Anatomical and Functional Results of Lamellar Macular Holes Surgery.

PURPOSE: To determine the long-term surgical findings and outcomes after vitrectomy for symptomatic lamellar macular holes. METHODS: We studied 28 patients with lamellar macular holes and central visual loss or distortion. All interventions were standard 25 G vitrectomy with membranectomy of the internal limiting membrane (ILM), peeling and gas tamponade with SF6 20 %. Operations were performed by a single experienced surgeon within the last 3 years. Best corrected visual acuity and optical coherence tomography appearance were determined preoperatively and postoperatively. RESULTS: Following the surgical procedure, all macular holes were closed; however, in 3 eyes, significant foveal thinning was associated with changes in the retinal pigment epithelium changes. The mean best-corrected visual acuity improved postoperatively in the majority of the patients (n: 21, mean 0.3 logMAR), stabilised in 4 patients and decreased in 3 patients (mean 0.4 logMAR). Spectral Domain-Optical coherence tomography (SD-OCT) showed resolution of the lamellar lesion and improved macular contour in all cases. CONCLUSION: We demonstrated improvement in postoperative vision and the anatomical reconstruction of the anatomical contour of the fovea in most eyes with symptomatic lamellar holes. These findings indicate that vitrectomy, membranectomy and ILM peeling with gas tamponade is a beneficial treatment of symptomatic lamellar macular holes.

[Preconceived ideas, paradoxes, and new concepts in retinal vein occlusion]. / Idées reçues, paradoxes et nouveaux concepts en matière d'occlusion veineuse rétinienne.

Retinal vein occlusion is the second cause of vascular retinopathy after diabetic retinopathy and often leads to poor visual outcome. In a simplified form, the authors attempt to rectify a number of preconceived ideas about retinal vein occlusion and introduce new concepts in order to assist in the understanding of their mechanisms. Various paradoxes are explained, such as the presence of arterial risk factors in this venous disorder, the atypical combination of retinal ischemia and the absence of vascular non-perfusion on fluorescein angiography, the fact that macular edema is larger in the ischemic form than in the well-perfused form, the aggravating role of contraceptive hormonal therapy, the protective role of substitutive hormonal therapy, etc. The current controversies are underlined: the seasonal onset of the disease, the role of vasodilator treatment, the place of etiologic screening, and the significance of prepapillary loops. Lastly, the authors summarize important basics about treatment modalities, even if there is not yet consensus on the treatment of retinal vein occlusion.

Intravitreal l-Arginine injection reverses the retinal arteriolar vasoconstriction that occurs after experimental acute branch retinal vein occlusion.

To investigate the effect of l-Arginine on the retinal arteriolar diameter following acute branch retinal vein occlusion (BRVO) in minipigs. Under general anesthesia, 10 eyes of 10 minipigs were evaluated. Two hours after BRVO, an intravitreal juxta-arteriolar micro-injection of 30 microl l-Arginine 1 mM (pH = 7.4) was performed in 7 eyes. Three eyes received a micro-injection of 30 microl of the solvent (pH = 7.4) that was used to prepare the solution of l-Arginine and served as controls. Retinal arteriolar diameter changes were measured using a Retinal Vessel Analyzer. Overall (n = 10), 2 h after BRVO there was a 10.5 +/- 1.9% decrease in the retinal arteriolar diameter in the affected territories compared to baseline (p < 0.001). An increase of 16.0 +/- 3.0% (p = 0.001) and 21.0 +/- 7.0% (p = 0.013) of the arteriolar diameter was evidenced 10 and 15 min respectively after l-Arginine injection (n = 7) compared to the diameter prior to l-Arginine injection. Thereafter, the vasodilatory effect of l-Arginine started to decrease but persisted and remained significant at the end of the study period (5.0 +/- 1.5% at 30 min, p = 0.007). Micro-injection of the solvent alone (n = 3) did not produce any significant effect on the retinal arterioles, which remained constricted at all time-points (p > 0.1). These findings demonstrate a significant arteriolar vasodilation after intravitreal juxta-arteriolar l-Arginine micro-injection in eyes with experimental BRVO in the affected territories. l-Arginine micro-injection can reverse the arteriolar vasoconstriction that occurs in acute experimental BRVO by stimulating nitric oxide production.

