The genetics and evolution of eye color in domestic pigeons (Columba livia)

The eye color of birds, generally referring to the color of the iris, results from both pigmentation and structural coloration. Avian iris colors exhibit striking interspecific and intraspecific variations that correspond to unique evolutionary and ecological histories. Here, we identified the genetic basis of pearl (white) iris color in domestic pigeons (Columba livia) to explore the largely unknown genetic mechanism underlying the evolution of avian iris coloration. Using a genome-wide association study (GWAS) approach in 92 pigeons, we mapped the pearl iris trait to a 9 kb region containing the facilitative glucose transporter gene SLC2A11B. A nonsense mutation (W49X) leading to a premature stop codon in SLC2A11B was identified as the causal variant. Transcriptome analysis suggested that SLC2A11B loss of function may downregulate the xanthophore-differentiation gene CSF1R and the key pteridine biosynthesis gene GCH1, thus resulting in the pearl iris phenotype. Coalescence and phylogenetic analyses indicated that the mutation originated approximately 5,400 years ago, coinciding with the onset of pigeon domestication, while positive selection was likely associated with artificial breeding. Within Aves, potentially impaired SLC2A11B was found in six species from six distinct lineages, four of which associated with their signature brown or blue eyes and lack of pteridine. Analysis of vertebrate SLC2A11B orthologs revealed relaxed selection in the avian clade, consistent with the scenario that during and after avian divergence from the reptilian ancestor, the SLC2A11B-involved development of dermal chromatophores likely degenerated in the presence of feather coverage. Our findings provide new insight into the mechanism of avian iris color variations and the evolution of pigmentation in vertebrates.

Differences in FM100‐Hue test performance related to iris colour may be due to pupil size as well as presumed amounts of macular pigmentation

BACKGROUND

It has been reported that the differences in macular pigment between Asian and Caucasian eyes might give rise to different performance on the Farnsworth-Munsell 100 Hue test. However, the study did not appear to account adequately for the observation that differences were apparent only in older age groups. It was also acknowledged that other factors, like pupil size and crystalline lens colouration, could influence the result.

METHOD

We investigated the performance of the Farnsworth-Munsell 100 Hue test, under standard conditions, by three groups with presumed different macular pigmentation and narrow age range. We also measured pupil size.

RESULTS

The group with blue irides (presumed low macular pigmentation) performed significantly better on the colour vision task than the Asian group and the brown-eyed subjects as a whole (presumed higher macular pigmentation). In addition, the difference in pupil size between the blue-eyed group and brown-eyed groups bordered on significance. The difference in pupil size and consequential reduction in retinal illuminance account for a significant proportion of the difference in colour vision performance. In addition, a difference in both pupil size and Farnsworth-Munsell 100 Hue test performance was also observed between males and females that reinforced the importance of pupil size, and not just macular pigment, as a factor in colour vision performance difference between Asian and non-Asian eyes.

CONCLUSION

It is concluded that pupil size, not just macular pigment, may have a significant influence on colour vision performance in a young, healthy population.

Iris Colour and the Risk of Developing Uveal Melanoma

Uveal melanoma (UM) is a global disease which especially occurs in elderly people. Its incidence varies widely between populations, with the highest incidence among Caucasians, and a South-to-North increase in Europe. As northern Europeans often have blond hair and light eyes, we wondered whether iris colour may be a predisposing factor for UM and if so, why. We compared the distribution of iris colour between Dutch UM patients and healthy Dutch controls, using data from the Rotterdam Study (RS), and reviewed the literature regarding iris colour. We describe molecular mechanisms that might explain the observed associations. When comparing a group of Dutch UM patients with controls, we observed that individuals from Caucasian ancestry with a green/hazel iris colour (Odds Ratio (OR) = 3.64, 95% Confidence Interval (CI) 2.57-5.14) and individuals with a blue/grey iris colour (OR = 1.38, 95% CI 1.04-1.82) had a significantly higher crude risk of UM than those with brown eyes. According to the literature, this may be due to a difference in the function of pheomelanin (associated with a light iris colour) and eumelanin (associated with a brown iris colour). The combination of light-induced stress and aging may affect pheomelanin-carrying melanocytes in a different way than eumelanin-carrying melanocytes, increasing the risk of developing a malignancy.

Residual Iris Retraction Syndrome After Artificial Iris Implantation

PURPOSE

To evaluate the effect of an artificial iris implant on the remnant iris.

DESIGN

Interventional case series.

METHODS

Setting: Single center.

PATIENT POPULATION

Forty-two consecutive patients.

OBSERVATION PROCEDURES

Morphologic evaluation over 24 ± 14 months.

MAIN OUTCOME MEASURES

Remnant pupillary aperture, iris color, visual acuity, intraocular pressure, and endothelial cell count.

RESULTS

In 7 of 42 cases (16.7%), the residual iris aperture dilated from 36.6 ± 15.4 mm² preoperatively to 61.1 ± 12.5 mm² 1 year postoperatively (66.9% increase). In 5 of 7 affected eyes the artificial iris had been implanted into the ciliary sulcus; in 2 eyes it had been sutured to the sclera. Four of the 7 patients presented with remarkable complications: 2 eyes needed glaucoma shunt surgeries owing to pigment dispersion; 1 suffered from recurrent bleedings; and in 1 case artificial iris explantation was performed owing to chronic inflammation. Anterior chamber depth and angle, endothelial cell count, and visual acuity did not change in this cohort. Changes in color were not observed in the remnant iris.

CONCLUSIONS

The implantation of an artificial iris prosthesis can lead to a residual iris retraction syndrome. It is likely that residual iris is trapped in the fissure between the artificial iris and the anterior chamber angle, preventing further pupil constriction. Another possibility could be a constriction or atrophy of the residual iris. A scleral-sutured implant and an implantation in the capsular bag were both found to prevent the iris retraction. The study group number is inadequate to allow statistical comparison of these different implantation methods. As the use of artificial irises increases, we may expect more patients with iris retraction syndrome in the future.

Iris colour and astigmatism among Chinese teenagers

BACKGROUND/AIMS

Iris colour might contribute to refractive development, but it is uncertain whether it is related to astigmatism. We aim to examine the association of iris colour with the presence of astigmatism in a school-based sample of Chinese students.

METHODS

2346 grade 7 students from 10 middle schools aged 13 to 14 years in Southwestern China participated in the study. We obtained standardised slit-lamp photographs and developed a grading system assessing iris colour (higher grade denoting darker). Astigmatism was defined as a cylinder power of more than 0.50, 0.75 or 1.00 dioptre (D). Logistic regression models with generalised estimating equation were fitted to assess the relationship between iris colour and astigmatism, accounting for the correlation between both eyes. ORs and 95% CIs were presented.

RESULTS

The overall prevalence of astigmatism for three different definitions was 30.4% (95% CI 28.6% to 32.2%) (<-0.5 D), 12.7 % (95% CI 11.3% to 14.0%) (<-0.75 D) and 5.3% (95% CI 4.4% to 6.2%) (<-1.0 D), respectively. In multivariate analysis adjusting for the effect of gender and height, darker iris colour was associated with an increasing trend of astigmatism (p for trend <0.05). Compared with individuals with iris colour of grade 4 or 5 (the darkest), those with grade 1 or 2 (the lightest) were significantly less likely to be affected by astigmatism (<-0.75 D) in gender-adjusted model (OR 0.67) and multivariate-adjusted model (OR 0.72).

CONCLUSION

Darker iris colour might be a risk factor for astigmatism in Chinese adolescents.

