Effect of varying skin surface electrode position on electroretinogram responses recorded using a handheld stimulating and recording system.

PURPOSE: A handheld device (the RETeval system, LKC Technologies) aims to increase the ease of electroretinogram (ERG) recording by using specially designed skin electrodes, rather than corneal electrodes. We explored effects of electrode position on response parameters recorded using this device. METHODS: Healthy adult twins were recruited from the TwinsUK cohort and underwent recording of light-adapted flicker ERGs (corresponding to international standard stimuli). In Group 1, skin electrodes were placed in a "comfortable" position, which was up to 20 mm below the lid margin. For subsequent participants (Group 2), the electrode was positioned 2 mm from the lid margin as recommended by the manufacturer. Amplitudes and peak times (averaged from both eyes) were compared between groups after age-matching and inclusion of only one twin per pair. Light-adapted flicker and flash ERGs were recorded for an additional 10 healthy subjects in two consecutive recording sessions: in the test eye, electrode position was varied from 2 to 10-20 mm below the lid margin between sessions; in the fellow (control) eye, the electrode was 2 mm below the lid margin throughout. Amplitudes and peak times (test eye normalised to control eye) were compared for the two sessions. RESULTS: Including one twin per pair, and age-matching yielded 28 individuals per group. Flicker ERG amplitudes were significantly lower for Group 1 than Group 2 participants (p = 0.0024). However, mean peak times did not differ between groups (p = 0.54). For the subjects in whom electrode position was changed between recording sessions, flash and flicker amplitudes were significantly lower when positioned further from the lid margin (p < 0.005), but peak times were similar (p > 0.5). CONCLUSIONS: Moving the skin electrodes further from the lid margin significantly reduces response amplitudes, highlighting the importance of consistent electrode positioning. However, this does not significantly affect peak times. Thus, it may be feasible to adopt a more comfortable position in participants who cannot tolerate the recommended position if analysis is restricted to peak time parameters.

Do twins share the same dress code? Quantifying relative genetic and environmental contributions to subjective perceptions of "the dress" in a classical twin study.

The phenomenon of contrasting color perceptions of "the dress" photograph has gained scientific interest. The mechanism underlying why individuals differ is yet to be fully explained. We use the powerful twin model design to ascertain the relative contribution of genetic and environmental factors on perception variation. A sample of 466 twins from the British TwinsUK registry were invited to report what color they saw in a standard image of the dress in standard illumination. The mean age of the participants was 49.5 (SD = 17.8) years, and 85% were female. When asked to choose between white and gold (WG) or blue and black (BB), 328 reported WG (70.4%) and 135 (29.0%) reported BB. Subjects choosing WG were significantly older (p < 0.01), but there was no significant difference in gender. Monozygotic (MZ) twins were more concordant in their responses than dizygotic (DZ) twins (0.46 vs. 0.36). Twin modeling revealed that genetic factors accounted for 34% (95% confidence interval, 5%-59%) of variation in the reported color of the dress when adjusted for age, whereas environmental factors contributed 66% (95% CI, 41%-95%). This study suggests environmental factors play a significant role in how an individual perceives the color of "the dress."

Cascade screening for glaucoma in high-risk family members of African-Caribbean glaucoma patients in an urban population in London.

BACKGROUND/AIMS: Cascade screening has been used successfully in relatives of patients with inherited cancers and other genetic diseases to identify presymptomatic disease. This study was designed to examine if this approach would be successful in a high-risk group: first-degree relatives (FDR) of African-Caribbean glaucoma patients resident in London. METHODS: African-Caribbean patients (probands) with glaucoma from an inner London hospital setting in a deprived area were asked to disseminate personalised information to their FDR over the age of 30 and to arrange a free hospital-based screening. Data collected, including optical coherence tomography imaging, were reviewed by a glaucoma specialist and if glaucoma was diagnosed or suspected, local specialist referral via family doctor was made. RESULTS: 203 probands were recruited from glaucoma clinics. 248 suitable FDR were identified as potentially eligible to attend screening. 57 (23%) FDR made contact with the research team of whom 18 (7%) attended a subsequent screening visit. No patients were diagnosed with glaucoma; one participant was diagnosed as glaucoma suspect. Reasons for poor uptake included reluctance by probands to involve their family members, and retirees spending significant time abroad. CONCLUSION: Cascade screening of FDR of African-Caribbean glaucoma patients in inner city London was unsuccessful. Research confidentiality guidance prohibiting research teams directly contacting family members was a barrier. Greater community engagement, community-based screening and permission to contact FDR directly might have improved uptake.

