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1.  Value of retinal vein pulsation characteristics in predicting increased optic disc excavation 
Retinal vein pulsation is often absent in glaucoma, but can be induced by applying a graded ophthalmodynamometric force (ODF) to the eye, which is elevated in glaucoma.
To assess whether ODF has a predictive value in determining glaucoma progression.
75 patients with glaucoma and suspected glaucoma were examined prospectively in 1996, and then re‐examined at a mean of 82 months later. All subjects had intraocular pressure, visual fields, stereo optic disc photography and ODF measured on their initial visit. When venous pulsation was spontaneous, the ODF was said to be 0 g. At re‐examination, central corneal thickness and blood pressure were also measured. Initial and subsequent optic disc photographs were compared and graded into those that had increased excavation and those that had remained stable. The relationship between increased excavation (recorded as a binary response) and the measured variables was modelled using a multiple mixed effects logistic regression.
ODF at the initial visit was strongly predictive of increased excavation (p = 0.004, odds ratio 1.16/g, range 0–60 g), with greater predictive value in women than in men (p = 0.004). Visual field mean deviation was predictive of increased excavation (p = 0.044), as was optic nerve haemorrhage in association with older age (p = 0.038). Central corneal thickness was not significantly predictive of increased excavation (p = 0.074) after having adjusted for other variables.
ODF measurement seems to be strongly predictive of the patient's risk for increased optic disc excavation. This suggests that ODF measurement may have predictive value in assessing the likelihood of glaucoma progression.
PMCID: PMC1994760  PMID: 17035270
2.  Objective Detection of Retinal Vessel Pulsation 
PLoS ONE  2015;10(2):e0116475.
Retinal venous pulsation detection is a subjective sign, which varies in elevated intracranial pressure, venous obstruction and glaucoma. To date no method can objectively measure and identify pulsating regions.
Using high resolution video-recordings of the optic disk and retina we measured fluctuating light absorption by haemoglobin during pulsation. Pulsation amplitude was calculated from all regions of the retinal image video-frames in a raster pattern. Segmented retinal images were formed by objectively selecting regions with amplitudes above a range of threshold values. These were compared to two observers manually drawing an outline of the pulsating areas while viewing video-clips in order to generate receiver operator characteristics.
216,515 image segments were analysed from 26 eyes in 18 research participants. Using data from each eye, the median area under the receiver operator curve (AU-ROC) was 0.95. With all data analysed together the AU-ROC was 0.89. We defined the ideal threshold amplitude for detection of any pulsating segment being that with maximal sensitivity and specificity. This was 5 units (95% confidence interval 4.3 to 6.0) compared to 12 units before any regions were missed. A multivariate model demonstrated that ideal threshold amplitude increased with increased variation in video-sequence illumination (p = 0.0119), but between the two observers (p = 0.0919) or other variables.
This technique demonstrates accurate identification of retinal vessel pulsating regions with no areas identified manually being missed with the objective technique. The amplitude values are derived objectively and may be a significant advance upon subjective ophthalmodynamometric threshold techniques.
PMCID: PMC4314073  PMID: 25643350
3.  An experimental study of VEGF induced changes in vasoactivity in pig retinal arterioles and the influence of an anti-VEGF agent 
BMC Ophthalmology  2012;12:10.
Vascular endothelial growth factor (VEGF) plays an important role in ocular physiology. Anti-VEGF agents are now used for treatment of common retinal diseases. This study characterises the vasoactive properties of VEGF in isolated perfused pig retinal arterioles under normal tone or endothelin-1 (ET-1) pre-contracted conditions and determines the influence of an anti VEGF agent on VEGF induced vasoactivity.
An isolated perfused retinal arteriole preparation was used. The outer diameter of retinal vessels was monitored at 2 second intervals in response to VEGF and the anti VEGF agent, bevacizumab. The effect of intraluminal delivery of VEGF was determined over a wide concentration range (10-16 to 10-7 M) both with and without pre-contraction with ET-1 (3 x 10-9 M). Bevacizumab (0.35 mg mL-1) was applied extraluminally to determine the influence of bevacizumab on VEGF induced vasoactive changes on ET-1 pre-contracted vessels.
In retinal arterioles with normal tone, VEGF induced a concentration dependent contraction at low concentrations, reaching 93.5% at 10-11 M and then contraction was reduced at higher concentrations, recovering to 98.1% at 10-7 M. VEGF produced a potent concentration dependent vasodilatation in arterioles pre-contracted with ET-1. VEGF induced vasodilatation in arterioles pre-contracted with ET-1 was significantly inhibited by bevacizumab.
VEGF induced vasoactive changes in pig retinal arterioles are dependent on concentration and vascular tone. Bevacizumab inhibits VEGF-induced vasodilatation in pre-contracted arterioles.
PMCID: PMC3395563  PMID: 22642643

Results 1-3 (3)