Hyperspectral optical imaging of human iris in vivo: characteristics of reflectance spectra

We report a hyperspectral imaging system to measure the reflectance spectra of real human irises with high spatial resolution. A set of ocular prosthesis was used as the control condition. Reflectance data were decorrelated by the principal-component analysis. The main conclusion is that spectral complexity of the human iris is considerable: between 9 and 11 principal components are necessary to account for 99% of the cumulative variance in human irises. Correcting image misalignments associated with spontaneous ocular movements did not influence this result. The data also suggests a correlation between the first principal component and different levels of melanin present in the irises. It was also found that although the spectral characteristics of the first five principal components were not affected by the radial and angular position of the selected iridal areas, they affect the higher-order ones, suggesting a possible influence of the iris texture. The results show that hyperspectral imaging in the iris, together with adequate spectroscopic analyses provide more information than conventional colorimetric methods, making hyperspectral imaging suitable for the characterization of melanin and the noninvasive diagnosis of ocular diseases and iris color.

Influence of the photoperiod on growth rate and insulin-like growth factor-I gene expression in Nile tilapia Oreochromis niloticus

The effects of the duration of the light phase photoperiod (8 h light or 16 h light) on the growth and hepatic insulin-like growth factor-I (IGF-I) gene expression in Nile tilapia Oreochromis niloticus were evaluated. There was a slight but not significant tendency for fish in the long light phase group (L(P)) to display elevated specific growth rate (G) both in mass (M) and standard length (L(S)) compared with that in the short light phase group (S(P);P = 0.057 for G(M);P = 0.055 for G(L)). Significantly, higher food conversion efficiency was observed in the L(P) than in the S(P). There were significant positive correlations between IGF-I concentrations and G, both in M and L(S). A significantly negative correlation was observed between IGF-I mRNA level and eye colour pattern. The lack of significant differences in G and hepatic IGF-I gene expression, despite the significant difference in feed conversion efficiency, may be related partly to the development of different levels of social interactions in the different groups within a photoperiod regime leading to increased variation of results within each group. These findings suggest that hepatic IGF-I gene expression has potential utility as a growth rate indicator for this species of fish and social status, as quantified by eye colour pattern, appears to be a much stronger determinant of growth rate and IGF-I transcript level than does light phase photoperiod length.

[Association between iris color and ciliary body pigmentation: possible implications for cyclophotoablation treatment]

BACKGROUND

Cyclophotoablation for glaucoma treatment is dependent on the amount of laser energy absorbed by the ciliary body and related to the degree of its pigmentation. Iris color may be assessed by observing the eye, but it is unknown whether it correlates with ciliary body pigmentation.

AIM

We evaluated whether ciliary pigmentation correlates with iris color.

METHODS

The pigmented epithelium of the ciliary processes of 31 enucleated eyes was qualitatively scored for six histological parameters and correlated with iris color.

RESULTS

The dark iris group (n = 19) had significantly increased histological parameters of pigmentation such as aggregation of melanosomes, compared to the light iris group (n = 12) (p < 0.01).

CONCLUSION

Iris color correlates with ciliary pigmentation and may serve as one of the factors determining laser power needed for cyclophotoablation.

Reproductive fertility of cloned male cats derived from adult somatic cell nuclear transfer

This study was designed to investigate the reproductive fertility by the natural breeding of cloned male cats with domestic female cats, and to measure endocrine hormone concentration related to male reproduction such as testosterone, leutinizing hormone (LH), and follicle stimulating hormone (FSH). Cloned A, B, C, and D cats produced three, two, four, and five kittens after natural mating with four domestic female cats, respectively, despite later puberty of the cloned D cat than those of the other cloned male cats. Three of the 14 kittens expressed an odd eye color, which was produced by 1 and 2 from cloned A and B cats. The eye color of the other F1 kittens varied from nine brown to two blue. Body weight at birth ranged from 72.9 to 134.0 g. Although clone D had a poorer libido and entered puberty later than those of the other cloned male cats, he produced gonadal hormones within the average range. Four of the cloned male cats had normal fertility. The concentration of gonadal hormones in cloned male cats was similar to two control and donor cats. The concentration of testosterone was not significantly different among clones A, B, C, D, and control cats (5.99 +/- 5.68; 3.46 +/- 2.81; 6.41 +/- 2.17; 3.75 +/- 0.34; 4.0 +/- 3.63 ng/mL, p < 0.05). The concentrations of LH and FSH were not significantly different among the cloned cats (p < 0.05). Seven male and seven female (in total 14) kittens were produced by the natural breeding with four domestic female cats. These results indicated that cloned male cats have normal reproductive fertility and lie within the normal range of gonadal hormone production. All F1 kittens were produced by natural breeding and delivery, and are still alive and have normal growth health (27 months age).

Digit ratio (2D:4D) in Lithuania once and now: testing for sex differences, relations with eye and hair color, and a possible secular change

The second-to-fourth digit ratio (2D:4D) is a sexually dimorphic somatic trait and has been proposed as a biomarker for the organizational, i.e., permanent, effects of prenatal testosterone on the human brain. Accordingly, recent research has related 2D:4D to a variety of sex-dependent, hormonally influenced traits and phenotypes. The geographical variation in typical 2D:4D is marked and presently poorly understood. This study presents the first investigation into the 2D:4D ratio in a Baltic country. A contemporary sample of 109 Lithuanian men and women was compared with data from a historical sample of 100 Lithuanian men and women, collected and published in the 1880s and rediscovered only now. The findings included the following lines of evidence: (i) seen in an international perspective, the average 2D:4D in Lithuania is low; (ii) there was a sex difference in 2D:4D in the expected direction in both samples; (iii) a previously adduced hypothesis of an association of lighter eye and hair color with higher, i.e., more feminized, 2D:4D received no support in both samples; and (iv) the average 2D:4D in the contemporary sample was higher than in the historical sample. In view of a hypothesized increase in 2D:4D in modern populations, owing to increased environmental levels of endocrine disruptors such as xenoestrogens, this latter finding appears to be of particular notice. However, because finger-length measurement methods differed across the samples, it cannot be safely ruled out that the apparent time trend in Lithuanian 2D:4D in truth is an artifact. The puzzling geographical pattern seen in the 2D:4D ratio and the question of possible time trends therein deserve further investigations.

Multilocus OCA2 genotypes specify human iris colors

Human iris color is a quantitative, multifactorial phenotype that exhibits quasi-Mendelian inheritance. Recent studies have shown that OCA2 polymorphism underlies most of the natural variability in human iris pigmentation but to date, only a few associated polymorphisms in this gene have been described. Herein, we describe an iris color score (C) for quantifying iris melanin content in-silico and undertake a more detailed survey of the OCA2 locus (n = 271 SNPs). In 1,317 subjects, we confirmed six previously described associations and identified another 27 strongly associated with C that were not explained by continental population stratification (OR 1.5-17.9, P = 0.03 to <0.001). Haplotype analysis with respect to these 33 SNPs revealed six haplotype blocks and 11 hap-tags within these blocks. To identify genetic features for best-predicting iris color, we selected sets of SNPs by parsing P values among possible combinations and identified four discontinuous and non-overlapping sets across the LD blocks (p-Selected SNP sets). In a second, partially overlapping sample of 1,072, samples with matching diplotypes comprised of these p-Selected OCA2 SNPs exhibited a rate of C concordance of 96.3% (n = 82), which was significantly greater than that obtained from randomly selected samples (62.6%, n = 246, P<0.0001). In contrast, the rate of C concordance using diplotypes comprised of the 11 identified hap-tags was only 83.7%, and that obtained using diplotypes comprised of all 33 SNPs organized as contiguous sets along the locus (defined by the LD block structure) was only 93.3%. These results confirm that OCA2 is the major human iris color gene and suggest that using an empirical database-driven system, genotypes from a modest number of SNPs within this gene can be used to accurately predict iris melanin content from DNA.