Genetic and Environmental Factors Associated With the Ganglion Cell Complex in a Healthy Aging British Cohort.

IMPORTANCE: Measurement of ganglion cell complex (GCC) thickness may be more sensitive than current methods for glaucoma diagnosis and research. However, little is known about the factors influencing GCC thickness in the general population. OBJECTIVES: To investigate the heritability of and factors associated with GCC thickness in a healthy aging population. DESIGN, SETTING, AND PARTICIPANTS: A cross-sectional twin study was conducted from August 27, 2014, to March 31, 2016, among 1657 participants of white British ancestry from the TwinsUK study cohort without ocular pathologic conditions. Heritability analyses were conducted in 1432 twins (426 monozygous and 290 dizygous pairs). Association analyses were performed using univariable and multivariable stepwise linear regression models, taking family structure into account. Heritability analyses were conducted using maximum likelihood structural equation twin modeling. MAIN OUTCOMES AND MEASURES: Parameters measured included GCC thickness, autorefraction, intraocular pressure, blood pressure, body mass index, and cholesterol, creatinine, glucose, insulin, triglycerides, and urea levels. Estimated glomerular filtration rate was calculated using the Modification of Diet in Renal Disease formula. RESULTS: Among the 1657 participants (mean [SD] age, 56.0 [15.3] years; 89.5% women and 10.5% men), the mean [SD] inner GCC thickness was 96.0 [7.6] µm (95% CI, 95.1-96.2). In multivariable modeling, the mean inner GCC thickness was associated with advancing age (ß, -0.14; P < .001), increased body mass index (ß, -0.15; P = .001), spherical equivalent (ß, 0.70; P < .001), and higher estimated glomerular filtration rate (ß, 0.03; P = .02). A 1-U increase in age or body mass index was associated with a 0.14-µm and 0.15-µm decrease in GCC thickness, respectively (P < .001), while a 1-U increase in spherical equivalent or estimated glomerular filtration rate was associated with a 0.70-µm (P < .001) and 0.03-µm (P = .02) increase in GCC thickness, respectively. Ganglion cell complex thickness was not associated with sex, intraocular pressure, or diabetes. Age-adjusted GCC thickness was highly heritable, with additive genetic effects explaining 81% (95% CI, 78%-84%) of phenotypic variance and individual environmental factors explaining the remaining 19% (95% CI, 16%-22%). CONCLUSIONS AND RELEVANCE: Ganglion cell complex thickness appears to be highly heritable and further genetic analysis may help identify new biological pathways for glaucoma. The results suggest it may be important to account for age, body mass index, refractive error, and sex when using GCC thickness as a diagnostic tool. Replication of their results is required, as is further research to explain the association between renal function and GCC thickness.

Clinical Characteristics of Dry Eye Patients With Chronic Pain Syndromes.

PURPOSE: To investigate clinical characteristics of dry eye disease (DED) patients with a chronic pain syndrome. DESIGN: Cross-sectional study. METHODS: Four hundred twenty-five patients of a tertiary care DED patient cohort in the Netherlands were included. Chronic pain syndromes irritable bowel syndrome, chronic pelvic pain, and fibromyalgia were assessed by questionnaires. Outcome variables were the Ocular Surface Disease Index (OSDI) symptom questionnaire, tear osmolarity, Schirmer test, tear breakup time, conjunctival hyperemia, staining of the cornea and conjunctiva, and amount of mucus. Outcomes were cross-sectionally compared between DED patients with a chronic pain syndrome and those without. RESULTS: A total of 74 out of 425 DED patients (17%) had at least 1 chronic pain syndrome. The total symptom score was significantly higher in DED patients with a chronic pain syndrome than in those without (45.8 vs 33.8, P < .0005). Moreover, patients with a chronic pain syndrome scored higher on every single subscale of the 12-item OSDI symptom questionnaire. However, ocular signs were similar or even less severe in these patients. Similarly, in 64 DED patients from the population-based cohort TwinsUK, patients with a chronic pain syndrome (n = 24, 38%) had higher subscale and total (34.1 vs 14.4, P = .001) symptom scores. CONCLUSION: In DED patients, chronic pain syndromes are common and are associated with increased severity of DED symptoms across all domains of the OSDI, even though objective ocular surface signs are no worse. In clinical practice, more awareness of chronic pain syndromes might help in understanding the discrepancy between signs and symptoms in DED.

Prevalence and risk factors of dry eye disease in a British female cohort.

