Influence of autonomic neurotransmitters on human uveal melanocytes in vitro

Effects of Toll-like receptor 1 and 2 agonist Pam3CSK4 on uveal melanocytes and relevant experimental mouse model

Pam3CSK4 activates Toll-like receptors 2 and 1 (TLR1/2), which recognize mainly molecules from gram-positive pathogens. The effect of Pam3CSK4 on various cytokine and chemokine expression in cultured human uveal melanocytes (UM) has not been studied systematically. The purpose of this study was to investigate the mechanistic expressions of seven cytokines and chemokines of interleukin- (IL-) 6, IL-10, MCP-1 (CCL-2), CXCL-1 (GRO-α), CXCL-8 (IL-8), interferon-gamma (IFN-γ), and tumor necrosis factor-alpha (TNF-α) in UM. These cytokines are reported to be increased in intraocular fluids or tissues of the patients with endophthalmitis and non-infectious uveitis, as well as in various experimental animal uveitic models in the literature. Flow cytometry was used to measure the effects of Pam3CSK4 on the expression of TLR1/2 in UM. ELISA and Real-time PCR analysis were used to estimate the ability of Pam3CSK4 to elevate these cytokines and chemokines levels in conditioned media and cell lysates of UM, respectively. Flow cytometry measured and compared the phosphorylated MAPK pathway and activated NF-κB signals pathway in UM, treated with and without Pam3CSK4. ELISA analysis tested the effect of various signal inhibitors (ERK1/2, JNK1/2, p38 and NF-κB) on Pam3CSK4-induced IL-6 levels in cultured UM. The role of TLR2 in Pam3CSK4-induced acute anterior uveitis in experimental mouse model was tested in TLR2 knockout (TLR2 KO) mice and their wild-type C57Bl/6 controls. Pam3CSK4 increased the expression of TLR1/2 proteins in cultured UM. Pam3CSK4 significantly elevated the IL-6, MCP-1, CXCL-1, CXCL-8 protein, and mRNA levels in cultured UM, but not IL-10, TNF-α, or IFN-γ. Pam3CSK4 activated NF-κB, ERK, JNK, and p38 expression. Pam3CSK4-induced expression of IL-6 was decreased by NF-κB, ERK, INK, and p38 inhibitors; especially the NF-κB inhibitor, which can completely block the IL-6 stimulation. Intravitreal injection of Pam3CSK4 induced acute anterior uveitis in C57Bl/6 mice, this effect was significantly reduced in TLR2 KO mice. TLR1/2 plays an important role against invading pathogens, especially gram-positive bacteria; but an excessive reaction to molecules from gram-positive bacteria may promote non-infectious uveitis. UM can produce IL-6, MCP-1, CXCL-1, and CXCL-8, and are one of the target cells of TNF-α and IFN-γ. TLR-2 inhibitors might have a beneficial effect in the treatment of certain types of uveitis and other ocular inflammatory-related diseases and warrant further investigation.

Dispositional mindfulness and BIS/BAS up-close: can the self-regulation of people be seen in the eyes?

Introduction

Pigmentation in animal models is related to behavioral regulation and development, suggesting that both may belong to the same biological system. However, such models are poorly documented in humans. The current study explored personality and group differences in self-regulation among healthy subjects and their specific eye structures (contraction furrows and pigment spots). Three objectives were proposed: to analyze statistical differences in dispositional mindfulness (DM), behavioral inhibition system (BIS), and behavioral approach system (BAS) among subjects with a specific iris type of contraction furrows and pigment spots.

Methods

The study sample consisted of 194 university students. One month after taking photographs of their eyes, the students completed the online scales of DM, BIS, and BAS.

Results

DM was negatively related to pigment spots (rs = -0.193; p < 0.01). Cluster analysis of the iris structures converged at a four-cluster solution. The cluster types 2 (absence of pigment spots and contraction furrows extending 8/10 of iris circle or more) and 3 (one or more pigment spots and contraction furrows extending 8/10 of iris circle or more) significantly differed in DM with a small effect size (F = 3.37; p = 0.021; η2 = 0.051). Participants with contraction furrows (8/10 or more circle extent) and without pigment spots had a significantly higher DM than those with pigment spots. No significant differences existed among the iris types in BIS/BAS.

Discussion

Future research directions are suggested.

