjects who had longer use to have high MDs. The difference between the standardised SWAP and FDP MDs likewise was significantly related to the duration of use, whereas duration of use effects for FDP itself were reduced or absent. Although the duration of use effect observed for SWAP was strongest in the peripheral portion of the visual field, there was evidence of changes in SWS cone mediated vision even at the fovea.

CONCLUSION

Standard dosages of tamoxifen can affect SWAP visual fields. The effects of tamoxifen are not equivalent for SWAP and FDP, indicating that tamoxifen affects some types of visual pathways preferentially or selectively. SWS cone pathways, in particular, are affected. SWAP appears able to reveal effects of tamoxifen occurring years before completion of the standard 5 year regimen of use.

Refining the primary open-angle glaucoma GLC1C region on chromosome 3 by haplotype analysis

The GLC1C locus for primary open-angle glaucoma (POAG) is inherited as an autosomal dominant trait. This region on chromosome 3 is 11 cM long. DNA samples from members of a Greek and an American GLC1C family were obtained to determine whether additional typing of microsatellite markers in family members might narrow the region. GLC1C family members were evaluated clinically for POAG on the basis of open angles, intraocular pressures, cupping of discs, and visual fields. DNA samples from the Greek and Oregon GLC1C families were used to further refine the GLC1C region using microsatellite markers. A total of 22 affected members were identified in the two families. Common alleles for D3S3637 and D3S3612 were present in the disease haplotype from both families, suggesting that they may have a common founder. A newly diagnosed patient in the American family had a recombination in the distal portion of the GLC1C haplotype. This recombination narrows the GLC1C region from 11 to 4 cM.

In frame fibrillin-1 gene deletion in autosomal dominant Weill-Marchesani syndrome

Weill-Marchesani syndrome (WMS) is a connective tissue disorder characterised by short stature, brachydactyly, joint stiffness, and characteristic eye anomalies including microspherophakia, ectopia of the lenses, severe myopia, and glaucoma. Both autosomal recessive (AR) and autosomal dominant (AD) modes of inheritance have been described and a gene for AR WMS has recently been mapped to chromosome 19p13.3-p13.2. Here, we report on the exclusion of chromosome 19p13.3-p13.2 in a large AD WMS family and show that, despite clinical homogeneity, AD and AR WMS are genetically heterogeneous entities. Because two AD WMS families were consistent with linkage to chromosome 15q21.1, the fibrillin-1 gene was sequenced and a 24 nt in frame deletion within a latent transforming growth factor-beta1 binding protein (LTBP) motif of the fibrillin-1 gene was found in a AD WMS family (exon 41, 5074_5097del). This in frame deletion cosegregated with the disease and was not found in 186 controls. This study strongly suggests that AD WMS and Marfan syndrome are allelic conditions at the fibrillin-1 locus and adds to the remarkable clinical heterogeneity of type I fibrillinopathies.

Ophthalmic drops causing coma in an infant

A 1-month-old infant with Peters anomaly had recurrent episodes of unresponsiveness, hypotension, hypotonia, hypothermia, and bradycardia. An extensive medical evaluation determined these episodes to be caused by brimonidine, an anti-glaucoma agent. There is the potential for serious toxic effects from the systemic absorption of topically applied ophthalmic agents in children.

Flicker sensitivity and cardiovascular function in healthy middle-aged people

OBJECTIVE

To establish normative relations between measures of visual function and cardiovascular variables that are important for age-related disease, including various forms of glaucoma.

METHODS

Foveal flicker sensitivities, resting blood pressures and heart rates, and intraocular pressures were measured in 18 individuals aged 40 to 68 years. All subjects had 20/20 or better visual acuity in the test eye and no evidence of eye disease or glaucoma suspicion on clinical evaluation and medical history. No subjects were using medication to lower blood pressure. Flicker sensitivity was measured by increasing the illuminance of a fully modulated 20-Hz test stimulus until flicker was perceived. Two test-background stimulus combinations were used: a 570-nm ("yellow") test on a predominantly long-wavelength ("magenta") background and a 580-nm ("yellow") test on a 580-nm ("yellow") background. The illuminance of the yellow background was dimmer than that typically used for short-wavelength automated perimetry, whereas the illuminance of the magenta background was greater.

RESULTS

The 2 flicker sensitivity measures were distinguished by the strong dependence of the magenta background measure on the ratio of mean arterial blood pressure to heart rate. Log flicker sensitivity on this background generally could be modeled as a linear combination of age, intraocular pressure, and ratio of mean arterial blood pressure to heart rate. The optimal model accounted for 84% of the variance (R = 0.92) from all but 2 outlying individuals. After age and intraocular pressure effects were partialed out, an increasing ratio of mean arterial blood pressure to heart rate was strongly associated with decreasing flicker sensitivity.

CONCLUSIONS

Reduced cardiovascular function impacts the ability of the normal visual system to adapt and regulate flicker sensitivity. Elevated intraocular pressure and increased age reduce flicker sensitivity relatively uniformly across a range of stimulus conditions. Because the ratio of mean arterial blood pressure to heart rate equals total peripheral vascular resistance multiplied by cardiac stroke volume, and because total peripheral resistance is determined largely at the arterioles, it is likely that even modest changes in arteriolar function are associated with measurable alterations of visual function. Arch Ophthalmol. 2000;118:1049-1055

Mediation of laser trabeculoplasty-induced matrix metalloproteinase expression by IL-1beta and TNFalpha

PURPOSE

Laser trabeculoplasty of the anterior uveal region of the trabecular meshwork induces sustained matrix metafloproteinase expression within the juxtacanalicular region of the meshwork. Studies were conducted to test the hypothesis that a factor mediates this response and to identify the factor.

METHODS

Human anterior segment organ cultures were subjected to laser treatment using standard clinical parameters and were returned to culture for 8 hours. The resultant 8-hour-conditioned culture medium was then tested for factor activity by evaluating its ability to produce two typical trabecular responses to laser treatment, that is, to induce stromelysin expression or to trigger cell division, when applied to fresh organ cultures or to cell cultures. Confocal immunohistochemistry of the laser-treated organ cultures and western immunoblot analysis of the conditioned medium were used to evaluate changes in potential candidates for the factor activity. The ability of the interleukin (IL)-1 receptor antagonist (IL-1ra)- and of tumor necrosis factor alpha (TNFalpha)- blocking antibodies to eliminate the stromelysin induction was evaluated.