[Isovolumic hemodilution in the management of the acute phase of central retinal vein occlusion: a pilot study]. / Effet de l'hémodilution isovolémique dans le traitement de la phase aiguë des occlusions de la veine centrale de la rétine: une étude pilote.

INTRODUCTION: Cases series and randomized studies support the use of isovolumic hemodilution at the acute phase of the central retinal vein occlusion (CRVO). However, a recent meta-analysis showed the difficulty of interpreting the long-term effect of isovolumic hemodilution because of the late complications and the concomitant use of other treatments. We present here a pilot case-series study aiming to demonstrate the effect of isovolumic hemodilution at the acute phase of the disease, before any other treatment was applied. PATIENTS AND METHOD: Twenty-two consecutive cases of CRVO were prospectively treated with isovolumic hemodilution within 15 days of disease onset (substitution of 10 ml/kg of blood by a macromolecular solution (Voluven), aiming at a hematocrit of 35%). The treatment was performed in ambulatory conditions after excluding common contraindications (cardiac, respiratory and renal insufficiency, angina pectoris, history of heart attack or stroke during the last 6 months). The patients were followed prospectively with respect to visual acuity, fluorescein angiography and visual acuity at one week, one month, three months and twelve months. RESULTS: Visual acuity improved of at least one ETDRS line (5 letters) in 59% of the patients one week after the treatment. Improvement in the haemodynamic was observed in all these cases on fluorescein angiography. The vision remained stable at 1 month and 3 months before any other treatment was applied. After the 3rd month, additional intravitreous injection of triamcinolone was applied in 32% of eyes for persistent macular edema. At 12 months after hemodilution, visual acuity improved in 64% of cases and only 5% of the eyes converted into an ischemic CRVO. DISCUSSION: Isovolumic hemodilution at the acute phase of the CRVO is followed by an improvement in both vision and angiographic characteristics in more than 60% of our patients and the conversion into an ischemic form was limited to 5% of eyes. Further randomized studies are needed to evaluate the specific effect of hemodilution in the long term.

Retinal angiomatous proliferations: when should we suspect them and how should we detect them?

BACKGROUND: The aim of this study was to identify the clinical and angiographic features of retinal angiomatous proliferations (RAPs) in patients with age-related macular degeneration. PATIENTS AND METHODS: 26 eyes of 24 patients with RAPs were retrospectively reviewed. All patients had colour and red-free photographs, and fluorescein (FA) and indocyanine-green angiography (ICGA). The biomicroscopic and angiographic characteristics were evaluated and video-angiograms were analysed for staging the RAPs. RESULTS: The total number of RAPs was 29. Stage 1 was present in 3/29, stage 2 in 3/29 and stage 3 in 23/29 with a chorio-retinal anastomosis identified in 21 of these 23 eyes. The total number of retinal vessels involved were 83, 35 were arteries and 48 were veins. RAPs were seen in ICGA as hot spots in all but one case where it appeared as a plaque. A retinal pigment epithelial detachment (PED) was observed in 22/26 eyes. Cystoid macular oedema was observed in 13/26 eyes in FA and intraretinal ICG leakage in 6/26 eyes. Hard exudates were present in 21/26 eyes. Retinal haemorrhages were present in 23/26 eyes; all but one were intraretinal and had a size of less than half of the optic disc diameter. The RAP was bilateral in 2/24 patients. CONCLUSIONS: Clinicians should suspect the diagnosis of RAP when hard exudates, small intraretinal haemorrhages, PED or a hot spot in ICGA are present. Both fluorescein and ICG video-angiography provide adequate temporal resolution and vascular flow examination leading to easier RAP staging and identification of the anastomosis.

Bilateral multifocal retinal pigment epithelium detachments associated with systemic corticosteroids.