Excretion and Residual Concentration Correlations of Salbutamol Between Edible Tissues and Living Samples in Pigs and Goats

Illegal use of salbutamol (SAL), a β-adrenergic leanness-enhancing agent, has posed potential threat to human health in China. The excretion and depletion of SAL in pigs and goats were investigated, and the concentration correlations between edible tissues and living samples were analyzed to find out a suitable living sample for pre-slaughter monitoring of SAL in pigs and goats. After a single oral dosage of 1.2 mg/kg SAL, approximately 70% of the dose was excreted by pigs and goats from their excreta. When pigs and goats were supplied feed containing SAL (20 mg/kg) for 14 consecutive days, high concentrations of SAL were observed in the liver and kidneys, and the longest persistence was observed in hair. Unlike pigs, SAL was presented primarily as conjugated SAL in goats. Excellent concentration correlations of SAL were observed between urine and edible tissues both in pigs and goats, and in addition, good correlations also were found between hair and edible tissues in pigs and between feces and edible tissues in goats. Hence, urine and hair could accurately predict SAL concentrations in edible tissues of pigs, whereas feces and urine were satisfactory for predicting SAL concentrations in edible tissues of goats. These data make it possible for pre-slaughter monitoring of SAL residues in the edible tissues of pigs and goats.

Quantitative Study of Human Scleral Melanocytes and Their Topographical Distribution

PURPOSE

While fibroblasts constitute the main cell component of the sclera, the purpose of the present study was to investigate the cell densities of melanocytes at different regions of the sclera, and to compare them with associated scleral fibroblast densities in human donor eye sections.

METHODS

. Paraffin-embedded sections of sclera from 21 human eyes were stained with hematoxylin-eosin (H&E) and immunohistochemical staining (S-100/AEC). Scleral melanocyte and fibroblast numbers were counted in different regions of the sclera. The relationship between the melanocyte density and iris pigmentation was also analyzed.

RESULTS

. Melanocytes were found in the posterior region of the sclera, especially around the vessels and nerves in emmissarial canals, whereas no or rare melanocytes were found in equatorial and anterior regions. In H&E sections, melanocyte densities in eyes with light-colored irides were significantly less than in eyes with medium or dark-colored irides (P < .05). In S-100-stained sections, more melanocytes could be detected than those in the H&E sections in light-colored eyes (P < .05), but not in medium or dark-colored eyes (P > .05). The numbers of scleral fibroblasts were relatively stable in different regions. In the posterior scleral region, the numbers of fibroblasts were slightly higher than the number of melanocytes, however, this differences were not statistically significant (P > .05).

CONCLUSION

. Notable numbers of melanocytes were present in the posterior sclera suggesting that these cells may play a role in ocular physiology and in the pathogenesis of various disorders of the sclera.

Beta-adrenergic agonist protects retinal pigment epithelium against hydroxycholoroquine toxicity via cAMP-PKA signal pathway

AIM

To test our hypothesis that activation of protein kinase A (PKA) signal pathway by β-adrenergic agonist plays an important role in the protecting of cultured retinal pigment epithelial (RPE) cells against the hydroxychloroquine (HCQ) toxicity.

METHODS

Cultured human RPE cells were treated with 1) HCQ, 2) HCQ with salbutamol (a β2-adrenergic receptor agonist), and 3) HCQ with salbutamol and a PKA inhibitor, and compared these to 4) untreated cells (controls). After treated for 24h, cell vacuolation, cells viability, PKA and PKA kinase activity levels were determined by the measurement of the size of vacuoles using Image J software, the cell counting with a dye-exclusion testing, Western blot and PKA kinase detection, respectively.

RESULTS

Cell vacuolation and cell death of cultured RPE cells were significantly increased by the treatment of HCQ. Salbutamol significantly elevated PKA and PKA activity levels and this was associated with the inhibition of the vacuolation and cell death. The PKA inhibitor significantly decreased the PKA levels and eliminated the protective effects of salbutamol on HCQ-treated RPE cells.

CONCLUSION

The PKA pathway plays an important role in the protective effects of β2-adrenergic agonist on the RPE cells against HCQ toxicity. These findings reveal a novel potential strategy against HCQ retinopathy by treatment with PKA activating medications.

Human choroidal melanocyte signal transduction responses to various pharmacological agents: focus on endothelin receptors

PURPOSE

The receptor-coupled signal transduction systems present in isolated human choroidal melanocytes (HCOMs) were investigated.