RESULTS

Medium conditioned for 8 hours induced typical trabecular cell division in anterior segment organ cultures. Medium conditioned for 8 hours, but not for 30 minutes, induced typical increases in stromelysin expression in these organ cultures and in cell cultures. After 8 hours, both trabecular cells in laser-treated organ cultures and in the conditioned medium contained elevated levels of IL-1beta and TNFalpha. The laser-treated organ cultures contained elevated levels of IL-1alpha, but it was not secreted into the medium. The ability of conditioned media to induce stromelysin expression was partially blocked by either the IL-1ra- or the TNFalpha-blocking antibody.

CONCLUSIONS

Laser trabeculoplasty induces the expression and secretion of both IL-1beta and TNFalpha within the first 8 hours after treatment. These cytokines then mediate increased trabecular stromelysin expression. Putatively, this initiates remodeling of the juxtacanalicular extracellular matrix, a likely site for the aqueous outflow resistance, and thus restores normal outflow facility.

GLC1F, a new primary open-angle glaucoma locus, maps to 7q35-q36

BACKGROUND

A large family with adult-onset primary open-angle glaucoma (POAG) was identified.

OBJECTIVE

To initiate a genome-wide scan to map the POAG locus in this family.

METHODS

Blood samples or buccal swabs were obtained from 25 members of a large family with POAG after informed consent was obtained. Members and their spouses were evaluated clinically for POAG on the basis of intraocular pressures, cupping of discs, and visual fields. DNA samples were used for a genome-wide screen using microsatellite markers.

RESULTS

Ten affected family members in 4 generations showed evidence of POAG including intraocular pressures of 22 mm Hg or more, and/or optic cup-disc ratios of 0.6 or more, and/or visual field defects consistent with glaucomatous damage. Primary open-angle glaucoma segregated as an autosomal dominant trait, with the disease locus mapping to 7q35-q36 between markers D7S2442 and D7S483 with a multipoint lod score of 4.06.

CONCLUSION

A sixth gene for POAG (GLC1F) has been mapped to 7q35-q36 in a family with at least 4 generations affected.

CLINICAL RELEVANCE

The mapping of this locus further confirms that primary open-angle glaucoma is a heterogeneous group of diseases with at least 6 different loci resulting in a similar phenotype. The eventual ability to classify which major POAG gene an affected person carries could have ramifications for selecting the most effective treatment regimen for that person.

Effect of matrix metalloproteinases activity on outflow in perfused human organ culture

PURPOSE

To test the hypothesis that extracellular matrix turnover, mediated by the matrix metalloproteinases, modulates aqueous humor outflow facility in a human outflow model.

METHODS

Matrix metalloproteinase activity was manipulated and outflow facility evaluated using perfused human anterior segment organ culture. Purified matrix metalloproteinases, tissue inhibitors of metalloproteinases (TIMPs), and several families of synthetic inhibitors of matrix metalloproteinases were added to the perfusion medium. Matrix metalloproteinase expression was increased by adding recombinant interleukin (IL)-1alpha. Kinetic inhibition analysis was conducted for stromelysin, gelatinase A, and gelatinase B with the various inhibitors. Live-dead staining was used to evaluate culture viability.

RESULTS

Increasing metalloproteinase activity, by adding purified metalloproteinases or by inducing their expression by IL-1alpha treatment, increased outflow facility. Inhibition of endogenous trabecular metalloproteinase activity using TIMP or several families of synthetic metalloproteinase inhibitors reduced outflow rates. The elevation and the reduction of outflow rates were reversible, with changes requiring 1 to 3 days. Kinetic enzyme inhibition analysis produced 50% inhibitory concentration values for these inhibitors that were compatible with the concentration ranges for outflow inhibition. CONCLUSIONS. The ability of several specific matrix metalloproteinase inhibitors to reduce outflow facility implies that endogenous extracellular matrix turnover by these enzymes was required for the maintenance of trabecular outflow resistance, at least in this human culture model. These observations provide support for the hypothesis that controlled extracellular matrix turnover is important in the regulation of aqueous humor outflow facility.

Prospects for genetic intervention in primary open-angle glaucoma

Recent advances in glaucoma genetics hold potential for dramatically changing the clinical care of glaucoma patients. To date, 5 primary open-angle glaucoma genes and 2 congenital glaucoma genes have been mapped. As more glaucoma genes are identified, earlier diagnosis for glaucoma should become more readily available. Progress in molecular genetics holds considerable promise for both current and future therapy of glaucoma. Glaucoma classification will be tailored to each individual based upon that person's family history, i.e. family glaucoma genotype. In the future, the optimum treatment for a specific glaucoma patient might rely on the knowledge of the phenotype of that person's causal gene, without having to resort to 'trial and error'. At this time, glaucoma treatment is restricted to lowering intraocular pressure. In the near future, with the knowledge of the pathophysiology caused by the defective glaucoma gene, more traditional drug treatments may be used to bypass the gene defect. Ultimately, gene therapy would replace the mutant gene with a normal one before visual loss has occurred as has been done with a model for retinitis pigmentosa, the retinal degeneration mouse.

Growth factor and cytokine modulation of trabecular meshwork matrix metalloproteinase and TIMP expression

PURPOSE

We hypothesize that regulated trabecular extracellular matrix (ECM) turnover, initiated by the matrix metalloproteinases, is critical for the maintenance of normal aqueous humor outflow rates. However, very little is known about the regulation of trabecular ECM turnover. To identify candidate trabecular regulators, we evaluated the effects of several growth factors and cytokines on trabecular matrix metalloproteinase and TIMP expression.

METHODS

Porcine trabecular meshwork cells were treated with several doses of a variety of growth factors and cytokines and culture media was analyzed after 24, 48, and 72 h. Zymograms were used to evaluate stromelysin, gelatinase A and B activity levels, while immunoblots of Western transfers were used to evaluate stromelysin, collagenase, TIMP-1 and TIMP-2 protein levels.

