Cj Pournaras

Choroidal circulation measurements by laser Doppler flux metry

Continuous real time Laser Doppler Flowmetry (LDF), has been used in humans, for the evaluation of the subfoveal choroidal circulation and the investigation of the regulatory processes of the choroidal blood flow in response to various physiological stimuli, as increases and decreases of the ocular perfusion pressure. A progressive decrease of the choroidal blood flow was observed with the aging and the progession of the age related macular degeneration. Abnormal regulation of the choroidal blood flow in patients suffering with neovascular AMD or Diabetic microangiopathy were also reported. The correlation of the subfoveal choroidal blood flow with the anatomical changes of the choroidal circulation as observed by OCT are under investigation.

Effect of anti-VEGF drugs and steroids on the inner blood-retinal barrier, after experimental BRVO in rats: preliminary results

Purpose To evaluate the effect of anti‐VEGF drugs and steroids on the inner blood‐retinal barrier (BRB) function after experimental branch retinal vein occlusion (BRVO) in rats. The integrity of the barrier is related to the expression of occludins by retinal endothelial cells.

Rhegmatogenous retinal detachment associated to vitreous hemorrhage. Role of primary vitrectomy

Purpose The incidence of retinal break formation following acute posterior vitreous detachment is variously reported as occurring in between 8% to 15% of patients, associated up to 39% of the eyes with rhegmatogenous retinal detachment.

Laser and oxygen

Purpose To evaluate the changes in the retinal oxygen partial pressure (PO2) following photocoagulation as well as the resulting effect of the laser induced improved oxygenation, on the retinal vessels hemodynamics.

How to choose the best surgical procedure

Purpose Dealing to the localization and sealing retinal breaks, the surgical success rate for the cure of rhegmatogenous retinal detachment greatly changed with the introduction of scleral buckling (SB), intraocular gas injection, and pars plana vitrectomy (PPV).

Retinal photocoagulation and oxygenation

Purpose The clinical role of photocoagulation for the treatment of hypoxia related complications of retinal ischemic microangiopathies is well established. Methods Measurements of the partial pressure of oxygen (PO2) distribution within the the retina in various animal species using oxygen sensitive microelectrodes and evaluation of the retinal vessels reactivity by laser doppler velocimetry gave additional insights concerning photocoagulation mechanisms. Results The PO2 within the vitreo-retinal interface is heterogeneous. Preretinal and trans-retinal PO2 profiles indicate that the preretinal PO2 far away from vessels remain constant in all retinal areas. Intervascular intraretinal PO2 gradually decreases from both the vitreo-retinal interface and the choroid towards the mid-retina. Close to the pigment epithelium, it is significantly higher than at the vitreoretinal interface due to the much higher O2 supply provided by choroidal compaires to retinal circulation. Laser photocoagulation reduces the outer retina O2 consumption and allows O2 diffusion into the inner retina from the choroid raising the PO2 in the inner healthy retinal layers and in the preretinal intervascular normal areas. In this way laser treatment relieves retinal hypoxia in experimental branch vein occlusion (BRVO). In patients with diabetic retinopathy (DR), the retinal PO2 is higher in areas previously treated with laser. Following photocoagulation, the resulting reversal of hypoxia, the retinal vasculature constriction and the improvement of the regulatory response to hyperoxia all affect favorably both the retinal neovascularisation and macular edema. Conclusion Photocoagulation induces an increase of the inner retinal oxygenation reversing the retinal hypoxia and improving the regulatory response of the retinal vessels

The effect of laser on retinal oxygenation (animal studies)

Purpose: To discuss the effect of laser on the retinal oxygen distribution, in experimental animal models. Methods: Transretinal and preretinal O2 measurments were obtained by O2 sensitive micro-electrodes in anesthetized animal models. The effect of laser photogoagulation on the oxygen preretinal and transretinal distribution and retinal oxygen consumption, within normal and post experimental ischemic micro-angiopathies retinas, were calculated. Results: Laser photocoagulation, resulting to pigment epithelium and photoreceptors layers disruption, reduces the outer retina’s demand for O2 and nutrients. Transretinal PO2 measurements confirm changes of the tranretinal PO2 grandients distribution. O2 diffusing from the choroid, non consumpted by the outer retinal layers reaches the inner retina, resulting to PO2 raise in preretinal areas and in the inner healthy retinal layers of experimental animal and relieve retinal hypoxia in experimental BRVO in mini-pigs and cats. Improvement of inner retinal oxygenation affect the retinal circulation resulting to retinal vessels constriction and restoration of retinal blood flow regulation. Conclusions: Laser photocoagulation improves the inner retinal layers oxygenation thus reversing tissue hypoxia and improving the retinal blood flow regulation in retinas with ischemic micro-angiopathies. Reversal of retinal tissue hypoxia and restoration of retinal blood flow regulation potentially affect the evolution of the macular edema related to ischemic microagiopathies.