The application of arterio-venous ratio (AVR) cut-off values in clinic to stratify cardiovascular risk in patients.

INTRODUCTION: Cardiovascular risk calculators are a useful tool for identifying at-risk individuals. There are standardised methods for assessing the retinal microcirculation which alters as a consequence of cardiovascular disease (CVD). This study aimed to explore if a standardised retinal vessel assessment conducted in primary optometric care reflects current cardiovascular risk, as measured using two validated CVD risk calculators (QRISK 2; Mayo Clinic). METHODS: A total of 120 subjects were included in the analyses. Following a routine eye examination, participants had disc-centred retinal photographs and systemic blood pressure taken. Retinal vessel parameters (central retinal artery and vein equivalent and arterio-venous ratio (AVR)) were calculated using semi-automated software. Participants were then grouped into AVR quintiles as defined by the Atherosclerosis Risk in Communities Study (ARIC). Cardiovascular risk was calculated with the validated QRISK and Mayo Clinic health calculators. RESULTS: Systolic blood pressure was significantly greater in those with an AVR value falling in the lowest quintile compared to the highest quintile (150.65 mmHg vs. 132.21 mmHg [p = 0.001]). Similarly, CVD risk was significantly higher in those with the lowest AVR compared to the highest (QRISK: 14.28% vs. 9.87% [p = 0.05]; MAYO risk: 36.35% vs. 19.21% [p = 0.01]). Chi squared analyses showed a significant difference in the number of hypertensives in the lowest AVR quintile compared to those in the highest [p = 0.02]. CONCLUSION: Whilst the ARIC population is not directly comparable to the population used to develop the QRISK calculator, it has been shown that its application could help to identify at risk individuals using retinal vessel analyses.

Comparison between two fast threshold strategies: SPARK and SITA in normal subjects.

BACKGROUND: Numerous fast threshold strategies have been developed in perimetry which use maximum likelihood approaches to estimate the threshold. A recent approach to threshold estimation has been developed estimating the threshold from a limited number of test points which further reduces examination time. This strategy, SPARK, has not been compared to the SITA strategy. The aim of this study was to compare SPARK with SITA in a normal cohort to evaluate within and between strategy agreement in threshold estimates. METHODS: A total of 83 normal subjects each underwent two visual field examinations with SITA and SPARK on two separate occasions on a randomly selected eye. The eye examined and the order of strategy examined first was randomised but remained constant over the two perimetry visits. RESULTS: Visual field examination with SPARK Precision was on average 33% faster than SITA Standard. A positive correlation between group mean sensitivities of SITA Standard and SPARK Precision (rho = 0.713, p < 0.001) was found. In total, 95% of stimulus locations were located within the 95% limits of agreement and linear regression on the differences in sensitivities showed no statistically significant proportional bias (t = 1.713, p = 0.09). Pointwise analysis showed SITA Standard had significantly larger variability for individual stimulus locations examined over two visits when compared to SPARK (t = 9.175, p < 0.001). CONCLUSION: The clinical examination of SPARK yields a sensitivity profile similar to SITA but in a faster examination time. The lower threshold variability of SPARK may be as a result of data smoothing in the threshold estimation process.

The impact of flash intensity on retinal vessel oxygen saturation measurements using dual wavelength oximetry.

PURPOSE: To establish the optimal flash settings for retinal vessel oxygen saturation parameters using dual-wavelength imaging in a multiethnic group. METHODS: Twelve healthy young subjects (mean age 32 years [SD 7]; three Mediterranean, two South Asian, and seven Caucasian individuals) underwent retinal vessel oxygen saturation measurements using dual-wavelength oximetry, noncontact tonometry, and manual sphygmomanometry. In order to evaluate the impact of flash intensity, we obtained three images (fundus camera angle 30°, ONH centered) per flash setting. Flash settings of the fundus camera were increased in steps of 2 (initial setting of 6 and the final of 22), which reflect logarithmic increasing intensities from 13.5 to 214 Watt seconds (Ws). RESULTS: Flash settings below 27 Ws were too low to obtain saturation measurements, whereas flash settings of more than 214 Ws resulted in overexposed images. Retinal arteriolar and venular oxygen saturation was comparable at flash settings of 27 to 76 Ws (arterioles' range: 85%-92%; venules' range: 45%-53%). Higher flash settings lead to increased saturation measurements in both retinal arterioles (up to 110%) and venules (up to 92%), with a more pronounced increase in venules. CONCLUSIONS: Flash intensity has a significant impact on retinal vessel oxygen saturation measurements using dual-wavelength retinal oximetry. High flash intensities lead to supranormal oxygen saturation measurements with a magnified effect in retinal venules compared with arteries. In addition to even retinal illumination, the correct flash setting is of paramount importance for clinical acquisition of images in retinal oximetry. We recommend flash settings between 27 to 76 Ws.

Statistical modelling of the central 10-degree visual field in short-wavelength automated perimetry.

BACKGROUND: Reports of short-wavelength pathway dysfunction in retinal eye disease suggest that short-wavelength automated perimetry may be a useful technique for the investigation of central visual function. The aim of this study was to adapt existing statistical procedures used for the investigation of 30-2 short-wavelength automated perimetry to the 10-2 program of the Humphrey Field Analyser. METHODS: A four- or six-point linear interpolation procedure was used to calculate normal visual field sensitivity for each of the 68 stimulus locations of the 10-2 program using empirical normal data from 51 normal subjects examined using the 30-2 program. Prediction limits for normality were derived at each stimulus location, enabling the calculation of age-corrected global perimetric indices and construction of probability maps for diffuse and focal visual field loss. The normal database was validated by empirical data from five normal subjects, stratified for age. RESULTS: The pointwise distribution of normal sensitivity exhibited a Gaussian distribution at the majority of stimulus locations. The pointwise coefficient of variation did not vary significantly across the visual field. Examples of diabetic pseudophakic patients and a patient with age-related macular degeneration are presented to illustrate the effectiveness of SWAP at detecting visual field abnormality in the central visual field. CONCLUSION: Ten-degree SWAP is able to effectively detect focal visual field loss in central retinal eye disease which may precede those found using conventional perimetry. SWAP may prove to be an invaluable technique for the investigation of central retinal eye disease.