Thomas Lee Torp

Retinal oximetry in patients with ischaemic retinal diseases

The retinal oximeter is a new tool for non‐invasive measurement of retinal oxygen saturation in humans. Several studies have investigated the associations between retinal oxygen saturation and retinal diseases. In the present systematic review, we examine whether there are associations between retinal oxygen saturation and retinal ischaemic diseases. We used PubMed and Embase to search for retinal oxygen saturation and retinal ischaemic diseases. Three separate searches identified a total of 79 publications. After two levels of manual screening, 10 studies were included: six about diabetic retinopathy (DR) and four about retinal vein occlusion. No studies about retinal artery occlusion were included. In diabetes, all studies found that increases in retinal venous oxygen saturation (rvSatO2) were associated with present as well as increasing levels of DR. Four of six studies also found increased retinal arterial oxygen saturation (raSatO2) in patients with DR. In patients with central retinal vein occlusion (CRVO), all studies found that rvSatO2 was reduced, but raSatO2 remained unchanged. Branch retinal vein occlusion was not associated with changes in retinal oxygen saturation, but this was based on a single study. In conclusion, DR is associated with increased rvSatO2 and might also be related to increased raSatO2. Central retinal vein occlusion (CRVO) is correlated with increased rvSatO2 but unrelated to raSatO2. Prospective studies are needed to expand these findings. These would tell whether retinal oximetry could be a potential tool for screening or a biomarker of treatment outcome in patients with ischaemic retinal diseases.

Changes in retinal venular oxygen saturation predict activity of proliferative diabetic retinopathy 3 months after panretinal photocoagulation

Background/Aims Proliferative diabetic retinopathy (PDR) is a severe blinding condition. We investigated whether retinal metabolism, measured by retinal oximetry, may predict PDR activity after panretinal laser photocoagulation (PRP). Methods We performed a prospective, interventional, clinical study of patients with treatment-naive PDR. Wide-field fluorescein angiography (OPTOS, Optomap) and global and focal retinal oximetry (Oxymap T1) were performed at baseline (BL), and 3 months (3M) after PRP. Angiographic findings were used to divide patients according to progression or non-progression of PDR after PRP. We evaluated differences in global and focal retinal oxygen saturation between patients with and without progression of PDR after PRP treatment. Results We included 45 eyes of 37 patients (median age and duration of diabetes were 51.6 and 20 years). Eyes with progression of PDR developed a higher retinal venous oxygen saturation than eyes with non-progression at 3M (global: +5.9% (95% CI –1.5 to 12.9), focal: +5.4%, (95% CI –4.1 to 14.8)). Likewise, progression of PDR was associated with a lower arteriovenular (AV) oxygen difference between BL and 3M (global: –6.1%, (95% CI –13.4 to –1.4), focal: –4.5% (95% CI –12.1 to 3.2)). In a multiple logistic regression model, increment in global retinal venular oxygen saturation (OR 1.30 per 1%-point increment, p=0.017) and decrement in AV oxygen saturation difference (OR 0.72 per 1%-point increment, p=0.016) at 3M independently predicted progression of PDR. Conclusion Development of higher retinal venular and lower AV global oxygen saturation independently predicts progression of PDR despite standard PRP and might be a potential non-invasive marker of angiogenic disease activity.

Temporal changes in retinal vascular parameters associated with successful panretinal photocoagulation in proliferative diabetic retinopathy: A prospective clinical interventional study