METHODS

[(3)H]-inositol phosphates ([(3)H]-IPs) generated in the cells were measured by ion-exchange chromatography. cAMP generated in the cells was quantified using an enzyme immunoassay.

RESULTS

Initially, HCOM cells were challenged with a relatively high concentration (e.g., 1 µM-1 mM) of a variety of pharmacological agents in order to determine which functional receptors were present in these cells. Full concentration-response pharmacological studies were subsequently conducted on endothelin receptors. While a number of prostaglandins (PGs) (e.g., PGD(2), PGE(2), PGF(2α), cloprostenol, latanoprost acid, U-46619), histamine, carbachol, bombesin, and arginine-vasopressin were essentially inactive at stimulating the phosphoinositide (PI) hydrolysis response, endothelin-1 (ET-1) potently and efficaciously generated [(3)H]-IPs. Concentration-response studies yielded the following potency (EC(50)) and efficacy (E(max) relative to ET-1) data: ET-1 EC(50) = 3.4 ± 1.4 nM, E(max) = 100%, n = 3; BQ-3020 (ET(B) receptor-selective agonist) EC(50) = 13 ± 4 nM, E(max) = 73 ± 2%, n = 3). The effects of ET-1 on [(3)H]-IPs production were blocked by the ET(B) receptor-selective antagonist, BQ-788 (IC(50) = 10 ± 5 nM, n = 3), while the ET(A) receptor-selective antagonist (BQ-610) was essentially inactive. In the adenylyl cyclase (AC) assay, while isoproterenol (10 µM), ET-1 (1 µM) and PGE(2) (10 µM) stimulated cAMP production, numerous other PGs (e.g., PGD(2), PGF(2α), PGI(2), latanoprost, latanoprost acid, U-46619 and BW245C [all at > 10 µM]) were inactive.

CONCLUSIONS

It is concluded that HCOMs express functionally active ET(B) receptors that mediate the production of [(3)H]-IPs. Additionally, HCOMs generate cAMP in response to ET-1, PGE(2), and isoproterenol. These data may have relevance to the melanogenic activity of HCOM cells.

Intracellular signaling in human iridial fibroblasts and iridial melanocytes in response to prostaglandins, endothelin, isoproterenol, and other pharmacological agents

PURPOSE

The receptor-coupled signal transduction systems present in isolated human iridial fibroblasts (HIF) and in human iridial melanocytes (HIM) were investigated. Cell responsiveness to numerous prostaglandins (PGs), and other compounds of interest, was profiled in order to better understand their involvement in the iridial hyper-pigmentation process observed during treatment of elevated intraocular pressure with FP-receptor against PG analogs.

METHODS

[(3)H]-inositol phosphates ([(3)H]-IPs) generated in the cells were measured by ion-exchange chromatography followed by liquid scintillation spectroscopy. cAMP generated in the cells was quantified using an enzyme immunoassay.

RESULTS

HIF cells exhibited a robust phosphoinositide (PI) hydrolysis response to FP-class PG analogs, such as cloprostenol (potency, EC(50) = 2.4 ± 0.5 nM, n = 5), fluprostenol (EC(50) = 5.3 ± 0.6 nM, n = 3), PGF(2α) (EC(50) = 54 ± 18 nM, n = 5), and latanoprost acid (EC(50) = 121 ± 17 nM, n = 4). Other PGs exhibited the following potencies (EC(50)) for stimulating [(3)H]-IPs accumulation in HIF cells: PGD(2) EC(50) = 327 ± 195 nM, n =3; PGE(2) EC(50) = 550 ± 50 nM, n = 3; and two TP-receptor agonists (I-BOP, EC(50) = 23 ± 8 nM, n = 3; U-46619 EC(50) = 1.1 ± 0.4 µM, n = 3). Endothelin-1 (ET-1) and histamine increased [(3)H]-IPs production in HIF and HIM cells. HIM cells exhibited minimal PI turnover response to cloprostenol, latanoprost acid, latanoprost, PGF(2α), PGE(2), and histamine, but there were robust responses to ET-1 (EC(50) = 4.6 nM, n = 2) and an ET(B)-receptor agonist (BQ-3020, EC(50) = 5 nM, n = 2) that were blocked by an ET(B)-antagonist (BQ-788, IC(50) = 21 ± 6 nM, n = 3). In the adenylyl cyclase activation assay, numerous PGs (1 and 10 µM) stimulated cAMP production in HIF cells yielding the following rank order of efficacy: PGI(2) > PGE(2) > misoprostil > isoproterenol = BW245C > PGD(2) = PGF(2α) = fluprostenol. In HIM cells, PGE(2) (EC(50) = 1.3 ± 0.3 nM) and isoproterenol (β-agonist; EC(50) = 89 ± 13 nM) potently and efficaciously stimulated cAMP production and ICI-118851 (β(2)-antagonist) attenuated the effects of isoproterenol. However, latanoprost acid, latanoprost, ET-1, and BW245C (DP-receptor agonist) were relatively less efficacious than isoproterenol and PGE(2) in HIM cells at stimulating cAMP production.