Circulating adiponectin levels in relation to melanoma: A case–control study

AIM

Melanoma, a malignancy with steadily increasing prevalence, has been associated not only with sun exposure but also with phenotypic characteristics including obesity. Adiponectin, an adipocyte secreted endogenous insulin sensitizer, has been found to play a protective role in several obesity related cancers but has not yet been studied in relation to melanoma. We investigated the association of circulating adiponectin levels with melanoma in Greece, a country with rather low incidence of the disease and high annual sunshine levels.

METHODS

In the context of a case-control study, we studied over a 22-month period 55 patients with incident, histologically confirmed melanoma cases and 165 healthy controls matched for gender and age.

RESULTS

After controlling for the possible confounding effect of education, body mass index and waist-to-hip ratio in multiple logistic regression analyses, sun sensitive skin type was significantly and positively associated with melanoma risk (OR: 2.48, 95% Confidence Interval: 1.22-5.10, p: 0.01). On the contrary, there was a sizeable, though non-significant, inverse association of serum adiponectin levels with the disease (OR: 0.75, 95% Confidence Interval: 0.52-1.10, p: 0.14).

CONCLUSION

A protective role of adiponectin in the development of melanoma cannot be excluded given the presented empirical evidence (25% reduction per one SD of adiponectin) and the direct anti-neoplastic features of the hormone. The results are intriguing enough to point to the need for further investigation.

Influence of eye colors of Caucasians and Asians on suppression of melatonin secretion by light

This experiment tested effects of human eye pigmentation depending on the ethnicity on suppression of nocturnal melatonin secretion by light. Ten healthy Caucasian males with blue, green, or light brown irises (light-eyed Caucasians) and 11 Asian males with dark brown irises (dark-eyed Asians) volunteered to participate in the study. The mean ages of the light-eyed Caucasians and dark-eyed Asians were 26.4 ± 3.2 and 25.3 ± 5.7 years, respectively. The subjects were exposed to light (1,000 lux) for 2 h at night. The starting time of exposure was set to 2 h before the time of peak salivary melatonin concentration of each subject, which was determined in a preliminary experiment. Salivary melatonin concentration and pupil size were measured before exposure to light and during exposure to light. The percentage of suppression of melatonin secretion by light was calculated. The percentage of suppression of melatonin secretion 2 h after the start of light exposure was significantly larger in light-eyed Caucasians (88.9 ± 4.2%) than in dark-eyed Asians (73.4 ± 20.0%) ( P < 0.01). No significant difference was found between pupil sizes in light-eyed Caucasians and dark-eyed Asians. These results suggest that sensitivity of melatonin to light suppression is influenced by eye pigmentation and/or ethnicity.

The influence of social status on the rate of growth, eye color pattern and insulin-like growth factor-I gene expression in Nile tilapia, Oreochromis niloticus

Many aspects of teleost physiology are subject to regulation by social interactions. To evaluate the relationship of social status with growth, eye color pattern and hepatic Insulin-like Growth Factor-I (IGF-I) mRNA expression, 30 Oreochromis niloticus were isolated for 10 days and were used in a social pair study. Results revealed that growth of both dominant (except 1 day after social interaction) and subordinate individuals was suppressed, but growth suppression was greater in the subordinates. The dominant fish completely inhibited the feeding of the subordinate individuals during and 1 day after they were introduced into the aquaria together. After that, a pattern of highly aggressive attacks by dominant fish only partially inhibited feeding by the subordinates. Differential alterations in growth rate between dominants and subordinates were attributed more to behavioral changes (i.e., feeding) as transduced by physiological regulators (i.e., IGF-I level and possibly serotonin and/or neuropeptide Y) but may also be due to changes in metabolism. The fish's relative position in the social hierarchy consistently influenced the levels of IGF-I mRNA in the liver and the eye color pattern. Lower social status depressed hepatic IGF-I levels while dominant status stimulated hepatic IGF-I production, possibly in response to inhibition of somatostatin release in the hypothalamus, leading to greater secretion of pituitary growth hormone (GH). A significant positive association was detected between the IGF-I mRNA expression of the dominant fish and the level of aggression (number of attacks) during the encounter. Social status also influenced the eye color pattern of the fish. During aggressive interactions, most of the fish (22 out of 24) displayed decreased eye darkening. At the later part of the encounter, all subsequent subordinates displayed eye-darkening patterns which acted as a social signal announcing social submission. After the encounter dominant fish had paler eye color pattern than subordinates.

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.

Preliminary study on eye colour in Japanese macaques (Macaca fuscata) in their natural habitat

Eye colour in Japanese macaques shows apparent differences between individuals, continuously ranging from orange (bright), through shades of yellow and hazel-blue to dark blue (dark). We arbitrarily classified them into either 'yellow' eyes or 'blue' eyes based on the yellow area occupying in the iris' peripupillary ring. Most Japanese macaques have yellow eyes after infant phase, whilst 19, 17, 12, and 15% of monkeys (>6 months, sexes combined) have blue-eye in studied two groups of Shodoshima and two groups of Takasakiyama, respectively. Frequency of eye colour did not differ between males and females, but significantly differed in each age class. Blue eyes significantly more frequently occurred in newborns, infants and aged monkeys than in juveniles and prime adults. Data from mother-infant pairs indicated eye colour could be inherited from their parents. A case of asymmetric eye colour in Japanese macaques was found from a sample of 1962 individuals. Eye colour variation of Japanese macaques was discussed in relation to those of humans and rhesus macaques. A possible evolutionary model of eye colour in Japanese macaques was discussed.

Influence of age, gender and iris color on mechanical and chemical sensitivity of the cornea and conjunctiva

The purpose of this study was to establish the influence of age, gender and iris color on the mechanical and chemical sensitivity of the cornea and the conjunctiva. In 57 healthy subjects (27 males, 30 females; ages between 23 and 71 years), sensory thresholds to mechanical and chemical stimulation were measured in the central cornea and the temporal conjunctiva using a Belmonte's gas esthesiometer. Mechanical stimulation consisted of warmed air pulses of 3s duration at different flow rates (40-200 ml/min). For chemical (acidic) stimulation, 3-s warmed gas pulses containing 10% to 80% CO(2) in air were applied, at a flow below mechanical threshold flow. Corneal and conjunctival thresholds to mechanical and chemical stimuli increased with age. Premenopausal women were more sensitive to corneal stimulation than men of similar ages but overall differences in mechanical and chemical threshold between men and women were not significant. Individuals with blue eyes had significantly lower corneal chemical thresholds than those with brown or green eyes. Multiple linear regression analysis evidenced that corneal mechanical threshold depends on age and iris color according to the equation 58.2 ml/min+1.3.(Age-23 years)-9.7 if blue eyes. For chemical threshold, the equation was 28.6%CO(2)+05.(Age-23 years)-12.5 if blue eyes. In the case of the conjunctiva, only age determined mechanical and chemical thresholds according to the equations: 78.2 ml/min+1.4.(Age-23 years) and 41.6%CO(2)+0.8.(Age-23 years), respectively. Therefore, normal values of mechanical and chemical thresholds of the cornea and conjunctiva measured with the Belmonte gas esthesiometer can be predicted according to age and iris color. Variations of sensitivity with age, iris color and gender may reflect differences in innervation density and neural responsiveness associated with the hormonal status.