RESULTS

A phorbol mitogen (TPA), and TNF alpha and beta, interleukin-1 alpha and PDGF BB stimulate gelatinase B, stromelysin, interstitial collagenase and TIMP-1 expression, while having negligible effects on gelatinase A expression; TIMP-2 levels are reduced by TNF but not affected by the other treatments. Acidic and basic FGF, IL-1 beta, TGF beta and PDGF AB produce similar but smaller effects, while HGF, VEGF, EGF, KGF, and LIF produce small to moderate elevations in stromelysin with minimal other responses. PDGF AA, gamma INF, oncostatin-M and endothelin-1 produce negligible changes in these proteinases and inhibitors.

CONCLUSIONS

In addition to providing potential ways to modulate trabecular metalloproteinase and TIMP levels, the responsiveness of these cells to some of these growth factors and cytokines suggests possible roles in normal or pathogenic trabecular cell regulation and some may affect aqueous humor outflow.

Proteoglycan expression by human trabecular meshworks

PURPOSE

Proteoglycans may serve important roles in trabecular meshwork structure or function. Detailed molecular characterization and identification of specific trabecular proteoglycan core proteins has been limited.

METHODS

Radiolabeled proteoglycans were extracted from cultured human trabecular meshworks and subjected to ion exchange and molecular sieve chromatography. Peaks were subjected to glycosaminoglycan content analysis. Reverse transcription with polymerase chain reaction was used to identify trabecular mRNAs of several common proteoglycan core proteins. Western immunoblots of trabecular extracts were also utilized to identify these proteoglycan core proteins.

RESULTS

The proteoglycans elute from ion exchange columns at high salt and molecular sieve column profiles, and they exhibit broad peaks typical of the proteoglycan microheterogeneity seen in other tissues. The four common glycosaminoglycan side-chains were identified on these proteoglycans. Trabecular cells in organ or cell culture contain mRNAs coding for decorin, biglycan, versican, perlecan and a basement membrane glycoprotein, SPARC. Syndecan-1 transcripts were present at very low levels, while aggrecan transcripts were not detectable. Decorin, biglycan, versican and perlecan core proteins were also identified by immunoblots of trabecular cell extracts.

CONCLUSIONS

Several common proteoglycans are expressed by trabecular cells in organ explant or cell culture. Their general characteristics are not unlike those found in other tissues. These proteoglycans may serve important functions in the trabecular outflow pathway.

Mapping a gene for adult-onset primary open-angle glaucoma to chromosome 3q

Glaucoma is the third-leading cause of blindness in the world, affecting >13.5 million people. Adult-onset primary open-angle glaucoma (POAG) is the most common form of glaucoma in the United States. We present a family in which adult-onset POAG is inherited as an autosomal dominant trait. Twelve affected family members were identified from 44 at-risk individuals. The disease-causing gene was mapped to chromosome 3q21-24, with analysis of recombinant haplotypes suggesting a total inclusion region of 11.1 cM between markers D3S3637 and D3S1744. This is the first report of mapping of an adult-onset POAG gene to chromosome 3q, gene symbol GLC1C.

Weill-Marchesani syndrome--possible linkage of the autosomal dominant form to 15q21.1

Weill-Marchesani syndrome comprises short stature, brachydactyly, microspherophakia, glaucoma, and ectopia lentis is regarded as an autosomal recessive trait (McKusick 277600). We present two families each with affected individuals in 3 generations demonstrating autosomal dominant inheritance of Weill-Marchesani syndrome. Linkage analysis in these 2 families suggests a gene for Weill-Marchesani syndrome maps to 15q21.1. The dislocated lenses and connective tissue disorder in these families suggests that fibrillin-1 and microfibril-associated protein 1, which both map to 15q21.1, are candidate genes for Weill-Marchesani syndrome. Immunohistochemistry staining of skin sections from family 1 showed an apparent decrease in fibrillin staining compared to control individuals.

Laser trabeculoplasty induces stromelysin expression by trabecular juxtacanalicular cells

PURPOSE

The mechanism by which laser trabeculoplasty reduces elevated intraocular pressure in primary open-angle glaucoma has been established. To test the hypothesis that trabecular extracellular matrix turnover is involved, stromelysin expression after laser treatment of anterior segment organ cultures was evaluated.

METHODS

Argon laser trabeculoplasty, using typical clinical treatment parameters, was applied to anterior segment organ cultures. Stromelysin levels and activity were then evaluated at various times by immunoblots of Western transfers and by zymography. Stromelysin mRNA levels were evaluated by dot blot and by reverse transcription, followed by polymerase chain reaction amplification. Stromelysin protein was localized by immunohistochemistry, and image analysis was used for quantitation. Stromelysin mRNA was localized by in situ hybridization.

RESULTS

Trabecular stromelysin protein, activity, and mRNA levels were detectably elevated by 8 hours and were several-fold higher by 24 hours after treatment. Stromelysin immunostaining was elevated dramatically in the juxtacanalicular and insert regions of the meshwork, but only modestly in other regions. Stromelysin mRNA increases also were localized primarily to these regions. The juxtacanalicular stromelysin immunostaining increase was sustained for at least 1 week, whereas the insert levels declined somewhat after day 2.

CONCLUSIONS

A stromelysin increase, localized primarily to the juxtacanalicular region of the meshwork, the putative site of the aqueous humor outflow resistance, should degrade trabecular proteoglycans, the putative outflow resistance source, and allow their uptake and further degradation by the juxtacanalicular cells. If diminished juxtacanalicular extracellular matrix turnover is responsible for the glaucomatous reduction in aqueous humor outflow, an increase in stromelysin in this specific area of the meshwork should ameliorate the problem. Thus, the observations support the working hypothesis and may explain the efficacy of this treatment for glaucoma.