PURPOSE: To report an unusual case of central serous chorioretinopathy (CSC), presenting as bilateral and multifocal isolated serous retinal pigment epithelium detachments (RPEDs) following corticosteroid treatment. METHODS: An otherwise healthy 39-year-old man was evaluated for visual loss following blunt trauma of his right eye (RE). The patient underwent complete bilateral ophthalmologic examination, including optical coherence tomography and fluorescein (FA) and indocyanine green angiography (ICGA). RESULTS: At presentation, best-corrected visual acuity (BCVA) was 20/200 in the RE and 200/200 in the left eye (LE). Treatment included topical and oral corticosteroids. Three days later, the patient complained of metamorphopsia and further decrease in the VA of his RE. Fundus examination showed bilateral serous RPEDs. Optical coherence tomography, FA, and ICGA confirmed the diagnosis. Topical and oral corticosteroids were stopped and a follow-up examination 5 days later demonstrated marked resolution of the RPEDs in the RE. Five weeks later, RPEDs regressed in the RE while they persisted in the asymptomatic LE. Visual acuity in the RE further improved to 120/200. Nine months after the first visit, BCVA in the RE was 200/200. At that time, both eyes demonstrated retinal pigment epitheliopathy. CONCLUSIONS: Central serous chorioretinopathy is a known complication of corticosteroids. The classic variant of CSC consists of a shallow neuroretinal detachment located at the posterior pole of the fundus. Bilateral and multifocal isolated serous RPEDs represent an atypical form of CSC.

Congenital retinal macrovessels: description of three cases and review of the literature.

BACKGROUND: Congenital retinal macrovessels are large aberrant branches of retinal arteries or veins that cross the macula. We present three patients with a unilateral congenital retinal macrovessel and we conduct a review of the literature. PATIENTS AND METHODS: A 22-year-old man complaining of chronic headache as well as two other men, 18 and 23 years old, respectively, during a routine ophthalmological examination, were found with a unilateral congenital retinal macrovessel each. A thorough ophthalmological examination was performed, including colour fundus photography in all three patients and fluorescein angiography in two of the patients. We followed them up for five years. THERAPY AND OUTCOME: Investigation revealed a unilateral venous congenital retinal macrovessel in all patients. Clinical findings and visual acuity remained unchanged throughout the entire follow-up period. No complications were recorded. CONCLUSIONS: Congenital retinal macrovessels are rare and they tend to remain stable. Visual acuity is preserved in most cases. Complications occur only occasionally and have been described in the literature. Differential diagnosis from other arteriovenous malformations affecting multiple organs is necessary.

Evolving European guidance on the medical management of neovascular age related macular degeneration.

BACKGROUND: Until recently, only two options were available for the treatment of choroidal neovascularisation (CNV) associated with age related macular degeneration (AMD)-thermal laser photocoagulation and photodynamic therapy with verteporfin (PDT-V). However, new treatments for CNV are in development, and data from phase III clinical trials of some of these pharmacological interventions are now available. In light of these new data, expert guidance is required to enable retina specialists with expertise in the management of AMD to select and use the most appropriate therapies for the treatment of neovascular AMD. METHODS: Consensus from a round table of European retina specialists was obtained based on best available scientific data. Data rated at evidence levels 1 and 2 were evaluated for laser photocoagulation, PDT-V, pegaptanib sodium, and ranibizumab. Other treatments discussed are anecortave acetate, triamcinolone acetonide, bevacizumab, rostaporfin (SnET2), squalamine, and transpupillary thermotherapy. RESULTS: PDT-V is currently recommended for subfoveal lesions with predominantly classic CNV, or with occult with no classic CNV with evidence of recent disease progression and a lesion size

[Utility of cerclage surgery of rhegmatogenous retinal detachments: a retrospective study of 41 cases]]. / Utilité du cerclage dans la chirurgie du décollement de rétine rhegmatogène à haut risque: étude rétrospective de 41 cas.

BACKGROUND: 360 degrees encirclement for rhegmatogenous retinal detachment (RD) was introduced over 50 years ago as a method for closing retinal breaks and relieving vitreous traction. In the absence of acknowledged guidelines, current usage varies widely. PATIENTS AND METHODS: All 360 degrees encircling bands for RDs performed between 1999 and 2004 were reviewed. Encircling procedures for phakic and recurrent RDs were analysed. RESULTS: 41 encircling bands for RD were identified from the records of 875 RD cases. Median follow-up was 6 months (range: 1 - 36). Male patients accounted for 58.5 % of the procedures. Mean age was 51.51 +/- 15.97 years. 37/41 phakic and 18/41 recurrent RDs were encircled. RD recurrence in encircled eyes occurred in 42 % of phakic eyes and in 33 % of eyes re-operated for recurrent RD. At the time of recurrence, proliferative vitreoretinopathy (PVR) was present in 41.6 % of phakic eyes, and 66 % of recurrent RD eyes. Preoperative visual acuity (VA) was 0.26 and post-operative VA 0.34. Post-operative complications due to the encirclement included pain in 4 eyes, scleral abscess in 2 eyes and scleral necrosis in 1 eye. CONCLUSION: This small retrospective review highlights the multiple indications for encircling bands including PVR, inferior breaks, multiple breaks and myopia. High overall recurrence rate (34 %) reflects the selection bias of this procedure for severe disease in our series. There is currently no consensus on the use of this technique in the management of RD.

