The vitreous body is a clear, transparent gelatinous substance in the vitreous cavity of the eye that is posterior to the lens and anterior to the retina. The vitreous body occupies two thirds of the ocular volume, having a weight of approximately 4 g and a volume of about 4 mL. The main components of the vitreous body include water (98%), collagen fibrils, glycosaminoglycans, and hyaluronic acid (HA). It functions to give shape to the eye, transmit light, and form a semi-solid support scaffold for the retina. Specific diseases, age-related degeneration, and/or trauma can lead to pathological changes in the vitreous body, including HA degeneration and collagen precipitation, which may result in liquefaction of the vitreous matrix. A degenerated or liquefied vitreous body can lead to floater formation (e.g., cellular debris and deposits of various size, shape, consistency, refractive index, and motility within the eye's normally transparent vitreous humor which can obstruct vision), posterior vitreous detachment, epimacular membrane macular schisis, macular hole, vitreomacular traction, and possible retinal breaks and detachment, all of which may result in a loss of vision.
Vitrectomy is surgery to remove some or all of the vitreous humor from the eye. The original purpose of vitrectomy was to remove clouded vitreous from the eye. Among clinical treatments today, pars plana vitrectomy (PPV) is a common surgery for treating a number of ocular diseases, including diabetic retinopathy, retinal detachment, vitreous hemorrhage, and macular holes. During PPV, the vitreous body is cut and aspirated out of the eye, and then (after additional surgical steps if needed) may be replaced with a vitreous substitute such as gas (air, perfluoropropane, or sulfur hexafluoride) or silicone oil. Vitreous substitutes are used to fill the vitreous cavity and help reattach the retina after surgery. Postoperatively, a vitreous substitute can keep the retina in position while the adhesion between the retina and the retinal pigment epithelium cells forms.
Considerations for vitreous substitutes include clarity, transparency, refractive index similar to natural vitreous humor, ability to allow metabolite transfer, non-absorbable characteristics, hydrophilic composition, and the ability to be injected through a small-gauge needle. Moreover, the substitute should be generally non-toxic, non-inflammatory, and non-immunogenic without being easily degraded or decomposed. Thus, it has been challenging to provide a suitable vitreous substitute.
Dispersive ophthalmic viscoelastics (OVDs) are frequently used to maintain the clarity and integrity of the globe during vitrectomy procedure. However, studies have shown that OVDs may cause or aggravate glaucoma if left in the eye too long and OVDs diffuse out of the eye. Infusion fluids such as balanced salt solution (BSS or BSS Plus) cannot supply long-lasting vitreous substitutes because they are replaced within hours. Gases injected into the posterior segment of the globe are useful for flattening a detached retina against the globe and keeping it attached as healing occurs. However, gases can raise the intraocular pressure, causing possible occlusion of the central retinal artery. Contact of the gas with the lens can induce cataract formation, and contact of the gas with the corneal endothelium can cause corneal damage. Gases are also rapidly reabsorbed from the vitreous cavity within a few days. Rapid elimination prevents the gases from supporting the retina long enough to promote effective healing. In addition, it is often necessary for the patient to maintain an uncomfortable prone position for a week or more following surgery when gas is used to prevent pupillary block glaucoma. Silicone oil has been used instead of gases for complicated retinal detachments or in patients (e.g., children) who are unable to maintain such positioning post-operatively, but silicone oil self-emulsifies (requiring removal and possible retinal detachment) and long-term complications from the silicone oil can include cytotoxicity to ocular tissue, cataract, and emulsification glaucoma. In addition, most of the current vitreous substitutes lack hyalocytes, hyaluronan, ascorbic acid, and other factors that are present in vitreous humor. Some of these factors, particularly ascorbate, may function to prevent nuclear sclerotic cataract formation, which is partly due to oxidation reactions, via their anti-oxidant properties.
Accordingly, there exists a need for an improved vitreous substitute. The systems and methods disclosed herein overcome one or more of the deficiencies of the prior art.