Foveal adaptation abnormalities in early glaucoma

Foveal sensitivities were measured after onset of adapting background fields for each of the following four groups of subjects aged 40-70 years: (1) low-tension glaucoma subjects with minimal field loss in the test eye, (2) primary open-angle glaucoma subjects with minimal field loss in the test eye, (3) normal control subjects, and (4) subjects originally enrolled as control subjects but subsequently found, on the basis of masked clinical evaluation, to be suspect for glaucoma despite ostensibly normal intraocular pressures. We found that the desensitization of a short-wavelength-sensitive-cone-mediated response after onset of a 580-nm background field was diminished from that of normal observers for low-tension glaucoma subjects but not for primary open-angle glaucoma subjects. The desensitization was also diminished for a glaucoma-suspect subjects aged 60-70 years. In contrast, the flicker sensitivity instabilities that persisted after onset of a long-wavelength background field for the majority of subjects with primary open-angle glaucoma [J. Glaucoma Suppl. 3, S19 (1994)] occurred only infrequently among the other subject groups. These results imply that glaucoma often involves the fovea, probably by affecting retinal subtractive adaptation processes, although with different consequences for different types of glaucoma. The results also suggest that undiagnosed low-tension glaucoma may not be rare in the general aging population.

Early changes in matrix metalloproteinases and inhibitors after in vitro laser treatment to the trabecular meshwork

Extracellular matrix turnover in the trabecular meshwork may play a role in regulating aqueous humor outflow. Laser trabeculoplasty is a common treatment for open-angle glaucoma. The mechanism of this treatment is not understood. We investigated changes in the levels and expression of the matrix metalloproteinases and their tissue inhibitors (TIMPs) in this tissue using cultured human anterior segment explants and standard clinical-parameter laser treatment. Medium gelatinase A activity levels are relatively high for sham-treated controls and are not changed dramatically following laser treatment. Medium gelatinase B and stromelysin activity levels are low in sham-treated explants and increase significantly by 24 h after treatment. TIMP1 levels, as assessed by immunoblots of Western transfers, are initially low. However, by 24 h TIMP1 levels have increased significantly. Using semi-quantitative reverse transcription and the polymerase chain reaction, mRNA levels of stromelysin, gelatinase B and TIMP1 are shown to increase after laser treatment, while gelatinase A and TIMP2 remain relatively constant. The increases in trabecular stromelysin and gelatinase B in response to laser trabeculoplasty may have important implications for the mechanism of action of this treatment for open-angle glaucoma.

The effect of melatonin on aqueous humor flow in humans during the day

BACKGROUND

Aqueous humor flow through the anterior chamber of the eye undergoes a circadian cycle. The rate of flow during the day is twice as high as the rate of flow at night. The pineal hormone, melatonin, also undergoes a circadian cycle. Melatonin levels are high at night, whereas aqueous humor flow is low. The authors studied the effect of oral melatonin on aqueous humor flow in humans.

METHODS

The effect of melatonin on aqueous humor flow was evaluated in 19 healthy human volunteers in a randomized, masked crossover study with a placebo control. The hormone or placebo was administered orally during the day when endogenous levels of melatonin are low. Aqueous flow was measured by fluorophotometry for 8 hours.

RESULTS

The mean rate of flow during melatonin treatment was 2.71 +/- 0.64 microliters/minute (+/- standard deviation). The rate of flow during placebo treatment was 2.80 +/- 0.66 microliters/minute. There is no statistically significant difference between these two rates (P = 0.4). With a sample size of 19, the study has a power of 92% to detect at least a 15% difference in the rate of flow under the two conditions. Measurement of plasma concentration of melatonin in five subjects confirmed that concentrations after oral dosage reached peaks comparable with the normal endogenous nocturnal peaks.

CONCLUSIONS

The authors conclude that melatonin concentrations during the day, comparable with plasma concentrations that occur spontaneously during sleep, do not suppress aqueous humor formation. The authors find no support for the idea that plasma melatonin, per se, can suppress aqueous formation or that the circadian rhythm of plasma melatonin is primarily responsible for the circadian rhythm of aqueous humor flow.

Foveal flicker sensitivity abnormalities in early glaucoma: associations with high blood pressure

This study tested the hypothesis that (a) evidence of foveal visual dysfunction could be elicited in glaucoma subjects by measuring flicker sensitivity as a function of time after onset of an adapting field for a suitably chosen set of test and adaptation parameters and that (b) such dysfunction would be related to high blood pressure. Three groups of subjects were tested: (a) subjects with primary open-angle glaucoma but only minimal field loss, (b) normal control subjects, and (c) control subjects found to be suspect for glaucoma. The protocol included measurement of pulse rate and blood pressure, administration of Humphrey 30-2 visual fields and optic nerve head photography, and administration of a battery of psychophysical tests in Maxwellian view. This battery included a test of flicker sensitivity measured at middle wavelengths as a dynamic function of time after onset of a long-wavelength adapting field. The dynamic light-adaptation functions of subjects with glaucoma were much more likely to be unstable than were the corresponding functions of normal subjects. In addition, the dynamic light-adaptation functions of subjects with high blood pressure for their pulse rate were significantly less stable than the correspond ing functions of subjects without high blood pressure for their pulse rate. Moreover, the ratio of mean arterial pressure to pulse rate was significantly less for normal subjects than for either glaucoma subjects or for glaucoma-suspect subjects. We infer that among people with primary open-angle glau coma but with only minimal field loss, there often is foveal dysfunction associated with cardiovascular disease. Evidence of such dysfunction appears to require the use of stimulus conditions that tax the ability of the visual system to respond appropriately.

DNA replication in the cat trabecular meshwork after laser trabeculoplasty in vivo

The in vivo response to laser trabeculoplasty (LTP) was evaluated by measuring the incorporation of thymidine into DNA in the nuclei of trabecular meshwork cells. incorporation into DNA was analyzed by light microscopic autoradiography and by scintillation counting of trabecular extracts. Sixteen cats received argon LTP at a power setting of either 0.3 or 1.0 watt with the contralateral eye serving as a control; a 48-h exposure to HT began 1, 5, or 12 days later. The level of HT incorporation into DNA for LTP-treated eyes was significantly higher than controls for the earliest labeling period, but not at the later time points. This pattern was observed for both 0.3-and 1.0-watt treatments. In a second experiment, LTP was performed on six animals; a power setting of 0.3 watt was used in the left eye, and a power setting of 1 watt was used in the right eye. All 12 eyes were radiolabeled for 48 h with HT beginning 1 day after LTP. A small but significant difference in incorporation levels was found between these two power settings. Trabecular cell division may play a role in the therapeutic efficacy of LTP in glaucoma patients.