The relationship among race, iris color, central corneal thickness, and intraocular pressure

PURPOSE

Central corneal thickness (CCT) influences applanation intraocular pressure (IOP) measurement. The present study sought to determine whether iris color might represent a qualitative surrogate for CCT or race, and therefore differential risk for elevated IOP and, consequently, developing glaucoma.

METHODS

Eligible patients included those with best-corrected visual acuity (BCVA) better than 20/40 and who had not worn contact lenses within 24 hours. Exclusion criteria were prior ophthalmic surgery, topical ocular or systemic medication that would influence IOP, previous ocular inflammatory conditions, or current treatment for ophthalmic treatment. Data collection included demographic (name, date of birth, race), BCVA, and iris color. Iris color was judged according to a purpose-developed chart (white: blue, green, brown or black: brown) and patients were assigned to one of four groups. Goldmann applanation tonometry and pachymetry measurements were performed consecutively. To attain a power of 90% to find a difference of 40 microm with alpha < 0.05, we examined at least 14 subjects (28 eyes) for each group.

RESULTS

Comparing pachymetry measurements among iris colors revealed no statistically significant difference among the three groups of whites: blue (552 microm), green (552 microm), and brown (562 microm). The same held true when comparing IOP and CCT-adjusted IOP with iris color: blue-15.2, 15.1, green-15.4, 15.2, and brown-14.7, 14.0. When comparing CCT between whites and blacks, CCT was significantly thinner in blacks (533 microm), whether evaluating all whites (555 microm, p = 0.03) or comparing only the brown-iris white group with the black group (562 microm vs. 533 microm, p = 0.03). Mean CCT-adjusted IOP was barely significantly different between whites (14.8) and blacks (16.7) (p = 0.04).

CONCLUSION

These results suggest that iris color is not associated with CCT and apparently iris color does not influence measured IOP. We were able to establish a relationship between race and IOP when adjusting IOP for CCT. Our data show a significantly higher CCT-adjusted IOP for blacks than whites demonstrating a racial difference in CCT-corrected IOP.

Ca++-switch induction of RPE differentiation

Cultured retinal pigment epithelial (RPE) cells are commonly used as a model of the tissue to study their involvement in visual diseases. Unfortunately, cultured RPE often lose their differentiated phenotype reducing their usefulness as a model of the RPE in vivo. In this study, we used a Ca++-switch protocol to initiate the patterned expression of several phenotypic and functional markers of RPE differentiation. Cultured RPE cells from adult donors were maintained through at least six serial passages prior to assay to minimize their differentiated properties. The cells were then subjected to the Ca++-switch protocol and maintained at confluence for up to 4 months. Paired control and Ca++-switch cells were examined for phenotype, pigmentation, and the expression of tyrosinase, CRABP, myocilin, and bestrophin by western blot analysis. The Ca++-switch protocol led to a rapid restriction of N-cadherin to lateral cell borders, and to expression of tyrosinase by day 4. After 8 weeks, the experimental RPE monolayers began to accumulate visible pigment, and after 12 weeks CRABP expression was observed. Myocilin was observed at 4 months after the Ca++-switch but bestrophin was not detected at any time point. Our results suggest this protocol may drive epithelial morphogenesis in RPE cells. We note two specific differences in cells plated in low Ca++, reduced spreading on the substrate and coordinated development of cadherin adhesion when the Ca++-concentration is returned to normal. Thus, we suggest that this method produces phenotypic changes through multiple cell signalling pathways.

Canine limbal melanoma: 30 cases (1992-2004). Part 1. Signalment, clinical and histological features and pedigree analysis

OBJECTIVES

(1) To review the signalment, clinical, and histological features of canine limbal melanoma; (2) to perform pedigree analysis on breeds predisposed to limbal melanoma to establish if common ancestry exists; and (3) to investigate if any ancestral relationship exists between canine limbal melanoma and canine anterior uveal melanoma (CAUM).

DESIGN

Retrospective study.

ANIMALS STUDIED

Thirty dogs with limbal melanoma.

METHODS

Medical records of patients were reviewed. Follow-up information was obtained by re-examination of patients or telecommunications with the referring veterinary surgeons or the owners. Pedigrees were analyzed for common ancestry amongst affected dogs. RESULTS The mean age (+/- SD) at diagnosis was 6.2 (+/- 2.75) years with a range from 1 to 11 years. There was a bimodal distribution of ages with a peak at 3-4 years and a peak at 7-10 years. There was no eye predilection or predisposition for sex or coat color. Twenty-five (83%) of the limbal melanomas occurred within a dorsal arc from the dorsomedial to the ventrolateral limbus. Golden retrievers were four times more common in the melanoma group compared to the Animal Health Trust population (P < 0.0001). Labrador retrievers were three times more common in the melanoma group (P=0.01). Pedigree analysis on eight Golden retrievers [limbal melanoma (n=5), CAUM (n=2) and diffuse ocular melanosis (n=1)], revealed a pattern of inter-relatedness consistent with the condition(s) being caused, at least in part, by a genetic mutation(s). A similar level of inter relatedness was evident in six Labrador retrievers (limbal melanoma (n=2) and CAUM (n=4)). In 5/22 cases (23%), histological features suggestive of malignancy were present including intratumor necrosis in 4/22 cases (18%) and cellular atypia in 1/22 cases (5%).

CONCLUSIONS

In Golden and Labrador retrievers there is evidence that limbal melanomas, CAUM and ocular melanosis are at least in part heritable and that the same genetic mutation(s) may be causally associated with melanocytic disease at different ocular sites. The same genetic mutation(s) may be present in these two breeds. Histology should be performed on all cases to identify those with greater malignant potential.

Brainstem auditory evoked responses and ophthalmic findings in llamas and alpacas in Eastern Canada

Seventeen llamas and 23 alpacas of various coat and iris colors were evaluated for: (1) deafness by using brainstem auditory evoked response testing; and (2) for ocular abnormalities via complete ophthalmic examination. No animals were deaf. The most common ocular abnormalities noted were iris-to-iris persistent pupillary membranes and incipient cataracts.

Persistence time of loss-of-function mutations at nonessential loci affecting eye color in Drosophila melanogaster

Persistence time of a mutant allele, the expected number of generations before its elimination from the population, can be estimated as the ratio of the number of segregating mutations per individual over the mutation rate per generation. We screened two natural populations of Drosophila melanogaster for mutations causing clear-cut eye phenotypes and detected 25 mutant alleles, falling into 19 complementation groups, in 1164 haploid genomes, which implies 0.021 eye mutations/genome. The de novo haploid mutation rate for the same set of loci was estimated as 2 x 10(-4) in a 10-generation mutation-accumulation experiment. Thus, the average persistence time of all mutations causing clear-cut eye phenotypes is approximately 100 generations (95% confidence interval: 61-219). This estimate shows that the strength of selection against phenotypically drastic alleles of nonessential loci is close to that against recessive lethals. In both cases, deleterious alleles are apparently eliminated by selection against heterozygous individuals, which show no visible phenotypic differences from wild type.

Wavelength dependence of intraocular straylight

Wavelength dependence of retinal straylight has been a mystery since Stiles in 1929 [Stiles,W.S., 1929. The scattering theory of the effect of glare on the brightness difference threshold. Proc. R. Soc. Lond. (Biol.) 105, 131-41.] supposed it to have the strong Rayleigh type lambda(-4) dependence, typical for small particle light scattering, but which was never found. Using the accurate 'compensation comparison' approach, retinal straylight was measured from 625 to 457 nm. Subjects with a large variety of ocular pigmentation were included. Straylight was found to depend strongly on pigmentation of the eye, in addition to age. Young and well-pigmented eyes (young negroids) show nearly perfect lambda(-4) dependence. With less pigmentation (blue-eyed Caucasians), a red dominated component is added, negating the lambda(-4) dependence.