Abstract Purpose We aimed to investigate changes in retinal vascular geometry over time after panretinal photocoagulation (PRP) in patients with proliferative diabetic retinopathy (PDR). Methods Thirty‐seven eyes with PDR were included. Wide‐field fluorescein angiography (Optomap, Optos PLC., Dunfermline, Scotland, UK) was used to diagnose PDR at baseline and to assess activity at follow‐up month three and six. At each time‐point, a trained grader measured retinal vessel geometry on optic disc (OD) centred images using semiautomated software (SIVA, Singapore I Vessel Assessment, National University of Singapore, Singapore) according to a standardized protocol. Results At baseline, the mean age and duration of diabetes were 52.8 and 22.3 years, and 65% were male. Mean HbA1c was 69.9 mmol/mol, and blood pressure was 155/84 mmHg. Of the 37 eyes with PDR, eight (22%) eyes had progression at month three and 13 (35%) progressed over six months. Baseline characteristics, including age, sex, duration of diabetes, HbA1c, blood pressure, vessel geometric variables and total amount of laser energy delivered did not differ by progression status. However, compared to patients with progression of PDR, patients with favourable treatment outcome had alterations in the retinal arteriolar structures from baseline to month six (calibre, 154.3 μm versus 159.5 μm, p = 0.04, tortuosity 1.12 versus 1.10, p = 0.04) and in venular structures from baseline to month three (fractal dimension 1.490 versus 1.499, p = 0.04, branching coefficient (BC) 1.32 versus 1.37, p = 0.01). Conclusion In patients with PDR, successful PRP leads to alterations in the retinal vascular structure. However, baseline retinal vascular geometry characteristics did not predict treatment outcome.

Noninvasive Retinal Markers in Diabetic Retinopathy: Advancing from Bench towards Bedside

The retinal vascular system is the only part of the human body available for direct, in vivo inspection. Noninvasive retinal markers are important to identity patients in risk of sight-threatening diabetic retinopathy. Studies have correlated structural features like retinal vascular caliber and fractals with micro- and macrovascular dysfunction in diabetes. Likewise, the retinal metabolism can be evaluated by retinal oximetry, and higher retinal venular oxygen saturation has been demonstrated in patients with diabetic retinopathy. So far, most studies have been cross-sectional, but these can only disclose associations and are not able to separate cause from effect or to establish the predictive value of retinal vascular dysfunction with respect to long-term complications. Likewise, retinal markers have not been investigated as markers of treatment outcome in patients with proliferative diabetic retinopathy and diabetic macular edema. The Department of Ophthalmology at Odense University Hospital, Denmark, has a strong tradition of studying the retinal microvasculature in diabetic retinopathy. In the present paper, we demonstrate the importance of the retinal vasculature not only as predictors of long-term microvasculopathy but also as markers of treatment outcome in sight-threatening diabetic retinopathy in well-established population-based cohorts of patients with diabetes.

Peripheral capillary non-perfusion in treatment-naïve proliferative diabetic retinopathy associates with postoperative disease activity 6 months after panretinal photocoagulation

Background/aims With the perspective to provide individualised panretinal laser photocoagulation (PRP) for proliferative diabetic retinopathy (PDR), we evaluated if retinal peripheral capillary non-perfusion (PCNP) and oximetry, as non-invasive markers of retinal metabolism and function, could predict disease activity 6 months after PRP. Methods We performed a prospective, interventional study of patients with treatment-naïve PDR. Retinal oximetry and ultra-widefield fluorescein angiography were performed at baseline (BL) and three (3M) and 6 months (6M) after PRP by a navigated laser system. At 6M follow-up, patients were divided according to disease activity: active or inactive. Results We included 33 eyes, and 69.6% were men. At BL, the median age and duration of diabetes (with IQRs) were 51.6±23.4 and 20.0±15.0 years. Haemoglobin A1c was 63.0±17.0 mmol/mol and blood pressure was 152±37/82±24 mm Hg. At BL and M6, patients with postoperative disease activity (30.3.%, n=10) had a larger area with PCNP than those with inactive PDR (BL: 51%–75% vs 26%–50%, p=0.03; 6M: 51%–75% vs 26%–50%, p=0.03). The area of PCNP did not change from BL to 6M in either group (inactive PDR: p=0.38, active PDR: p=0.87). Changes in retinal oxygen saturation were not found to be clinical relevant. Conclusion We found the area of PCNP at all timepoints to be statistically larger in patients with active PDR 6 months after PRP treatment. Therefore, the area of PCNP, at baseline, may serve as a potential predictive marker for PDR activity after treatment.

Venous loops: a benign feature of diabetic retinopathy or cause for concern?

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Changes in retinal arterial geometry in relation to activity of proliferative diabetic retinopathy 6 months after panretinal photocoagulation

Abstracts will be available online on 25 May 2017.

