Effects of pars plana vitrectomy on retrobulbar haemodynamics in diabetic retinopathy

BACKGROUND

The purpose of the present study was to determine the effects of pars plana vitrectomy on retrobulbar haemodynamics in patients with proliferative diabetic retinopathy (PDR).

METHODS

Colour Doppler imaging was used for measurement of blood flow velocities and resistive index of the ophthalmic artery (OA), posterior ciliary arteries (PCA) and central retinal artery (CRA) in 14 eyes of 14 patients with PDR before pars plana vitrectomy and at the 1 and 6 months after operation. The patients were also treated by laser photocoagulation before or during surgery. Twenty age- and sex-matched healthy subjects were used as control group.

RESULTS

Mean peak systolic velocity and the end diastolic velocity of the CRA in the patients with PDR were lower and the mean resistive index was higher than in those of the control group (P < 0.05). The mean end diastolic velocity of OA in the patients was lower and the mean resistive index was higher than in the control group (P < 0.05). The peak systolic velocity of the OA and the end diastolic velocity of the CRA were significantly increased (P = 0.043 and P = 0.018, respectively) and the mean resistive index of the CRA was significantly decreased after pars plana vitrectomy (P = 0.043). No significant changes were detected among preoperative and postoperative values of peak systolic velocity, end diastolic velocity, and resistive index of the PCA and the mean velocity of the central retinal vein (P > 0.05).

CONCLUSIONS

The blood flow velocities of OA and CRA are decreased but the resistive index is increased significantly in patients with PDR. Pars plana vitrectomy in patients with PDR may decrease resistive index and improve blood flow in the CRA.

Neovascularization in the anterior segment of the rabbit eye by experimental anterior ischemia

PURPOSE

To investigate the effects of anterior ischemia accompanied by neither retinal nor choroidal ischemia on the anterior segment of the eye.

METHODS

Both long posterior ciliary arteries in the right eye of 14 rabbits were directly cauterized with an electric coagulator. The eyes were enucleated 1, 2, 4, 7, 9 or 14 days after cauterization, then fixed with 4% paraformaldehyde. Semi-thin sections were studied by light microscopy. Several sections were stained with Griffonia simplicifolia lectin, which bound specifically to mammalian vascular endothelium. Other specimens were examined immunohistochemically for vascular endothelial growth factor (VEGF) protein. The tissue specimens of the first postoperative day were studied for expression of VEGF mRNA by in situ hybridization.

RESULTS

Atrophy of the iris and ciliary body was seen after the second postoperative day. Corneal neovascularization appeared after 7 days. Neovascularization on the anterior surface of the iris and in the trabecular meshwork was detected after the ninth postoperative day. The proliferative tissues with newly formed vessels obstructed the iridocorneal angle 14 days after the treatment. There was no histological change in either the retina or choroid. Immunohistochemically, VEGF protein was detected in the epithelial and vascular cells of the iris on the first and fourth postoperative day. Expression of VEGF mRNA was detected in the epithelial cells of the ciliary body on the day following the treatment.

CONCLUSIONS

Anterior segment ischemia, when unaccompanied by retinal ischemia, causes neovascularization in the cornea, iris and trabecular tissue.

Anterior segment ischemia after strabismus surgery with microvascular dissection

Anterior segment ischemia is a rare but well-known complication of extraocular muscle surgery.(1) Several surgical techniques have been used to prevent this complication in high-risk patients. A number of studies have suggested that microvascular dissection and preservation of the anterior ciliary vessels during strabismus surgery may reduce the risk of ischemic complications. (2-4) We present a case in which anterior segment ischemia occurred despite the use of this vessel-sparing technique.

Aqueous vascular endothelial growth factor increases in anterior segment ischemia in rabbits

Both long posterior ciliary arteries were occluded or the three extraocular muscles were tenotomized to produce anterior segment ischemia in rabbits, and the aqueous levels of vascular endothelial growth factor (VEGF) were measured. The occlusion of both long posterior ciliary arteries led to clinical and histological anterior segment ischemia in varying degrees. The aqueous VEGF levels increased significantly compared with controls on all days examined (Mann-Whitney U test: day 1, P = 0.0039; day 4, P = 0.0065; day 7, P = 0.0039; day 14, P = 0.0104), while the levels at days 7 and 14 decreased significantly compared with those at day 4 (Wilcoxon signed-rank test; day 4 to day 7 and day 4 to day 14, P = 0.0464). In contrast, tenotomy of the three extraocular muscles resulted in no histological changes. The VEGF levels increased significantly compared with controls at day 1 and day 4 decreased significantly compared with those at day 1 (Wilcoxon signed-rank test, P = 0.0499). Aqueous VEGF levels represent the severity of anterior segment ischemia and could be used as an indicator for the extent of ischemia.