The Association Between Eye Color and Corneal Sensitivity Measured Using a Belmonte Esthesiometer

PURPOSE

The purpose of this study is to determine the association between corneal sensitivity measured using a pneumatic esthesiometer and eye color quantified objectively.

METHODS

Twenty subjects had ocular surface sensitivity measured using a Belmonte esthesiometer. An ascending method of limits followed by the method of constant stimuli were used to estimate 1) cold detection thresholds, 2) discomfort detection thresholds (both using pneumatic stimuli at 20 degrees C, 3) mechanical detection thresholds using pneumatic stimuli at 50 degrees C (ocular surface temperature approximately 33 degrees C), and 4) percent CO2 chemical detection thresholds using 50 degrees C pneumatic stimuli at flow rates set at half of each subject's pneumatic detection threshold (therefore detected by the chemical content and not the mechanical content). Eye color was estimated 1) clinically by two observers ranking the color (light to dark) of digital images of each subject's iris, 2) photometrically by measuring iris luminance, and 3) using chromaticity obtained from a Photo Research 650 spectroradiometer with controlled illumination. Correlation and linear and nonlinear regression analyses were used to examine relationships between variables.

RESULTS

There were no associations between eye color (determined clinically or objectively) for mechanical and chemical detection thresholds (best r = 0.15, all p > 0.05). There was a significant linear association between 20 degrees detection thresholds and eye color (r = 0.39), which was substantially improved with a two-line function (part level and part increasing linearly, r = 0.65).

CONCLUSIONS

We were generally unable to demonstrate the relationship between eye color and sensitivity reported previously using a Cochet-Bonnet esthesiometer. However, for a subset of subjects with palest irises, there appears to be a linear association between eye color and sensitivity to cooling stimuli.

Sexual selection for male dominance reduces opportunities for female mate choice in the European bitterling (Rhodeus sericeus)

Sexual selection involves two main mechanisms: intrasexual competition for mates and intersexual mate choice. We experimentally separated intrasexual (male-male interference competition) and intersexual (female choice) components of sexual selection in a freshwater fish, the European bitterling (Rhodeus sericeus). We compared the roles of multiple morphological and behavioural traits in male success in both components of sexual competition, and their relation to male reproductive success, measured as paternity of offspring. Body size was important for both female choice and male-male competition, though females also preferred males that courted more vigorously. However, dominant males often monopolized females regardless of female preference. Subordinate males were not excluded from reproduction and sired some offspring, possibly through sneaked ejaculations. Male dominance and a greater intensity of carotenoid-based red colouration in their iris were the best predictors of male reproductive success. The extent of red iris colouration and parasite load did not have significant effects on female choice, male dominance or male reproductive success. No effect of parasite load on the expression of red eye colouration was detected, though this may have been due to low parasite prevalence in males overall. In conclusion, we showed that even though larger body size was favoured in both intersexual and intrasexual selection, male-male interference competition reduced opportunities for female choice. Females, despite being choosy, had limited control over the paternity of their offspring. Our study highlights the need for reliable measures of male reproductive success in studies of sexual selection.

Zinc uptake and storage: the role of fundus pigmentation

BACKGROUND

Age-related macular degeneration (AMD) is associated with lower melanin pigmentation and is more prevalent among the elderly Caucasian population than among Africans. A correlation between light iris colour, fundus pigmentation and the incidence of AMD is reported. Moreover, melanin represents the main storage of zinc in the eye. Zinc enhances antioxidant capacity through its function as a cofactor of important enzymes or by influencing gene expression of regulatory elements in the eye. In this study, we investigated the uptake and storage of zinc in the human choroid/retinal pigment epithelium (RPE) complexes in dependence on the fundus pigmentation as judged by the iris colour.

MATERIAL AND METHODS

Choroid/RPE complexes of blue and brown human eyes were used. Tissues without any substitution served as controls. Specimens from choroid/RPE complexes were incubated with 100 microM zinc chloride for 24 h. After incubation, pieces of the complexes were stored to investigate the uptake of zinc. The rest of the tissues were kept for 3 and 7 days in culture medium (DMEM) for storage examination. The concentration of zinc was measured by inductively coupled plasma mass spectrometry.

RESULTS

After 24 h of zinc treatment the concentration of zinc in the choroid/RPE complexes of blue eyes was not significantly increased. The concentration of zinc in highly pigmented tissues (brown eyes) was increased by the factor 5.1 after 24 h and remained at high levels after 3 days (factor 4.4) and 7 days (factor 2.8).

CONCLUSIONS

Zinc uptake in the choroid/RPE complex correlates to the iris colour. Alterations of the degree of iris pigmentation result in differences of zinc uptake and storage in the choroids. A potential protective role of zinc may be more prominent in dark- than in light-coloured eyes.

Fundus pigment distribution in rhesus monkeys

There is growing evidence for an interaction among fundus pigmentation, character, geography and the function and structure of the outer retina. We examined three inbred groups of rhesus macaques (132 eyes) including all ages. One was a smaller (18 eyes) group. Coat colors were variations of brown-tan however, the smaller group had lighter 'golden' coats and colors. Fundus images were classified for pigmentation and its geographic distribution. In golden-coated animals there was bias toward nasal fundus hypopigmentation with the optic disk as a watershed demarcation zone, which extended in the superior-inferior direction. Temporal fundus hypopigmentation did not occur in the absence of nasal hypopigmentation. More common, darker coated samples showed a characteristic diffuse fundus pigmentation. There was no evidence for albinism or large variations in macular pigmentation. Rhesus monkeys can exhibit geographically controlled genetic development of fundus pigmentation. Hypopigmentation provides for access to the choroidal infrastructure.

The Pigmentation of Human Iris Influences the Uptake and Storing of Zinc

Age-related macular degeneration (AMD) is more prevalent among the elderly Caucasians than in Africans. A significant association between light iris colour, fundus pigmentation and incidence of AMD is reported, suggesting a possible correlation with melanin pigment. Zinc is known to bind to melanin in pigmented tissues and to enhance antioxidant capacity by function as a cofactor or gene expression factor of antioxidant enzymes in the eye. In this in vitro study, we investigated the uptake and storage of zinc in human irides. Irides of blue and brown human eyes were used. The number of melanocytes was measured. Tissues without any treatment served as controls. The irides were incubated with 100 microM zinc chloride in culture medium for 24 h. Specimens of the tissues were stored for the uptake examination. The remained pieces were further incubated for 3 and 7 d to investigate the storage of zinc. The concentration of zinc was measured by inductively coupled plasma mass spectrometry (ICP-MS). Melanocytes count was significantly higher in the brown tissues (P < 0.0001). Zinc concentration of blue coloured irides after 24 h zinc treatment was close to the controls. We did not observe any significant storing. In contrast, the concentration of zinc in brown irides was significantly increased after 24 h (P < or = 0.01) and remained at a high level for 7 d. The uptake of zinc is likely dependent on the amount of pigmentation in human iris. Therefore, we assume that in patients suffering from AMD the degree of pigmentation of the irides and eventually fundi should be under consideration when the patients are treated with zinc supplementation.