BACKGROUND/AIMS: To estimate the prevalence and risk factors of dry eye disease (DED) in a female cohort in the UK. METHODS: Population-based cross-sectional association study of 3824 women from the TwinsUK cohort aged 20-87 years. A questionnaire was used to evaluate DED and several risk factors. Binary logistic regression, corrected for age, was used to examine the association between DED and risk factors. RESULTS: 9.6% of women had a DED diagnosis and concomitant use of artificial tears, and 20.8% experienced DED symptoms in the past 3 months. Risk factors that were significantly associated with DED were age, asthma, eczema, the presence of any allergy, cataract surgery, rheumatoid arthritis, osteoarthritis, migraine and stroke. The highest effect sizes were found with depression, pelvic pain, irritable bowel syndrome and chronic widespread pain syndrome (all p<0.0005). Subjects with DED symptoms scored significantly lower on self-perceived health, compared with controls (p=0.001). CONCLUSIONS: DED is common and increases with age within this cohort of female twins. We confirmed established risk factors for the first time in a British population, and found important risk factors that might relate to an underlying aetiology involving chronic pain predisposition or somatisation.

The heritability of dry eye disease in a female twin cohort.

PURPOSE: We estimated the relative importance of genes and environment in dry eye disease (DED) using a classic twin study. METHODS: A large sample of 3930 female monozygotic and dizygotic twins from the UK Adult Twin Registry (TwinsUK) was questioned about the presence of a DED diagnosis and about DED symptoms in the preceding 3 months. In addition, a subset of 606 twins was examined for several dry eye signs. Genetic and environmental effects were estimated using maximum likelihood structural equation modeling. RESULTS: All DED outcome variables showed higher correlation in monozygotic twin pairs than in dizygotic twin pairs, suggesting genes have a contributory role in DED. The DED symptoms showed a heritability of 29% (95% confidence interval [CI], 18%-40%). A clinician's diagnosis of DED with concurrent use of artificial tears showed a heritability of 41% (95% CI, 26%-56%). Estimates of the heritability of DED signs were 25% (95% CI, 7%-42%) for interblink interval, 58% (95% CI, 43%-70%) for Schirmer value, 40% (95% CI, 25%-53%) for tear osmolarity, and 78% (95% CI, 59%-90%) for the presence of blepharitis. The unique environment explained the remainder of the variance. We found no significant heritability for tear breakup time. CONCLUSIONS: Genetic factors contribute moderately to the diagnosis, symptoms, and the signs of DED. Compared to other ocular phenotypes, the lower heritability might reflect some of the difficulties in objective phenotyping of DED in a population-based sample. However, future genetic studies are now justified and may help in unraveling the pathophysiology of DED.

Relationship between dry eye symptoms and pain sensitivity.

IMPORTANCE: Dry eye disease (DED) is common, but little is known about factors contributing to symptoms of dry eye, given the poor correlation between these symptoms and objective signs at the ocular surface. OBJECTIVE: To explore whether pain sensitivity plays a role in patients' experience of DED symptoms. DESIGN, SETTING, AND PARTICIPANTS: A population-based cross-sectional study of 1635 female twin volunteers, aged 20 to 83 years, from the TwinsUK adult registry. MAIN OUTCOMES AND MEASURES: Dry eye disease was diagnosed if participants had at least 1 of the following: (1) a diagnosis of DED by a clinician, (2) the prescription of artificial tears, and/or (3) symptoms of dry eyes for at least 3 months. A subset of 689 women completed the Ocular Surface Disease Index (OSDI) questionnaire. Quantitative sensory testing using heat stimulus on the forearm was used to assess pain sensitivity (heat pain threshold [HPT]) and pain tolerance (heat pain suprathreshold [HPST]). RESULTS: Of the 1622 participants included, 438 (27.0%) were categorized as having DED. Women with DED showed a significantly lower HPT (P = .03) and HPST (P = .003)--and hence had higher pain sensitivity--than those without DED. A strong significant association between the presence of pain symptoms on the OSDI and the HPT and HPST was found (P = .008 for the HPT and P = .003 for the HPST). In addition, participants with an HPT below the median had DED pain symptoms almost twice as often as those with an HPT above the median (31.2% vs 20.5%; odds ratio, 1.76; 95% CI, 1.15-2.71; P = .01). CONCLUSIONS AND RELEVANCE: High pain sensitivity and low pain tolerance are associated with symptoms of DED, adding to previous associations of the severity of tear insufficiency, cell damage, and psychological factors. Management of DED symptoms is complex, and physicians need to consider the holistic picture, rather than simply treating ocular signs.