Regulation of the levels of human trabecular matrix metalloproteinases and inhibitor by interleukin-1 and dexamethasone

PURPOSE

The regulation of the trabecular meshwork's extracellular matrix is poorly understood and may involve a family of secreted proteinases, the matrix metalloproteinases. Because the trabecular extracellular matrix has been hypothesized to affect intraocular pressure, an evaluation was made of the ability of two cellular modulators to change the levels of matrix metalloproteinases in the medium of human trabecular meshwork organ explant cultures.

METHODS

Trabecular explant cultures were exposed to recombinant human interleukin-1 alpha, dexamethasone, or combinations thereof for 72 hours and the culture medium was collected for analysis. Levels of stromelysin, the 72 kD gelatinase A and the 92 kD gelatinase B enzyme activity in this culture medium were assayed by substrate gel electrophoresis (zymography). Stromelysin and the tissue inhibitor of metalloproteinases (TIMP1) media protein levels were analyzed using immunoblots of Western transfers.

RESULTS

Culture medium of unstimulated explants contains significant levels of the 72 kD gelatinase A and only low levels of the 92 kD gelatinase B, stromelysin, and TIMP1. Interleukin-1 alpha produces a dose-dependent several-fold elevation of gelatinase B, stromelysin, and TIMP1 without changing gelatinase A levels. Dexamethasone produces no significant change in gelatinase A and only small increases in stromelysin, gelatinase B, and TIMP1. When added together, dexamethasone antagonizes the interleukin-1 alpha-induced increase of stromelysin, gelatinase B, and TIMP1 in a dose-dependent manner.

CONCLUSION

These modulators may be useful in analyzing the roles of this enzyme family in normal trabecular homeostasis and perhaps in the etiology of glaucoma.

Ocular inflammatory effects of intravitreally injected interleukin-2

The primary, known physiologic effect of interleukin-2 (IL-2) is to act as a T lymphocyte growth factor. We investigated the potential contribution of IL-2 to intraocular inflammation by studying the inflammation resulting from the intravitreal injection of recombinant, human IL-2 in New Zealand white rabbits. Serial slit lamp observations indicated that 40 microgram of intravitreally injected IL-2 induced an anterior uveitis which was maximal 5 days after the injection. Inflammation was less marked but still significant with amounts of IL-2 as low as 400 ng. Direct examination of aqueous humor confirmed elevations of protein, prostaglandin E2, and mononuclear cells which correlated with the clinical observations. The kinetics of the response to intravitreal IL-2 distinguished it from the responses to other intravitreally injected cytokines such as interleukins 1, 6, or 8 as well as tumor necrosis factor. Intramuscular injection of cyclosporine A significantly reduced the protein extravasation associated with IL-2 injection, but cyclosporine had no effect on inflammation secondary to an intravitreal injection of interleukin-1. These observations implicate IL-2 as a potential contributor to uveitis. In addition, the studies with cyclosporine indicate the heterogeneity of inflammation such that pharmacologic agents which affect one cause of uveitis are not necessarily efficacious in another model.

A clinicopathologic correlative study of noncontact transscleral Nd:YAG cyclophotocoagulation

We studied the histopathologic changes of three eyes enucleated two weeks, eight weeks, and 17 months, respectively, after noncontact Nd:YAG cyclophotocoagulation. The histologic findings at two weeks were destruction of the nonpigmented and pigmented ciliary body epithelium, occlusion of the capillaries of the ciliary processes, and ciliary body stromal necrosis in the region of the processes. Hyperplasia of the pigmented and nonpigmented epithelium, fibrosis and near total atrophy of the ciliary processes, and partial atrophy of the ciliary muscles were present at eight weeks and 17 months. We concluded that application of treatment 1.0 to 1.5 mm posterior to the corneoscleral limbus selectively destroys the pars plicata, and that, histologically, the mechanism for reducing intraocular pressure appears to be destruction of ciliary processes with reduction of aqueous formation.

Profound reductions of flicker sensitivity in the elderly: can glaucoma involve the retina distal to ganglion cells?

Flicker sensitivities were measured for more than 100 people age 60 and older with stimulus-conditions originally designed to obtain estimates of preretinal absorption by the lens and macular pigment. Flicker sensitivities were measured on two chromatic backgrounds: a 1000-td, 480-nm background and a 5800-td, Wratten 33 background (approximately metameric with 633 nm). Testing sessions were administered at 18-month intervals across a 3-yr period. No subject tested had a history of glaucoma or ocular hypertension at the time of entry into the study. For ten subjects, however, flicker sensitivity was sometimes reduced by more than 2.0 log units from the mean norm for at least one of the two backgrounds. For most other subjects, flicker sensitivities were within 0.5 log units of the mean norms. On retrospective analysis, the profound reductions of flicker sensitivity (PRFS) were associated significantly with (a) advanced age (perhaps especially when combined with relatively high intraocular pressure), and (b) the use of cardiovascular medications. The PRFS probably were associated with (c) female sex, and (d) large intraocular pressure fluctuations. In addition, the majority of subjects with PRFS were found to have evidence of glaucomatous cupping or field loss. These results suggest that PRFS result from glaucoma or share etiologies with low-tension glaucoma. The use of cardiovascular medications suggested that PRFS could depend on retinal dysfunction rather than on optic nerve compromise alone. Predicted results from two additional subject populations support this possibility. For young healthy subjects, flicker threshold vs illuminance curves attained very steep slopes for sufficiently short wavelength tests on sufficiently extreme long wavelength backgrounds (655 nm, 50,000 td); the steep slopes coincided with the breakdown of effective M-cone isolation. Reductions of flicker sensitivity on the 5800-td Wratten 33 background depended correspondingly on test wavelength for subjects with well-documented low-tension glaucoma.