Latanoprost-induced pigmentation in human iridial melanocytes is fibroblast dependent

The prostaglandin F2alpha derivative, latanoprost (LT), used in glaucoma treatment, can induce pigmentation in irises of patients with hazel or heterochromatic eye colour. The mechanism by which LT induces pigmentation in the iris is not yet established, although it does not appear to induce proliferation of iridial melanocytes. The purpose of this study was to develop an in vitro model in which to investigate this mechanism. The pigmentary responses to LT and prostaglandin F(2alpha) (PGF(2alpha)) were examined in human iridial melanocytes alone or in co-culture with epithelial cells (non-ocular human epidermal keratinocytes and iris pigment epithelial cells) or mesenchymal cells (non-ocular dermal fibroblasts or iridial fibroblasts). Melanogenesis was assessed after 4 days culture with prostanoids, using dopa oxidase activity. Prostaglandin FP expression on human iridial fibroblasts and melanocytes was investigated using an immunofluorescent technique employing antibody to PGF(2alpha) receptor and RT-PCR. Iridial melanocytes did not show a convincing increase in dopa oxidase when cultured alone but in the presence of fibroblasts (ocular or non-ocular) there was a significant increase (25-30%) in dopa oxidase activity in response to 10(-7)-10(-5)m LT and PGF(2alpha). Co-culture of melanocytes with epithelial cells, while leading to increased dopa oxidase activity, did not lead to any melanogenic response to LT or PGF(2alpha). FP receptor expression was detected on fibroblasts but not iridial melanocytes by immunocytochemistry and RT-PCR. The melanocyte/fibroblast co-culture model developed in this study also showed that LT and PGF(2alpha) increased dopa oxidase activity in melanocytes from donors with brown but not blue eyes. These results suggest that LT may be inducing pigmentation in the human iris indirectly through the FP receptor on adjacent fibroblasts.

Iris colour, ethnic origin and progression of age-related macular degeneration

AIM

To investigate the relationship between iris colour, ethnic origin and the progression of age-related macular degeneration (AMD).

METHODS

Participants were recruited from the population-based Melbourne Visual Impairment Project or the prospective, randomized, double-masked Vitamin E, Cataract and Age-Related Macular Degeneration study. From these two cohorts, 171 participants aged between 52 and 93 years who were identified as having early AMD features at their baseline examination (1992-1995) were followed for an average of 6.8 years (until 2001) to determine the progression rate of early AMD. The participants' iris colour was categorized as light, intermediate or dark. Ethnic origin was categorized as Anglo-Saxon or non-Anglo-Saxon, according to the participants' grandparents' country of birth.

RESULTS

In total, 53 (31%) of the 171 participants showed signs of AMD progression. Participants with light iris colour had twofold the risk of AMD progression of those with dark or intermediate iris colours, although the age-adjusted and multivariate-adjusted associations were not significant (both P = 0.13). Age-adjusted and multivariate comparisons of Anglo-Saxon ethnic origin to non-Anglo-Saxon ethnic origin showed a noticeable but non-significant association with progression of AMD (P= 0.22 and P= 0.14, respectively).

CONCLUSION

Individuals with light iris colour or of Anglo-Saxon ethnic origin had a strong tendency to greater progression of AMD. A larger sample is required to confirm these clinically important, but statistically non-significant, associations.

Sequences Associated With Human Iris Pigmentation

To determine whether and how common polymorphisms are associated with natural distributions of iris colors, we surveyed 851 individuals of mainly European descent at 335 SNP loci in 13 pigmentation genes and 419 other SNPs distributed throughout the genome and known or thought to be informative for certain elements of population structure. We identified numerous SNPs, haplotypes, and diplotypes (diploid pairs of haplotypes) within the OCA2, MYO5A, TYRP1, AIM, DCT, and TYR genes and the CYP1A2-15q22-ter, CYP1B1-2p21, CYP2C8-10q23, CYP2C9-10q24, and MAOA-Xp11.4 regions as significantly associated with iris colors. Half of the associated SNPs were located on chromosome 15, which corresponds with results that others have previously obtained from linkage analysis. We identified 5 additional genes (ASIP, MC1R, POMC, and SILV) and one additional region (GSTT2-22q11.23) with haplotype and/or diplotypes, but not individual SNP alleles associated with iris colors. For most of the genes, multilocus gene-wise genotype sequences were more strongly associated with iris colors than were haplotypes or SNP alleles. Diplotypes for these genes explain 15% of iris color variation. Apart from representing the first comprehensive candidate gene study for variable iris pigmentation and constituting a first step toward developing a classification model for the inference of iris color from DNA, our results suggest that cryptic population structure might serve as a leverage tool for complex trait gene mapping if genomes are screened with the appropriate ancestry informative markers.

Iris color and intraocular pressure: the Blue Mountains Eye Study

PURPOSE

To assess the relationship between iris color and intraocular pressure (IOP).

DESIGN

Population-based, cross-sectional study.

METHODS

The Blue Mountains Eye Study examined 3,654 largely Caucasian participants, aged 49 to 97 years, from 1992 to 1994. Information was collected about glaucoma risk factors, and Goldmann applanation IOP measurements were taken. Iris color was assessed by comparing the undilated appearance of each eye with three standard photographs. Participants who had previous cataract or glaucoma surgery and those using glaucoma medications were excluded.

RESULTS

Mean IOP measurements increased with increasing grades of iris pigmentation. After simultaneous adjustment for variables associated with IOP, mean measurements were 15.92 mm Hg for blue iris color, 16.04 mm Hg for hazel or green, 16.11 mm Hg for tan-brown, and 16.49 mm Hg for dark brown (P for trend = .001).

CONCLUSIONS

This study demonstrates a modest but statistically significant association between increasing iris color and IOP.

Histone chaperone ASF1 cooperates with the Brahma chromatin-remodelling machinery

De novo chromatin assembly into regularly spaced nucleosomal arrays is essential for eukaryotic genome maintenance and inheritance. The Anti-Silencing Function 1 protein (ASF1) has been shown to be a histone chaperone, participating in DNA-replication-coupled nucleosome assembly. We show that mutations in the Drosophila asf1 gene derepress silencing at heterochromatin and that the ASF1 protein has a cell cycle-specific nuclear and cytoplasmic localization. Furthermore, using both genetic and biochemical methods, we demonstrate that ASF1 interacts with the Brahma (SWI/SNF) chromatin-remodelling complex. These findings suggest that ASF1 plays a crucial role in both chromatin assembly and SWI/SNF-mediated chromatin remodelling.

Colour in the eyes of insects

Many insect species have darkly coloured eyes, but distinct colours or patterns are frequently featured. A number of exemplary cases of flies and butterflies are discussed to illustrate our present knowledge of the physical basis of eye colours, their functional background, and the implications for insect colour vision. The screening pigments in the pigment cells commonly determine the eye colour. The red screening pigments of fly eyes and the dorsal eye regions of dragonflies allow stray light to photochemically restore photoconverted visual pigments. A similar role is played by yellow pigment granules inside the photoreceptor cells which function as a light-controlling pupil. Most insect eyes contain black screening pigments which prevent stray light to produce background noise in the photoreceptors. The eyes of tabanid flies are marked by strong metallic colours, due to multilayers in the corneal facet lenses. The corneal multilayers in the gold-green eyes of the deer fly Chrysops relictus reduce the lens transmission in the orange-green, thus narrowing the sensitivity spectrum of photoreceptors having a green absorbing rhodopsin. The tapetum in the eyes of butterflies probably enhances the spectral sensitivity of proximal long-wavelength photoreceptors. Pigment granules lining the rhabdom fine-tune the sensitivity spectra.