CONCLUSIONS

These studies have shown that while HIF cells express FP prostaglandin and histamine receptors coupled to phospholipase C to produce [(3)H]-IPs, the HIM cells lack such functionally active FP-receptors. In contrast, HIF and HIM cells express functional ET-1 receptors coupled to [(3)H]-IPs production and both cell-types respond to PGE(2), BW245C, and isoproterenol by generating cAMP. It is concluded that human iridial fibroblasts and melanocytes respond differently to PGs and histamine, but in the same manner to ET-1, isoproterenol and BW245C. This may have relevance to the intercellular communication within the iris relative to the melanogenic processes.

An in vivo model of melanoma: treatment with ATP

Athymic mice, injected with A375 human melanoma cells, were treated daily with intraperitoneal injections of adenosine 5'-triphosphate (ATP). The tumour volume and animal weight were measured over the course of the experiment and the final tumour nodule weight was measured at the end of the experiment. Tumour volume decreased by nearly 50% by 7 weeks in treated mice. Weight loss in untreated animals was prevented by ATP. Histological examination of the excised tumour nodules showed necrosis in the ATP-treated tumours only. The presence of P2Y(1) and P2X(7) receptors, previously proposed as extracellular targets for melanoma treatment with ATP, were demonstrated in the excised specimens by immunohistochemistry. This paper provides further support for the use of ATP as a treatment for melanoma.

Methodology for evaluation of melanin content and production of pigment cells in vitro

Melanin has a photo-screening, a biophysical/biochemical and a cosmetic effect. Melanin content of cultured pigmented cells can be measured by spectrophotometry and expressed either as melanin content per cell or melanin content per culture (area). Melanin production can be calculated from melanin content and cell number at the beginning and at the end of a culture using various formulas and expressed as melanin production per cell per day or melanin production per culture per day. Melanin content or production per cell have been used widely to compare melanin content in various cell lines or to compare the melanin content during different stages in the culture (e.g. growing stage and senescent stage). For the evaluation of changes in melanin content and production in a given pigment cell line after treatment with a special chemical, physical or biological stimulator or inhibitor, different parameters used for the evaluation of experimental data can lead to conflicting results. Melanin content per area is determined by melanin content per cell and the number of cells in this area. The biological and cosmetic effects of melanin in vivo are determined mainly by melanin content per area, not melanin content per cell. For example, if melanin content per cell is the same, but the number of cells in a given area is increased after the treatment, then the melanin content per area is also increased. Under this circumstance, the color of skin turns darker and the total antioxidant activity provided by melanin in this area is increased even though the melanin content per cell measured remains the same; therefore, melanin content or production per culture is more important than melanin content or production per cell under this circumstance.

Associations between iris characteristics and personality in adulthood

Variable and person-oriented analyses were used to explore the associations between personality and three previously untested general iris characteristics: crypts, pigment dots and contraction furrows. Personality data, as measured by the NEO PI-R and ratings of iris characteristics from 428 undergraduate students were collected. Crypts were significantly associated with five approach-related behaviors, i.e., feelings, tendermindedness, warmth, trust and positive emotions, whereas furrows were associated with impulsiveness. These findings suggest that because Pax6 induces tissue deficiencies in both the iris and the left anterior cingulate cortex, Pax6 may influence the extent people engage in approach-related behaviors. The results from using a person-oriented analysis suggested that people with different iris configurations tend to develop along different personality trajectories. Future longitudinal studies, twin-studies and genetic association studies, may benefit from collecting iris data and testing candidate genes for crypts and furrows.