[Pseudophakic inferior retinal detachment or detachment with inferior breaks: clinical outcome and recurrences after primary vitrectomy-gas]. / Décollement de rétine du pseudophake inférieur ou comportant des brèches inférieures: résultats et récidives après vitrectomie-gaz en première intention.

BACKGROUND: This study aims to evaluate the outcome of primary vitrectomy/gas for pseudophakic retinal detachment (RD) located inferiorly or associated to inferior breaks. PATIENTS AND METHODS: We performed a retrospective, non-randomised study comprising 18 pseudophakic RD eyes with inferior RD (group A) and 19 pseudophakic RD eyes with inferior breaks (group B) treated with primary vitrectomy and gas tamponade (SF (6) 20 %). Pre- and postoperative characteristics were analysed, focusing on RD recurrences. RESULTS: In group A, RD recurred in 2/18 eyes (11 %) and was associated to proliferative vitreoretinopathy (PVR) both at first intervention and on recurrence. In group B, RD recurred in 4/19 eyes (21 %). One eye presented PVR at first intervention and all at re-intervention. Anatomic reapplication was achieved after second vitrectomy/gas in 2/4 eyes of group B, whereas long-term silicon oil tamponade was needed in 2 eyes of each group. CONCLUSIONS: This series shows a high success rate of primary vitrectomy/gas in pseudophakic RD patients with inferior RD or detachment associated to inferior breaks. Recurrences after vitrectomy are most often related to the presence of PVR.

[Recurrence after primary vitrectomy for pseudophakic retinal detachment]. / Décollements de rétine récidivants après vitrectomie en première intention chez le patient pseudophake.

INTRODUCTION: The aim of this study was to evaluate the incidence of pseudophakic retinal detachment (RD) recurrence after primary vitrectomy. PATIENTS AND METHODS: This was a prospective nonrandomized consecutive case series study, evaluating two series presenting to our clinic with pseudophakic RD from 1998 to 2004 (103 eyes of 97 patients). The study included 24 consecutive pseudophakic eyes treated with gas vitrectomy surgery with placement of an encircling band from January 1998 to December 2000 (group A) and 79 consecutive pseudophakic eyes treated with gas vitrectomy surgery with no encircling band from January 2001 to December 2004 (group B). Pre- and postoperative characteristics were analyzed in both groups. In the cases of postoperative RD recurrence, we particularly analyzed the pre- and postoperative risk factors, as well as the anatomic and functional outcome. RESULTS: Visual acuity improved in 74/103 (71.8%) eyes from both groups postoperatively. Recurrence of RD after primary vitrectomy occurred in eight of 103 (7.8%) eyes in both groups. More specifically, two of 24 (8.3%) eyes in group A and six of 79 (7.6%) eyes in group B presented a recurrence after gas vitrectomy with encircling band and gas vitrectomy alone, respectively. Among these eight eyes, four eyes (50%) presented proliferative vitreoretinopathy (PVR) at the time of initial vitrectomy, while all eyes presented PVR at the time of recurrence (one grade B, seven grade C). These eyes required two additional interventions on average. Five eyes (62.5%) required silicone-oil tamponade for a good anatomic reapplication. DISCUSSION: These results show that recurrence after primary vitrectomy for pseudophakic RD is most often related to the presence of PVR before or after the first intervention. This series reports a success rate of 91.7% and 92.4%, respectively, for group A and B, thus demonstrating the efficacy of vitrectomy in the treatment of pseudophakic RD. This study also shows a nonsignificant difference in the recurrence rate among patients treated by gas vitrectomy and those undergoing gas vitrectomy in association with encircling band placement, which raises the question of the usefulness of an additional encircling band in pseudophakic RD.

[Proliferative diabetic retinopathy: vitreo-retinal complications are often related to insufficient retinal photocoagulation]. / Rétinopathie diabétique vasoproliférante: complications vitréorétiniennes et photocoagulation rétinienne incomplète.