Randomized, double-masked, placebo-controlled comparison of the efficacy of emedastine difumarate 0.05% ophthalmic solution and ketotifen fumarate 0.025% ophthalmic solution in the human conjunctival allergen challenge model

BACKGROUND

Emedastine difumarate 0.05% ophthalmic solution and ketotifen fumarate 0.025% ophthalmic solution are 2 topical antiallergic agents available in the United States and other countries. Emedastine is indicated for the temporary relief of the signs and symptoms of allergic conjunctivitis. Ketotifen is indicated for the temporary relief of ocular itching caused by allergic conjunctivitis.

OBJECTIVE

The purpose of this study was to compare the efficacy of these agents in the temporary relief of ocular itching due to allergic conjunctivitis. The 2 agents were compared with each other and with placebo (artificial tears) using the conjunctival allergen challenge (CAC) model.

METHODS

This was a single-center, randomized, double-masked, placebo-controlled study. At visit 1, CAC was performed on eligible subjects to identify the dose required to elicit a positive allergic reaction. Subjects returned after 7 days for visit 2 to confirm the allergen dose. On day 14 (+/-3) of the study, enrolled subjects were randomized to 1 of 3 treatment groups: emedastine in I eye and placebo in the other, ketotifen in 1 eye and placebo in the other, or emedastine in 1 eye and ketotifen in the other. In 25 subjects, bilateral CAC was performed 5 minutes after study medication instillation. In a second group of 20 subjects, CAC was performed 15 minutes after medication instillation. Itching was graded according to a standardized 5-point scale (0 = none to 4 = severe itching) at 3, 5, and 10 minutes postchallenge. Differences in efficacy scores between treatments and versus placebo were compared using 2-sample t tests of equal variance.

RESULTS

A total of 45 patients (mean age, 41.2 years) received treatment: 16 received emedastine in 1 eye and ketotifen in the other; 14 received emedastine in 1 eye and placebo in the other; and 15 received ketotifen in 1 eye and placebo in the other. Both emedastine and ketotifen significantly inhibited itching (P < 0.05) compared with placebo at all time points after the 5- and 15-minute CAC. Mean raw scores for the active treatments were not statistically different. The mean itching efficacy scores were also not statistically different between active treatments. No adverse events were reported in this study.

CONCLUSION

The results of this study suggest that emedastine and ketotifen are not significantly different with respect to anti-itching efficacy in the CAC model of acute allergic conjunctivitis.

Cellular and hormonal regulation of pigmentation in human ocular melanocytes

The purpose of this study was to examine some of the factors that may be relevant to regulating pigmentation in the human eye, specifically whether choroidal and iridial melanocytes are sensitive to regulation by epithelial and stromal cells and alpha-melanocyte stimulating hormone (alpha-MSH). Human choroidal and iridial melanocytes were established in culture and co-cultured with epithelial cells and stromal cells derived both from skin and from eye in order to determine their influence on choroidal and iridial melanocyte dopa oxidase activity. In all cases, co-culture of melanocytes with either epithelial cells or fibroblasts led to an increase in dopa oxidase activity during 5 days of co-culture. The extent of the increase ranged from 60% (non-significant) to as much as 185% when both fibroblasts and keratinocytes were present. The optimal ratio of fibroblasts to melanocytes was 1:10 (for dermal fibroblasts) or 1:2 (for iridial fibroblasts) and 1:1 for all epithelial cells to melanocytes. Both choroidal (three out of three cultures) and iridial (two out of three cultures) melanocytes showed increases in dopa oxidase activity to alpha-MSH when cultured in Green's media but the same cells cultured in MCDB153 were unresponsive to alpha-MSH. These in vitro studies suggest that ocular melanocytes have the capacity to be influenced by adjacent epithelial and stromal cells with respect to pigmentation.

[Dependence of lipid peroxidation on pigmentation of the porcine iris]

PURPOSE

Melanin has been shown to act as antioxidant in lipid peroxidation studies. We have now investigated lipid peroxidation in dependence on stromal pigmentation in isolated porcine irises.

METHODS

The same number of lightly pigmented and heavily pigmented porcine irises (visual selection) were homogenized in buffer (50 mmol/l Na2HPO4, 50 mmol/l NaH2PO4 and 4 mmol/l sodium azide; 1:20 w/v). 500 microliters homogenate were incubated at 37 degrees C for 5, 10, 20 and 40 min in absence and presence of Fe2+ as inducer of lipid peroxidation. Lipid peroxidation was assayed by the thiobarbituric acid (TBA) test. Results are expressed as nmol of TBA reactive material produced (TBAR) per mg protein. Fe2+ concentration of the supernatant was determined spectrophotometrically with phenanthroline.

RESULTS

70 mumol/l, 180 mumol/l and 360 mumol/l Fe2+ induced lipid peroxidation. A plateau region was reached after 20 min. Lipid peroxidation differed in dependence on stromal pigmentation in porcine irises by a factor of 2.8. 180 mumol/l Fe2+ induced 1.373 +/- 0.138 nmol TBAR/mg protein in lightly pigmented irises compared to 0.491 +/- 0.125 nmol TBAR/mg protein in heavily pigmented irises after 10 min incubation (p < 0.0001, n = 4). On the other hand, the content of Fe2+ in the supernatant was the same within error.

CONCLUSIONS

There was a stronger induction of lipid peroxidation in lightly pigmented porcine irises compared to heavily pigmented porcine irises. This effect may be related to the difference in stromal melanin content and its antioxidant activity.

Unique morphology of the human eye and its adaptive meaning: comparative studies on external morphology of the primate eye

In order to clarify the morphological uniqueness of the human eye and to obtain cues to understanding its adaptive significance, we compared the external morphology of the primate eye by measuring nearly half of all extant primate species. The results clearly showed exceptional features of the human eye: (1) the exposed white sclera is void of any pigmentation, (2) humans possess the largest ratio of exposed sclera in the eye outline, and (3) the eye outline is extraordinarily elongated in the horizontal direction. The close correlation of the parameters reflecting (2) and (3) with habitat type or body size of the species examined suggested that these two features are adaptations for extending the visual field by eyeball movement, especially in the horizontal direction. Comparison of eye coloration and facial coloration around the eye suggested that the dark coloration of exposed sclera of nonhuman primates is an adaptation to camouflage the gaze direction against other individuals and/or predators, and that the white sclera of the human eye is an adaptation to enhance the gaze signal. The uniqueness of human eye morphology among primates illustrates the remarkable difference between human and other primates in the ability to communicate using gaze signals.

Lipid peroxidation in porcine irises: dependence on pigmentation

PURPOSE

Pigmentation of the iris is caused by varying amounts of melanin pigment granula in a constant number of melanocytes in the superficial stroma. Melanin has been shown to act as antioxidant. We have now investigated lipid peroxidation in dependence on stromal pigmentation in isolated porcine irises.

METHODS

The same number of lightly and heavily pigmented porcine irises (visual selection) were homogenized (1 : 20 w/v) in buffer (50 mmol/l phosphate buffer and 4 mmol/l sodium azide). 500 microl homogenate were incubated at 37 degrees C in duplicate for 5, 10, 20 and 40 min in absence and presence of Fe2+ as inducer of lipid peroxidation. The amount of lipid peroxidation was assayed by the thiobarbituric acid (TBA) test. The results are expressed as nmol of TBA reactive material (TBAR) produced/mg protein. Fe2+ concentration of the supernatant was determined spectrophotometrically with 1,10 orthophenanthroline. Concentrations of D-glucose and D -fructose in iris tissue homogenates were determined spectrophotometrically by enzymatic bioanalysis.