Serum-free cultivation of adult normal human choroidal melanocytes

BACKGROUND

Cultures of normal choroidal melanocytes are useful in vitro models for the study of melanocyte biology. Current protocols involve the supplementation of culture media with serum, toxins, and phorbol esters, the latter being known as tumour-inducing agents. We therefore sought to establish a protocol to cultivate normal human choroidal melanocytes (NHCMs) without these supplements.

METHODS

NHCMs were isolated by dispase II treatment, after isolation of retinal pigment epithelial (RPE) cells, and seeded in serum-free Melanocyte Growth Medium M2 in uncoated T25 cell culture flasks. Purity of the established cultures was proven by immunocytochemistry. Morphology of the cultured cells was evaluated throughout the entire cultivation period. Eventually, cells were cryopreserved in liquid nitrogen.

RESULTS

The cultures underwent at least 11.5 +/- 4.5 doublings before they became senescent or culture was deliberately terminated. Mean generation time was 95.0 +/- 27.7 h. After cryopreservation, generation time was markedly increased, but proliferative capacity of the cells was not impaired. Cultured cells showed bipolar to dendritic morphology; sometimes flattened triangular cells were seen in the cultures. Cultured cells lost pigment after initial seeding but displayed continuous melanogenesis. All cultures stained positive for HMB45 antigen and S-100 and negative for RPE-specific cytokeratins 8, 18. Only few cultures contained single cells that were weakly positive for matrix metalloproteinase (MMP)-2 or MMP-9.

CONCLUSIONS

The cultivation protocol yields pure cultures of NHCMs that can successfully be maintained for several months without the use of serum, tumour-inducing substances, or toxins.

Isolation, purification and cultivation of conjunctival melanocytes

The purpose of the present study was to develop methods for isolation, purification and cultivation of human conjunctival melanocytes. Conjunctiva excised from donor eyes or corneal rims was subjected with various enzyme digestion methods or by the enzyme-microdissection method. Cells were cultured with F12 medium supplemented by fetal bovine serum, basic fibroblast growth factor, isobutylmethylxanthine and cholera toxin. Contaminant cells were eliminated by a selective cytotoxic agent, geneticin. Both trypsin digestion and dispase-microdissection methods provided pure conjunctival melanocyte cultures with high cell yields, good viability and rapid growth rate. Melanocytes isolated with dispase-microdissection method showed better viability and growth capacity. Cells grew well, could be passaged for 5-10 generations and divided 20 times in vitro. They maintained a constant melanin content per cell and produced measurable amounts of melanin in vitro. Melanogenesis correlated with the degree of pigmentation of the eyes (iris color). This method provides a valuable source of large numbers of human conjunctival melanocytes, which can be used to study their biological behavior, to compare with the epidermal and uveal melanocytes; and to compare them to their malignant counterparts in the exploration of the pathogenesis of conjunctival melanoma.

Uveal Melanocytes Produce Matrix Metalloproteinases-2 and -9 In Vitro

The purpose of the present study was to investigate the expression of matrix metalloproteinase (MMP)-2 and MMP-9 by cultured human uveal melanocytes, and to test the effects of 12-O-tetradecanoyl-phorbol-13-acetate on the expression of these MMPs. Gelatin zymography of conditioned culture medium from four cultures of human uveal melanocytes (two cultures of iridal melanocytes and two cultures of choroidal melanocytes) detected MMP-2 (72 kDa) and a relatively small amount of MMP-9 (92 kDa), both in the latent form. RT-PCR analysis revealed the MMP-2 mRNA and MMP-9 mRNA in cultured uveal melanocytes. Addition of 12-O-tetradecanoyl-phorbol-13-acetate (10 ng/ml) to the culture medium caused an increase of production of MMP-2 and MMP-9 by cultured uveal melanocytes, and also stimulated the transcription of MMP-2 and MMP-9 of these cells.