INTRODUCTION: Panretinal photocoagulation proved to be effective in preventing complications related to vasoproliferative diabetic retinopathy. Surgery is most often a last resort in cases of recurrent or persistent vitreous hemorrhage or retinal detachment. The aim of our study is to point out that eyes requiring surgery for complications related to vasoproliferative diabetic retinopathy are often insufficiently photocoagulated. PATIENTS AND METHODS: Retrospective analysis of operating protocols and surgical results for a series of 39 eyes of 36 patients with complications of vasoproliferative diabetic retinopathy. RESULTS: The mean age at the intervention was 57 years. Eighty-five percent of the eyes had a vitreous hemorrhage, 17% a retinal detachment. Eighty-five percent of the eyes had undergone a partial retinal photocoagulation before surgery. All eyes underwent a vitrectomy with segmentation of fibrovascular membranes. In 85% of the eyes studied, endolaser photocoagulation was necessary, sometimes even in the mid-periphery. After 39+/-26 months of postoperative follow-up, 97% of eyes showed improvement of the anatomical state of the retina and improvement or stabilization of visual acuity. CONCLUSION: Our results confirm the benefit of vitreoretinal surgery in complications related to vasoproliferative diabetic retinopathy. Moreover, it should be emphasized that complications requiring surgery often result from incomplete preoperative photocoagulation. To be effective, photocoagulation has to destroy more than 35% and up to 50% of photoreceptors. An intraoperative laser extension can reduce the risk of regrowth of fibrovascular membranes.

Regulation of optic nerve head blood flow in normal tension glaucoma patients.

PURPOSE: To investigate the regulation of the optic nerve blood flow (Fonh) in response to an increase of the perfusion pressure (PPm) in normal tension glaucoma (NTG) patients and in age-matched normal volunteers. METHODS: Measurements were performed in 16 eyes of NTG patients and in 10 eyes of age-matched controls. Laser Doppler flowmetry (LDF) was applied to calculate the relative flux of red blood cells at the temporal rim of the optic nerve head (ONH) in response to increases in PPm. PPm was raised through an increase in systemic blood pressure induced by isometric exercise. Before being tested, all patients had 3 weeks of washout of any local medication. RESULTS: In the NTG group, mean ophthalmic arterial blood pressure increased during isometric exercise from 73 to 89 mmHg (22%), resulting in a 29% increase of the PPm. This increase did not induce any significant change in mean Fonh. For the control group, the 28% increase of PPm also did not significantly affect Fonh. There was a trend for a greater increase in vascular resistance during isometric exercise in the NTG than in the normal control group (47% versus 25%). CONCLUSIONS: The LDF parameters, measured in the ONH, did not indicate an abnormal Fonh regulation in response to an increase of the PPm in either normal subjects or NTG patients. The maintenance of constant blood flow is achieved by an increase in local vascular resistance. Our data show a greater percent increase in vascular resistance in the NTG patients compared to the normal subjects for a similar percent increase in PPm in both groups during squatting. This suggests some alteration of the vessel tone regulatory mechanisms in NTG patients.

Effect of visual stimulation on blood oxygenation in the optic nerve head of miniature pigs: a pilot study.

BACKGROUND: Visual stimulation is increasingly used to investigate the coupling between neuronal activity, blood flow and metabolism in the neural tissue of the ocular fundus. In an attempt to clarify whether the oxygen metabolism is involved in this coupling, we investigated the changes in the partial pressure of oxygen of venous blood (pO (2,blood)) in the optic nerve head of pigs in response to two different visual stimuli. MATERIALS AND METHODS: In 3 miniature pigs, the pO (2,blood) was measured in the optic disk rim using the technique of phosphorescence quenching by oxygen. This parameter was recorded every 8 seconds during a dark-to-light transition and during diffuse luminance flicker (field of 30 degrees centered at the optic disk, temporal frequencies of 2 to 80 Hz). RESULTS: The venous pO (2,blood) level (mean +/- standard deviation) did not change between dark- and light-adapted conditions (26.2 +/- 5.3 and 26.0 +/- 6.2 mm Hg, respectively), nor did we observe any transient change of pO (2,blood) during the light adaptation phase. On the other hand, the venous pO (2,blood) increased, on average, relative to its level during continuous light conditions (24.5 +/- 1.9 mm Hg) by at least 6 % for all flickering frequencies, with a maximum response of 14 % at 15 Hz. CONCLUSIONS: The phosphorescence quenching technique can reveal changes in venous pO (2,blood) induced by visual stimulation. Our results show that the pO (2,blood) in the optic nerve head of miniature pigs does not change with the light adaptation state of the retina, but increases during flicker stimulation with a band-pass type response. The previously reported increase of the ONH blood flow in response to flicker stimulation could lead to this increase of pO (2,blood).