Synthesis of platelet activating factor by ocular tissue from inflamed eyes

Platelet activating factors (PAFs) are a family of ether lipids with properties that suggest a major role in inflammation. We have previously implicated PAFs in ocular inflammation based on the inhibition of several rabbit models of iritis with a specific PAF receptor antagonist. We have tested ocular tissues for the ability to synthesize PAF. Iris, ciliary body, cornea, and/or retina were carefully dissected from New Zealand white rabbits, and tissue from four eyes was pooled. Tissues were stimulated with calcium ionophore (10 mumol/L), and supernatants were extracted with chloroform-methanol. Platelet-aggregating activity was found in the chloroform phase in 2 of 9, 1 of 8, 0 of 9, and 3 of 9 studies involving iris, retina, ciliary body, or cornea, respectively. Twenty-four hours after the intravitreal injection of 125 ng of endotoxin, aggregating activity was consistently detectable from supernatants of stimulated iris and ciliary body, occasionally present from stimulated retina but not detectable from cornea. The shape of the aggregation curve resembled that produced by 0.5 to 2.0 ng of authentic PAF. Moreover, the aggregation could be completely inhibited by a PAF receptor antagonist and the aggregating activity chromatographed identically on high-performance liquid chromatography to a PAF standard. These studies indicate that PAF-like activity could be detected from several ocular tissues subsequent to inflammation. Iris, ciliary body, retina, vascular endothelium, and/or leukocytes could each contribute to the presence of this inflammatory mediator.

Propagation of human corneal endothelium in vitro effect of growth factors

Endothelial cells were obtained from 23 human corneal-scleral rims. Donors were 0.2-37 yr of age. Most cultures obtained from donors under 30 yr ceased to grow after the seventh passage (3-24 weeks). Growth from 17- and 25-yr-old donors were maintained for nine passages (26 weeks) and 18 passages (100 weeks), respectively. Cultures were established from 12 rims, using growth factors in uncoated culture flasks or epidermal growth factor (EGF) in an extracellular matrix-coated (ECM) flask. EGF improved the growth potential of the cells; a combination of an ECM-coated-tissue culture flask with EGF in the medium provided an improved environment for continuous growth.

Expression of matrix metalloproteinases and inhibitor by human trabecular meshwork

Extracellular matrix (ECM) turnover and remodeling are initiated, at least in part, by the regulated secretion of members of a family of matrix metalloproteinases. Human and bovine trabecular mesh-work in culture secrete interstitial collagenase, both the 72- and the 92-kD forms of type IV collagenase (gelatinases) and stromelysin, and the tissue inhibitor of metalloproteinases (TIMP). These proteinases and TIMP were identified by immunoblotting western transfers from sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) using several specific antiprotein and antipeptide polyclonal antibodies. Gelatinase and stromelysin enzymatic activities were also analyzed by substrate SDS-PAGE, in which proteinase substrates were polymerized into the gels before electrophoresis to allow subsequent activity assays. These matrix metalloproteinases and TIMP are secreted at low basal levels into trabecular culture medium; their secretion levels are increased several-fold by treatment of the cultures with the phorbol mitogen. 12-O-tetradecanoylphorbol-13-acetate (TPA). Characteristics of the trabecular matrix metalloproteinases and TIMP are similar to those secreted by numerous other tissues, including the retinal pigment epithelium. These proteinases may serve an important role in the maintenance and regulation of the trabecular extracellular matrix and, subsequently, of the aqueous humor outflow pathway in normal and glaucomatous eyes.

Use of gas permeable contact lenses following trabeculectomy

Some patients require a contact lens after glaucoma filtering surgery. The visual rehabilitation of such eyes can be challenging. We report on a total of eight eyes (seven patients) fit with lenticular-design, rigid gas permeable (RGP) contact lenses after the successful establishment of a filtering bleb. In follow-up (mean: 40 months), all patients have successfully worn lenses without adverse effects. We believe that, with careful fitting, close monitoring, and appropriate patient selection, the presence of a filtering bleb need not be a contraindication to contact lens wear, particularly when a smooth-edged, rigid gas permeable (RGP) daily wear lens is used.

Dolichoectasia and cranial nerve palsies. A case report

An elderly man with glaucoma and acute onset of left-sided cranial nerve III, V, and VII palsies was found to have associated marked intracranial artery dolichoectasia. Dolichoectasia (arterial elongation and distension) affects the intracranial arteries, producing various neurological and ophthalmological findings. The patients are usually men who are more than 40 years old and have a history of hypertension. Diagnosis is made by characteristic radiologic findings. In patients with neurologic symptoms and signs suggesting a space-occupying mass, intracranial dolichoectasia should be considered.

The effect of epinephrine and benzalkonium chloride on cultured corneal endothelial and trabecular meshwork cells

We evaluated the effect of dipivefrin hydrochloride, epinephrine hydrochloride, epinephrine borate and their respective vehicles with and without the preservative benzalkonium chloride, on the in vitro growth characteristics of human corneal keratocytes, endothelial cells and trabecular meshwork. Epinephrine hydrochloride and borate at low concentrations (0.0002%) significantly inhibited growth of both trabecular meshwork and corneal endothelial cells. Higher concentrations (0.02%) of these same drugs induced the same effect on the growth of keratocytes in vitro. Similar observations were made on the effect of dipivefrin hydrochloride on human corneal cells in vitro. Benzalkonium chloride alone was demonstrated to be responsible for the growth inhibitory effects on trabecular cells. The susceptibility of trabecular meshwork cells in culture to the commonly used ophthalmic preservative benzalkonium chloride is demonstrated.