Tissue plasminogen activator is released into cultured medium by cultured human uveal melanocytes

Melanoma cells produce tissue plasminogen activator (t-PA) that plays an important role in tumor invasion and metastasis. The production of t-PA by normal human uveal melanocytes has not been reported previously. In order to explore this possibility, we studied the production of t-PA by cultured human uveal melanocytes and compared that with the production by cultured human uveal melanoma cells and epidermal melanocytes. Human adult uveal melanocytes were isolated and cultured from donor eyes. The cells were cultured in serum-free medium for 48 h and the conditioned medium then collected for the plasminogen activator (PA) activity assay. Free PA activity was tested in an amidolytic assay using a t-PA standard curve. PA type was identified by fibrinography and antihuman t-PA and urokinase plasminogen activator (u-PA) blocking antibodies. Free PA activity was found in the conditioned medium of normal melanocytes and melanoma cells. The predominant PA activity was t-PA. Normal uveal melanocytes produced more t-PA (3.23 +/- 0.73 IU/105 cells/24 h) than that of epidermal melanocytes (1.25 IU/105 cells/24 h) but much less than uveal melanoma cells (11.0 +/- 3.39 IU/105 cells/24 h). Western blot analysis revealed that most t-PA in conditioned media were one-chain t-PA with molecular weight of 69 kDa. Our study indicates that uveal melanocytes may contribute to the free t-PA activity previously found in aqueous humor and choroidal eye cup superfusions. Therefore, this function of uveal melanocytes may play a role in intraocular matrix remodeling, fibrinolysis and aqueous humor outflow.

Production of prostaglandin e(2) by iridial melanocytes exposed to latanoprost acid, a prostaglandin F(2 alpha) analogue

Several prostaglandin analogues used for glaucoma treatment cause increased pigmentation of the iris. The purpose of the present study was investigate whether latanoprost, a PGF(2 alpha) analogue, has any effect on the production of endogenous prostaglandins in iridial melanocytes, which could be important in the mechanism leading to increased pigmentation. Bovine and human iridial melanocytes in culture were used for the experiments. Production of endogenous prostaglandins was measured by enzyme immunoassay, and the melanin content was measured spectrophotometrically. In bovine iridial melanocytes, latanoprost acid caused a significant increase of the PGE(2) production, which could be blocked by indomethacin and NS398, indicating an involvement of cyclo-oxygenase 2. In order to study the selectivity of the phenomenon other endogenous substances/drugs were tested, e.g., acetylcholine, carbachol, noradrenaline, neuropeptide Y, substance P and alpha-MSH, but none was found to have any significant effect. Human iridial melanocytes also responded to latanoprost acid with increased production of PGE(2) and in 1 out of 5 individuals increased melanogenesis coincided with increased PGE(2) production. In bovine iridial melanocytes, latanoprost acid did not stimulate melanogenesis. These results indicate that latanoprost acid cause enhanced formation of endogenous prostaglandins that may have auto- and/or paracrine effects in the melanocytes, possibly associated with melanogenesis.

Mechanism and clinical significance of prostaglandin-induced iris pigmentation

The new glaucoma drugs latanoprost, isopropyl unoprostone, travoprost, and bimatoprost cause increased pigmentation of the iris in some patients. The purpose of the present article is to survey the available preclinical and clinical data on prostaglandin-induced iris pigmentation and to assess the phenomenon from a clinical perspective. Most of the data have been obtained with latanoprost, and it appears that there is a predisposition to latanoprost-induced iris pigmentation in individuals with hazel or heterochromic eye color. As latanoprost and travoprost are selective agonists for the prostaglandin F(2alpha) receptor, it is likely that the phenomenon is mediated by this receptor. Several studies indicate that latanoprost stimulates melanogenesis in iridial melanocytes, and transcription of the tyrosinase gene is upregulated. The safety aspects of latanoprost-induced iris pigmentation have been addressed in histopathologic studies, and no evidence of harmful consequences of the side effect has been found. Although a final assessment of the clinical significance of prostaglandin-induced iris pigmentation currently is impossible to make, it appears that the only clear-cut disadvantage is a potential heterochromia between the eyes in unilaterally treated patients because the heterochromia is likely to be permanent, or very slowly reversible.

The iris after prostanoid treatment

Morphologic studies to date show that prostanoid-induced iris color change is not associated with any major pathologic process in the tissue. There is no evidence of melanocyte proliferation. The most likely mechanism for iris color darkening is increased melanogenesis, but this is not so marked as to cause any extensive release of melanin granules that might cause iris inflammation or even a pigmentary-type of glaucoma. Some patients, but not all, with color darkening have an apparent thickening of the anterior border zone; it remains to be established whether this is true thickening or merely if the anterior border is emphasized because of increased pigmentation.