RESULTS

70, 180 and 360 micromol/l Fe2+ induced lipid peroxidation. A plateau region was reached after 20 min. The amount of lipid peroxidation differed in dependence on stromal pigmentation in porcine irises. The effect was most significant at 180 micromol/l Fe2+, which induced 1.373 +/- 0.138 nmol TBAR/mg protein in lightly compared to 0.491 +/- 0.125 nmol TBAR/mg protein in heavily pigmented irises after 10 min incubation (p < 0.0001, n = 4). Similar effects (factor 2-3) were also measured after 20 and 40 min incubation. On the other hand, the content of Fe2+ in the supernatant was the same within error. Sugar concentrations (D-glucose and D-fructose) did not differ significantly for the two differently pigmented iris tissues.

CONCLUSIONS

There is a stronger induction of lipid peroxidation in lightly compared to heavily pigmented porcine irises. This effect may be related to the difference in stromal melanin content and its antioxidant activity.

Factors affecting pupil size after dilatation: the Twin Eye Study

BACKGROUND/AIMS

Well dilated pupils make eye surgery easier. A classic twin study was established to examine the relative importance of genes and environment in the variance of pupil size after mydriasis, and to examine the effects of other factors such as age, iris colour, and refractive error.

METHODS

506 twin pairs, 226 monozygotic (MZ) and 280 dizygotic (DZ), aged 49-79 (mean age 62.2 years, SD 5.7) were examined. Dilated pupil size was measured using a standardised grid superimposed over digital retroillumination images taken 50-70 minutes after mydriasis using tropicamide 1% and phenylephrine 10%. Univariate maximum likelihood model fitting was used to estimate genetic and environmental variance components.

RESULTS

Dilated pupil size was more highly correlated in MZ compared with DZ twins (intraclass correlation coefficients 0.82 and 0.39 respectively). A model specifying additive genetic and unique environmental factors showed the best fit to the data, yielding a heritability of 78-80%. Individual environmental factors explained 18-19% of the variance in this population. Age only accounted for 2-3% of the variance and refractive error and iris colour did not significantly contribute to the variance.

CONCLUSIONS

Pupil size after mydriasis is largely genetically determined, with a heritability of up to 80%.

Iris color and age-related changes in lens optical density

PURPOSE

Epidemiologic evidence indicates that dark iris color increases risk of age-related cataract. No information is currently available, however, on the effects of iris color on the lens prior to cataract development. In this study, we relate iris color to lens optical density (OD) in individuals without frank cataract.

METHODS

90 subjects with blue or green irises (light color) were compared with 87 subjects having hazel, brown, or black irises (dark color). Lens OD was measured psychophysically by comparing scotopic thresholds obtained at 410 (measuring) and 550 nm (reference). Stimuli were presented in Maxwellian view.

RESULTS

The groups with light and with dark iris color did not differ significantly in smoking habits, dietary patterns, or age. Despite other similarities between the groups, lens OD was significantly (p < 0.024) higher in the group with dark irises. The higher OD of the dark iris group was due to differences in the older subjects (> 45 years, p < 0.005), rather than the younger subjects (20-45 years) who showed no differences in lens OD.

CONCLUSION

Our data indicate that iris pigmentation may be directly related to age-associated increases in lens OD.

Visual pigments, cone oil droplets and ocular media in four species of estrildid finch

A microspectrophotometric study was conducted on the retinal photoreceptors of four species of bird: cut-throat finches (Amadina fasciata), gouldian finches (Erythrura gouldiae), white-headed munias (Lonchura maja) and plum-headed finches (Neochmia modesta). Spectral characteristics of the photoreceptors in all four species were very similar. Rods contained a medium-wavelength-sensitive visual pigment with a wavelength of maximum absorbance at 502-504 nm. Four spectrally distinct types of single cone contained a visual pigment with wavelength of maximum absorbance at either 370-373 nm (ultraviolet-sensitive), 440-447 nm (short-wavelength-sensitive); 500 nm (medium-wavelength-sensitive) or 562-565 nm (long-wavelength-sensitive). Oil droplets in the ultraviolet-sensitive single cones showed no detectable absorption between 330 nm and 800 nm. Oil droplets in the short-, medium-, and long-wavelength-sensitive single cones had cut-off wavelengths at 415-423 nm, 510-520 nm and 567-575 nm, respectively. Double cones contained the visual pigment with wavelength of maximum absorbance at 562-565 nm observed in long-wavelength-sensitive single cones. Only the principal member of the double cone pair contained an oil droplet (P-type, cut-off wavelength at 414-489 nm depending on species and retinal location). Spectral transmittance of the intact ocular media of each species was measured along the optic axis. Wavelengths of 0.5 transmittance for all species were very similar (316-318 nm).

Oxidation of 3-hydroxykynurenine to produce xanthommatin for eye pigmentation: a major branch pathway of tryptophan catabolism during pupal development in the yellow fever mosquito, Aedes aegypti

This study concerns the metabolic pathways of 3-hydroxykynurenine in Aedes aegypti mosquitoes during development with emphasis on its oxidation pathway to produce xanthommatin during eye pigmentation. Oxidation of tryptophan to 3-hydroxykynurenine is the major pathway of tryptophan catabolism in Aedes aegypti, but 3-hydroxykynurenine oxidizes easily under physiological conditions, which stimulate the production of reactive oxygen species. Our data show that in Aedes aegypti, the chemically reactive 3-hydroxykynurenine is converted to the chemically stable xanthurenic acid by a transaminase-catalyzed reaction during larval development, while 3-hydroxykynurenine is transported to the compound eyes for eye pigmentation during pupal development. Our data suggest that (1) the transamination pathway of 3-hydroxykynurenine is down-regulated during the pupal development, (2) 3-hydroxykynurenine produced in other body tissues is actively transported to the compound eyes during the pupal stage, (3) the compound eye is the place where ommochromes are produced, and (4) formation of ommochromes results from nonenzymatic oxidation of 3-hydroxykynurenine in the compound eyes.

The influence of iris color on the pupillary light reflex

BACKGROUND

This study was carried out to investigate the effect of iris color on the pupillary light reflex (PLR) in normal healthy volunteers.

METHODS

Pupil perimetry was performed on 50 healthy volunteers with the Octopus 1-2-3 automated perimeter. Within the 30-deg visual field, 33 test locations were investigated four times. Stimulus parameters were Goldmann size V (1.72 degrees), intensity 1632 cd/m2, stimulus time 200 ms, background illumination 0 cd/m2, and interstimulus interval 3 s. Pupillometric parameters studied were initial pupil size, amplitude (magnitude of pupillary contraction), latency time, contraction time, pre-PLR movement, contraction velocity, and redilation velocity. Pupillometric parameters were investigated by analysis of variance by the independent variables blue and brown irides.

RESULTS

Iris color (blue vs brown) influenced statistically significantly (P < 0.05) amplitude (0.504 mm vs 0.594 mm), contraction time (401 ms vs 407 ms), contraction velocity (13.75 mm2/s vs 16.01 mm2/s), and redilation velocity (4.80 mm2/s vs 5.66 mm2/s). Iris color did not influence initial pupil size (4.78 mm vs 4.83 mm), latency time (520 mm vs 521 ms), and pre-PLR movement (0.328 mm2/s vs 0.325 mm2/s).

CONCLUSIONS

Pupillary contraction amplitude and velocity depended on iris color, whereas pupil size and latency time were independent of iris color. Therefore, iris color might be considered when, evaluating pupillary movements in pupil perimetry.