Trabecular repopulation by anterior trabecular meshwork cells after laser trabeculoplasty

To study further the transient increase in trabecular cell division within the first two days after laser trabeculoplasty in human corneoscleral explant organ cultures, we used a pulse-chase protocol in which immediately after laser treatment 3H-thymidine was added to the culture medium for 48 hours (the pulse period). Fresh medium without radiolabel was then added for variable times (the chase period) before termination of the experiment. Autoradiography was used to follow changes in the regional distribution of the cells that divided during the pulse period and had 3H-thymidine-labeled DNA. Laser-treated explants, evaluated after a pulse with no chase, showed a fourfold increase in cell division (P less than .001) over nontreated controls. Nearly 60% of this cell division was localized to the anterior, nonfiltering region of the trabecular meshwork where it inserts into the cornea beneath Schwalbe's line. Trabecular cell division in other regions of the meshwork was not increased over controls at this time. After seven or 14 days of chase without radiolabel, the regional distribution of radiolabeled cells changed in laser-treated explants but not in controls. By 14 days, only 26% of the labeled cells remained in this anterior insert region, while 60% were found in the region of the burn sites. Macroautoradiography of whole explants corroborated these observations. Our data support the hypothesis that laser trabeculoplasty causes early cell division by a population of cells in the anterior meshwork; these new cells then migrate and repopulate the burn sites over the next few weeks.

The effect of repeat argon laser trabeculoplasty

A select population of patients received repeat laser trabeculoplasties of 40 to 100 burns over 180 to 360 degrees. These eyes had shown an excellent prolonged response to initial laser trabeculoplasty. Eight of 11 eyes with greater than one year follow-up showed a sustained hypotensive response to repeat laser trabeculoplasty. No significant posttreatment intraocular pressure increases were observed. Repeat argon laser trabeculoplasty was effective for these patients who had shown a prolonged response to their initial treatment.

Ocular inflammatory effects of intravitreally-injected tumor necrosis factor

Many of the pathophysiologic effects of bacterial endotoxin have recently been attributed to a monokine, tumor necrosis factor (TNF). The rabbit eye is extremely sensitive to locally injected endotoxin. The authors have investigated the possible contribution of TNF to ocular inflammation in a rabbit model. The intravitreal injection of 10(5) to 5 X 10(5) units of recombinant human TNF produced a sustained disruption of the blood-aqueous barrier as manifested by elevated aqueous humor protein levels. In addition, 83% of rabbits receiving this dose of TNF developed hyperemia of limbal vessels and early neovascularization of the cornea. Many developed posterior synechiae (fibrous adhesions between the iris and the lens). TNF induced only a slight cellular response in the anterior chamber. Histologic studies confirmed the presence of new vessels and demonstrated a marked mononuclear infiltrate within and beneath the epithelium of the iris and ciliary body. Lower doses of TNF produced inconsistent results. Heating TNF completely destroyed its inflammatory effects. The time course of the ocular response to TNF and the quantity of recombinant protein needed to produce consistent effects were vastly different from effects observed with interleukin-1. For example, 24 hours after an intravitreal injection, 2.2 X 10(4) ng of TNF (5 X 10(5) units) produced significantly less protein extravasation and polymorphonuclear leukocyte infiltration than 4 ng of recombinant interleukin-1. Similarly, 24 hours after intravitreal injection, 1 ng of Escherichia coli endotoxin tended to be a more potent inflammatory stimulus than this quantity of TNF. These observations indicate that the ocular pathophysiologic effects of TNF can be readily distinguished from changes induced by either endotoxin or another endotoxin induced monokine, interleukin-1.

Prostaglandin-independent inhibition of ocular vascular permeability by a platelet-activating factor antagonist

Platelet-activating factor (PAF), a lipid mediator of inflammation, may markedly increase vascular permeability. We assessed the ability of the PAF antagonist SRI 63-441 to inhibit ocular vascular permeability induced by the intravenous injection of endotoxin or anterior chamber paracentesis. The PAF antagonist SRI 63-441 significantly blocked ocular vascular permeability following either intravenous endotoxin or anterior chamber paracentesis as determined by the reduction in accumulation of 70,000-molecular-weight fluorescein isothiocyanate-conjugated dextran or serum proteins into the anterior chamber. SRI 63-441 did not reduce increases in aqueous humor prostaglandin E2 levels. The efficacy of the PAF antagonist was additive in combination with either topical indomethacin or topical corticosteroid. Combined therapy almost completely prevented increases in ocular vascular permeability. These data support the conclusion that multiple mediators contribute to ocular vascular permeability and that combinations of pharmacologic agents may be superior to a single drug.

Effect of melatonin on intraocular pressure

We studied the effect of orally administered melatonin on intraocular pressure in humans. We suppressed serum melatonin levels by exposing our subjects to bright light. Our experiments suggest that melatonin lowers intraocular pressure in man. This may prove to be a therapeutically useful agent since melatonin appears to be relatively free of side effects and is effective in small quantities.

Trabecular cell division after argon laser trabeculoplasty

The usefulness of argon laser trabeculoplasty (ALT) in the treatment of some patients with glaucoma has been established; yet, the mechanism of ALT is not understood. The hypothesis that the mechanism involves trabecular cell division was examined. Autoradiographic assessment of tritiated thymidine incorporation into trabecular cell DNA in a human corneoscleral explant organ culture system demonstrated a basal level of DNA replication that increased by 180% in the two days immediately after ALT. When labeling was initiated five days after ALT, DNA replication declined to 70% of the control level. The autoradiographic findings were confirmed using biochemical evaluation of tritiated thymidine incorporation into acid-precipitable macromolecules (DNA) in excised trabecular meshwork. One biologic response of the trabecular meshwork after laser trabeculoplasty is a change in the level of ongoing trabecular cell division.

A technique for removal of filariasis of the anterior chamber

We describe a useful technique for removing filaria from the anterior chamber. In the case described, an immature female filaria approximately 15 mm in length was removed from the anterior chamber of a 32-year-old man in western Oregon and identified as a species of Dipetalonema. Features of four cases of filarial infection in the anterior chamber from the same geographic area are described. In three out of four cases, the worms were removed alive without difficulty by means of simple irrigation aspiration system.