Predictive value of retinal venous loops in the screening for proliferative diabetic retinopathy

© 2016 Wichtig Publishing visual acuity (VA) was 53.9, 59.1, and 55.6 letters, and central retinal thickness (CRT) was 414.8, 370.4, and 430.1 μm, respectively. At 1 year, in T1, T2, and T3, the mean VA improved by 4.4, 1.9, and 4.6 letters, accompanied by a reduction in mean CRT of 57.7, 34.0, and 92.9 μm, respectively. The VA improvements in T1 were similar to T3 at 1 year but with a lower mean number of injections (T1, 3.7; T3, 4.7) and visits (T1, 6.4; T3, 8.4). In treatment-naïve patients at 1 year, VA outcomes stratified by baseline VA of <23, ≥23 to <39, ≥39 to <60, ≥60 to <74, and ≥74 letters were 11.8, 15.0, 6.2, 1.7, and -2.4 letters, with a mean of 2.3, 2.8, 3.7, 4.1, and 4.0 injections, respectively. The rate of ocular and nonocular serious adverse events reported was 0.38% and 4.86%, respectively. Conclusions: Prior Ranibizumab-treated patients showed higher VA and lower CRT at baseline versus treatment-naïve patients. VA improved over one year irrespective of previous treatment status. Ranibizumab 0.5 mg showed substantial improvements in VA in treatment-naïve patients with low baseline VA in a real-world scenario.

Retinal vascular fractal dimension as a potential marker of treatment outcome in patients with proliferative diabetic retinopathy

© 2016 Wichtig Publishing visual acuity (VA) was 53.9, 59.1, and 55.6 letters, and central retinal thickness (CRT) was 414.8, 370.4, and 430.1 μm, respectively. At 1 year, in T1, T2, and T3, the mean VA improved by 4.4, 1.9, and 4.6 letters, accompanied by a reduction in mean CRT of 57.7, 34.0, and 92.9 μm, respectively. The VA improvements in T1 were similar to T3 at 1 year but with a lower mean number of injections (T1, 3.7; T3, 4.7) and visits (T1, 6.4; T3, 8.4). In treatment-naïve patients at 1 year, VA outcomes stratified by baseline VA of <23, ≥23 to <39, ≥39 to <60, ≥60 to <74, and ≥74 letters were 11.8, 15.0, 6.2, 1.7, and -2.4 letters, with a mean of 2.3, 2.8, 3.7, 4.1, and 4.0 injections, respectively. The rate of ocular and nonocular serious adverse events reported was 0.38% and 4.86%, respectively. Conclusions: Prior Ranibizumab-treated patients showed higher VA and lower CRT at baseline versus treatment-naïve patients. VA improved over one year irrespective of previous treatment status. Ranibizumab 0.5 mg showed substantial improvements in VA in treatment-naïve patients with low baseline VA in a real-world scenario.

Graft flow unaffected by full occlusion of left anterior descending artery during coronary artery bypass grafting in a porcine model.

BACKGROUND We investigated in a porcine model whether measuring both the flow distal to an anastomosis and the graft transit time flow (TTF) gives a more accurate picture of the true blood flow in the left anterior descending artery (LAD) than graft TTF measurement alone. METHODS We performed off-pump coronary artery bypass grafting (CABG)-left internal mammary artery (LIMA) to the LAD-on 5 Yorkshire-Landrace pigs. Snares were placed both proximal and distal to the anastomosis. Flow was measured with ultrasound and TTF. This was carried out on the LIMA and at 2 locations on the LAD. Measurements were performed at the following times: baseline, during proximal snaring, after proximal snare loosening, during distal snaring, after distal snare loosening, and during both proximal and distal snaring. RESULTS During distal snaring, the TTF dropped (P = .047), and the pulsatile index (PI) increased (P = .025), while the ultrasound flow in the LAD dropped (P = .002). During proximal and distal snaring, the ultrasound flow dropped (P = .005), but the TTF value did not change significantly, compared with baseline. CONCLUSION A high flow and a low PI were seen in the graft, both proximal and distal to the anastomosis, despite a fully occluded LAD. This result suggests that graft TTF measurement alone is not sufficient when performing CABG, and measurement of flow distal to the anastomosis is also necessary to determine the true blood flow in the LAD.