Effect of acetazolamide on the optic disc oxygenation in miniature pigs.

BACKGROUND: The purpose of our study was to evaluate the variations of the optic disc PO (2) during normoxia and hyperoxia (100 % O (2)), before and after intravenous administration of acetazolamide. MATERIAL AND METHODS: PO (2) measurements were obtained at intervascular areas of the optic disc in 11 anaesthetized miniature pigs using oxygen-sensitive microelectrodes introduced through the vitreous cavity by a micromanipulator. PO (2) was measured continuously during 10 minutes under systemic normoxia and systemic hyperoxia. Oxygen measurements were repeated under these conditions after intravenous injection of acetazolamide (bolus of 500 mg) in 8 animals. RESULTS: In systemic hyperoxia, the optic disc PO (2) increased moderately (DeltaPO (2) = 4.7 +/- 2.5 mmHg; p < 0.001; n = 11) in parallel with systemic PaO (2). Acetazolamide led to a slow and progressive increase in the optic disc PO (2) (DeltaPO (2) = 2.1 +/- 1.7 mmHg; p > 0.1; n = 8 after 10 min, while DeltaPO (2) = 4.3 +/- 3.2 mmHg; p < 0.05; n = 8 after 30 min), in parallel with a slow and progressive increase in systemic PaCO (2). The optic disc PO (2) increased much more significantly after injection of acetazolamide under systemic hyperoxia (DeltaPO (2) = 13.3 +/- 3.1 mmHg; p < 0.001; n = 8). CONCLUSIONS: Systemic hyperoxia alone is not sufficient to increase substantially the optic disc PO (2) in miniature pigs due to a vasoconstrictor effect. Intravenous injection of acetazolamide can increase the optic disc PO (2) progressively, due to a vasodilatory effect of elevated systemic PaCO (2). The association of acetazolamide injection with systemic hyperoxia can further improve the oxygenation of the optic disc.

[Experimental branch vein occlusion: the effect of carbogen breathing on preretinal PO2]. / Occlusion veineuse rétinienne expérimentale: effet de l'inhalation de carbogène sur la PO2 prérétinienne.

PURPOSE: To evaluate the variations in preretinal PO2 in normal and in ischemic postexperimental branch vein occlusion (BRVO) retinal areas during normoxia, hyperoxia (100% O2) and carbogen (95% O2, 5% CO2) breathing. METHODS: Preretinal PO2 measurements were obtained in intervascular retinal areas far from the retinal vessels of 13 anesthetized miniature pigs with oxygen-sensitive microelectrodes (10 microm tip diameter) introduced through the vitreous cavity by a micromanipulator. The microelectrode tip was placed at 50 microm from the vitreoretinal interface in the preretinal vitreous. PO2 was measured continuously for 10 minutes in systemic normoxia, hyperoxia (100% O2 breathing) and carbogen (95% O2, 5% CO2) breathing. A BRVO was induced with an argon green laser, and oxygen measurements were repeated in normoxia, hyperoxia and carbogen breathing. RESULTS: In hyperoxia, preretinal PO2 remained almost constant in both normal retinas (DeltaPO2=1.33 mmHg +/- 3.39; n=13) and ischemic retinas (DeltaPO2=3.73 mmHg +/- 2.84; n=8), although systemic PaO2 significantly increased. Carbogen breathing induced a significant increase in systemic PaO2 and PaCO2. Furthermore, it significantly increased preretinal PO2: DeltaPO2=23.05 mmHg +/- 17.06 (n=12) in normal retinas, and DeltaPO2=22.54 mmHg +/- 5.96 (n=6) in ischemic retinal areas. CONCLUSIONS: Systemic hyperoxia does not increase preretinal PO2 significantly in normal and ischemic post-BRVO retinal areas of miniature pigs, as hyperoxia induces a decrease in the retinal blood flow. Carbogen breathing significantly increases preretinal PO2 in normal and in ischemic post-BRVO retinal areas. This effect is probably due to the vasodilatation of the retinal arterioles induced by the intravascular PaCO2 increase.