Human trabecular meshwork organ culture: morphology and glycosaminoglycan synthesis

Human corneoscleral explants were maintained for several weeks in defined, serum-free media. Trabecular cell vitality, as judged by vital stain exclusion, is high for at least one month. Trabecular ultrastructure, as compared to that of fresh eyes, first shows minor cellular and extracellular matrix degradation after 3 weeks in culture. The biosynthetic profiles of trabecular glycosaminoglycans (GAGs) change significantly by 3 weeks in culture. Eyes that are stored at 5 degrees C for up to 48 hr postmortem exhibit changes in trabecular ultrastructure and in GAG profiles; both characteristics return to normal by 7 days in culture. The incorporation pattern of 35S-sulfate and 3H-glucosamine into the GAGs of the trabecular meshwork (TM) is distinct from corneal or scleral incorporation. The relative incorporation of 3H-glucosamine into trabecular GAGs, as determined by sequential enzymatic degradation, is: 22.3% hyaluronic acid (HA), 27.9% chondroitin sulfate (CS), 21.3% dermatan sulfate (DS), 5.9% keratan sulfate (KS), 17.7% heparan sulfate (HS) and 4.9% unidentified material. The relative incorporation of 35S-sulfate into trabecular GAGs is: 0% HA, 32.9% CS, 34.8% DS, 7.7% KS, 13.8% HS and 11.1% into unidentified material. This profile is in good agreement with the profile that was previously obtained for human and nonhuman primate meshworks prior to culture. We conclude that corneoscleral explant organ culture is a useful tool for extracellular matrix studies within a time window from 7 to at least 14 days in culture.

Chemotactic activity of lens proteins and the pathogenesis of phacolytic glaucoma

Leakage of lens proteins from a hypermature cataract can result in a characteristic glaucoma that is associated with the invasion of the anterior chamber by monocytes. We hypothesized that the lens proteins themselves might account for the monocyte response. A sonicated lens induced concentration-dependent migration of monocytes in a Boyden chamber assay system. Checkerboard analysis indicated that the movement was directed rather than merely random. Relative to a control chemoattractant, N-formyl-methionyl-leucyl-phenylalanine, the lens induced monocyte migration more potently than neutrophil migration. The ability to induce migration was markedly reduced by incubating the lens with either trypsin or papain. Chemotactic activity was readily demonstrable in lenses from young donors without cataracts. Separation of lens proteins by gel filtration with high-performance liquid chromatography indicated that the chemotactic activity was most consistently associated with the gamma crystallin fraction. The chemotactic activity of lens proteins may contribute to the pathogenesis of phacolytic glaucoma or the uveitis resulting from retained cortical material after cataract extraction.

Ocular inflammatory effects of intravitreal interleukin 1

Locally injected endotoxin induces potent inflammatory changes in the rabbit eye. To clarify the possible role of interleukin 1 (Il-1), an endotoxin-induced monokine, in rabbit eye inflammation, we injected rabbits with recombinant Il-1 (rIl-1). Twelve and a half to 200 U of intravitreally injected rIl-1 consistently induced inflammation, which was documented using slit-lamp biomicroscopy, histologic methods, or direct quantitation of protein in the aqueous humor. Responses including a cellular infiltrate in the anterior chamber, protein extravasation, and iris vessel dilatation became evident within six hours, peaked at 24 hours, and began to recede by 48 to 72 hours after the injection. Pathologic changes primarily occurred in the anterior chamber and included edema, hemorrhage, and cellular infiltration. Locally injected corticosteroid reduced but did not prevent rIl-1-induced changes in vascular permeability. Heat-inactivated rIl-1 induced minimal changes, as determined by histologic methods, slit-lamp examination, or direct protein measurement. These data support the conclusion that Il-1 should be considered as a potential mediator of ocular inflammation.

Three-year efficacy of argon laser trabeculoplasty

The authors report on the effect of argon laser trabeculoplasty on intraocular pressure (IOP) over a 3-year period with a mean follow-up period of 1.8 years in patients with uncontrolled primary open-angle glaucoma who had not undergone prior surgery. An analysis of the effect of laser trabeculoplasty using the criteria for success of an IOP of 22 mmHg or less with no further laser trabeculoplasty or glaucoma surgery, showed a cumulative success of 79% (112 eyes) at 1 year, 69% (85 eyes) at 2 years, and 59% (58 eyes) at 3 years. Similar results are presented for 22 eyes from patients with pseudoexfoliation glaucoma. The authors conclude that although the initial success rate of laser trabeculoplasty is high, it diminishes progressively over time.

The corneal endothelium after laser therapy for glaucoma

Using computer assisted morphologic analysis of central corneal endothelial specular micrographs, we prospectively examined the effects of glaucoma laser procedures on the corneal endothelium. Argon laser trabeculoplasty was performed in 22 eyes of 17 patients. Argon laser iridotomy was performed in 14 eyes of seven patients. Untreated fellow eyes in ten patients undergoing laser trabeculoplasty were used as controls. After one year, no statistically significant difference in cell area, percent hexagonal cells, or shape factor was observed. Our results suggest that argon laser procedures do not pose any long-term hazard to the corneal endothelium.

Chemotactic activity in aqueous humor from patients with anterior uveitis

Anterior uveitis, inflammation of the iris or ciliary body of the eye, may be associated with a variety of systemic diseases. Although a leukocytic infiltrate is characteristic of anterior uveitis, few studies have sought to detect factors in aqueous humor that could attract neutrophils or monocytes into the anterior chamber. Using modified Boyden chambers, we found that a 5% concentration of aqueous humor from patients with anterior uveal inflammation induced monocyte movement comparable to optimal or near-optimal concentrations of C (complement)5a or platelet-derived growth factor. Aqueous humor from patients with anterior uveitis induced significantly more monocyte migration than did aqueous humor from two sets of controls (either patients undergoing cataract extraction or patients with posterior uveitis). "Checkerboard" or gradient analysis indicated that a majority of inflammatory disease samples induced monocyte chemotaxis (directed migration) while the control aqueous humor consistently induced chemokinesis (stimulated random migration) (P less than 0.02). Despite their ability to induce monocyte migration, samples tended to induce minimal neutrophil migration with the exception of aqueous humor that was obtained from one patient with acute anterior disease. This sample induced marked chemokinesis. Identification of chemotactic activity may clarify the pathogenesis of uveitis and the characterization of leukocyte migration factors in aqueous humor may help define subsets of anterior uveal inflammation.