RECENT ADVANCES IN VITREOUS SURGERY 

by Stanley Chang, M.D.

(CAMS 1999 Scientific Award Lecture)

The vitreous plays a significant role in the pathogenesis of many retinal disorders such as diabetic retinopathy, retinal detachment, and macular abnormalities. Opacities develop from bleeding in diabetic retinopathy or trauma. The vitreous is adherent to the retina in youth, and separation of the vitreous as a result of aging may result in retinal tears or detachment. Tractional changes along the vitreoretinal interface
may also result in surface changes which cause retinal detachment or loss of vision.

In 1970, Machemer reported the successful removal of longstanding vitreous hemorrhages in a group of diabetic patients. Over the next three decades refinements in surgical techniques have expanded the indications and capability of vitreous surgery. Some of the advances are the use of long-term vitreous replacements, endolaser photocoagulation, panoramic viewing systems, and perfluorocarbon liquids.

Vitrectomy continues to be the only method for restoring vision in advanced forms of proliferative diabetic retinopathy. The vitreous acts as a scaffold for fibrovascular tissue to grow along the retinal surface at the vitreoretinal juncture. This tissue contains collagenous and vascularized tissue which may bleed causing vitreous hemorrhage or contract resulting in tractional retinal detachment. The fibrovascular
tissue is stimulated by cytokines which are released from ischemic retina, such as vascular endothelial growth factor (VEGF). The surgical goal is to remove vitreous opacities, and the fibrovascular proliferation as completely as possible. This is done through three small (20 gauge) pars plana incisions entering the vitreous space. An infusion line is placed to restore fluid which is aspirated by a vitreous cutter.
Fiberoptic endoillumination is used to illuminate the eye allowing visualization of intraocular structures through the pupil and lens.

Microscissors, forceps and diathermy for cauterization of bleeding have been developed as adjuncts to the primary instrumentation. Currently vitrectomy in diabetics with advanced retinopathy resulting in loss of ambulatory vision is successful in improving vision in 85-90% of eyes. Because the surgical procedure removes the scaffold for future proliferation, vitrectomy has a stabilizing effect on the retinopathy, and usually stops its progression.

Wide field or panoramic viewing sysytems have also improved the visualization of vitreoretinal anatomy during surgery. Traditional plano-concave contact lens have been used for fundus viewing for over two decades. These lenses neutralize the optical power of the cornea but only provide a 20-30º field of view, essentially around the posterior structures such as the vascular arcades, and macular area. The
introduction of panoramic viewing systems used the optical principles of indirect ophthalmoscopy creating a virtual image with high plus condensing lenses. This technique results in image inversion, but a a large field of view up to 130º. The image is reverted by a prism system mounted on the surgical microscope.

Complex retinal detachments form a group of retinal detachments which are best managed with vitrectomy. Improvements in surgical techniques have resulted in success rates of over 90% for these forms of retinal detachments. The most common cause for failure of retinal detachment surgery is the development of fibrous proliferation on all surfaces of the retina, a process called proliferative vitreoretinopathy (PVR). This results in stiffening of the retina caused by fixed retinal folds, and shortening of the retinal dimension so that it will not reattach to the choroidal surface. The epiretinal membranes which grow on the retina, are delicately peeled from the surface of the retina, allowing increased mobility of the tissue. Another form of complex retinal detachment best managed with vitrectomy is giant retinal tears. This is defined as a tear involving more than 90 of the retinal circumference. Often the retina becomes folded onto itself, and must be unfolded
intraoperatively. In previous years, the patients were turned into the prone position during surgery so that an air bubble could be used to manipulate the retinal tear and flatten it.

The introduction of perfluorocarbon liquids (PFCL) resulted in a greater ability to manage complicated forms of retinal detachment. These liquids are clear and have a specific gravity also twice that of water. When injected into the eye, the PFCL flattens the retina, and stabilizes it. Thus a large retinal tear can be easily manipulated and reattached intraoperatively. Similarly, in PVR, the PFCL flattens the retina, allows
better visualization of tractional relationships and greater ease of removal of epiretinal membranes. These liquids are only used as an intraoperative tool, and should be removed at the end of the surgical procedure.

Macular surgery has increased in recent years allowing improvement in central vision. Macular pucker is a focal proliferation of proliferative tissue in the macula causing a reduction of visual acuity. A macular holes is a full thickness defect in the foveal area which often reduces vision to the level of 20/200. Vitrectomy has been able to improve vision in the patients in 85-90% of patients with these conditions.
More recently, a surgical approach has been tried in choroidal neovascularization, which complicates conditions such as age-related macular degeneration, presumed ocular histoplasmosis syndroe, and high myopia. The surgery is done by making a small access retinotomy into the subretinal space, followed by extraction of the neovascularization using microforceps. The visual results have been modest, but in many cases, the disease process is stabilized. The modest improvements in visual acuity has led to interest in macular translocation in which the retina is detached and shifted so that the macula settles onto a more healthy area of choroid. Refinements in this surgery are currently in progress.

Dr. Chang is Edward S. Harkness Professor and Chairman of the Department of of Ophthalmology, Columbia University.