Evaluation of choroidal thickness in light-coloured eyes

Objective: The aim of this study was to determine whether iris colour is related to the choroidal thickness of healthy individuals. Methods: Healthy participants were divided into two groups. Group 1 had light-coloured eyes (blue and green), and group 2 had dark-coloured eyes (brown). The main outcome measures were iris thickness, subfoveal choroidal thickness and nasal and temporal choroidal thicknesses 500 µm away from the fovea. Results: Group 1 comprised 31 subjects with light-coloured eyes, and group 2 had 31 subjects with dark eyes. The mean ages of groups 1 and 2 were 26.7 ± 7.5 years and 24.1 ± 5.8 years, respectively ( p = 0.14). The choroidal thicknesses of the subfoveal, nasal and temporal regions were 336.3 ± 52.1 µm, 321.9 ± 43.6 µm and 318.4 ± 49.2 µm, respectively, in group 1 and 396.5 ± 76.9 µm, 372 ± 79.3 µm and 379.6 ± 82.4 µm, respectively, in group 2. All the values in group 1 were statistically lower than those in group 2 ( p = 0.001, p = 0.001 and p = 0.003, respectively). The iris thickness in group 1 (493.73 ± 95.44 µm) was thinner than in group 2 (524.61 ± 69.74 µm) but not statistically significant ( p = 0.141). Conclusion: The results showed that a thinner choroid can be seen in disease-free light-coloured eyes. The iris colour should be considered among the factors affecting the choroidal thickness, such as age, sex, race and refractive error.

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.

Age-dependent differences in iris colouration of passerines during autumn migration in Central Europe

Avian eye colour changes with age, but many aspects of this transition are still insufficiently understood. We examined if an individual’s sex, age, species and body condition are related to the iris colour in common migratory passerines during their autumn passage through Central Europe. A total of 1,399 individuals from nine numerous species were ringed and examined in late autumn in northern Poland. Each individual was sexed by plumage (if possible) and assigned to one of three classes of the iris colour—typical for immatures, typical for adults and intermediate. We found that the iris was typical in 97.7% cases of immatures and in 75.8% cases of adults and this difference was significant. Species, sex and body mass index (BMI) had no significant influence on the iris colour. We show that iris colour in passerines in late autumn is strongly age-dependent and thus can serve as a reliable feature for ageing in field studies, especially in species difficult to age by plumage.

Heterochromia irides and mistaken identity of retinoblastoma

Retinoblastoma is the most common intraocular malignancy of infancy which frequently manifests with a white pupillary reflex. We report a case of delayed presentation of a child with retinoblastoma in his left eye because parents thought the change in iris colour in this eye was due to the innocent heterochromia irides that was previously diagnosed in his elder sibling. This late presentation necessitated enucleation of the affected eye followed by chemotherapy.

Iris colour and astigmatism among Chinese teenagers

Background/aimsIris 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.Methods2346 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.ResultsThe 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).ConclusionDarker iris colour might be a risk factor for astigmatism in Chinese adolescents.

Lack of tumour pigmentation in conjunctival melanoma is associated with light iris colour and worse prognosis

AimTo investigate whether differences in iris colour, skin colour and tumour pigmentation are related to clinical outcome in conjunctival melanoma.MethodsData of 70 patients with conjunctival melanoma from the Leiden University Medical Center (Leiden, The Netherlands) and 374 patients from the Wills Eye Hospital (Philadephia, USA) were reviewed. The relation between iris colour, skin colour and tumour pigmentation versus clinical parameters and outcome was investigated using univariate and multivariate regression analyses.Results A light iris colour (blue, grey, green) was present in 261 (59%) patients and a dark colour (hazel, brown) in 183 (41%). A low tumour pigmentation was detected in 130 (40%) and a high pigmentation in 197 (60%) patients. Low tumour pigmentation was associated with light iris colour (p=0.021) but not related to skin colour (p=0.92). In univariate analysis, neither iris nor skin colour was related to clinical outcome, while a low tumour pigmentation was related to metastasis formation (HR 2.37, p=0.004) and death (HR 2.42, p=0.020). In multivariate analysis, low tumour pigmentation was related to the development of recurrences (HR 1.63, p=0.043), metastasis formation (HR 2.48, p=0.004) and death (HR 2.60, p=0.014).Conclusion Lightly pigmented tumours occurred especially in individuals with lightly coloured irises. While iris colour or skin colour was not significantly related to clinical outcome, a low tumour pigmentation was related to a worse outcome in patients with conjunctival melanoma. The amount and type of melanin in conjunctival melanocytes may be involved in the pathogenesis and behaviour of selected conjunctival melanoma.