Collagen corneal shields refer to disposable, short-term corneal bandage lenses used after surgery to protect the ocular surface. The lenses were first developed in 1984 by Fyodorov after photorefractive surgery and radial keratotomy. Previously, doctors used rigid poly methyl-methacrylate (PMMA) scleral contact lenses in various clinical circumstances. The use of hydrogel bandage contact lenses followed before introducing collagen as an agent for healing wounds when managing burns and skin ulceration.
Collagen corneal shields are manufactured from porcine or bovine scleral collagen, which conforms to the cornea when placed on the eye, eliminating the need for multiple base curves. The shields take the shape of a contact lens. They are manufactured in a dehydrated form, therefore requiring rehydration before they are inserted.
Collagen carries the advantage of biocompatibility and biodegradability. It also offers support to the corneal epithelial cells in culture; it is therefore considered ideal for making collagen corneal shields. However, manufacturers are advised not to use collagen corneal shields on patients with diseased or infected corneas. Studies in this area are still ongoing.
There are three types of collagen shields (Type 1, 2, and 3), which dissolve to varying rates of 12, 24, and 72 hours respectively, depending on collagen cross-linking. The shield dissolves when the tear film undergoes proteolytic degradation.
Collagen corneal shields have the following uses:
Ocular surface lubrication
Because collagen is a protein that occurs naturally, it carries the advantage of safety in the body. The shields will dissolve and eventually liquefy. Research indicates that the gel-like dissolution property of these shields is beneficial to patients with dry eye syndrome (don't produce enough quantities of tears). Dry eye is a potentially damaging condition for the eye, with patients having to use artificial tears (eye drops) every 30 to 60 minutes. With collagen corneal shields, patients do not have to use artificial tears.
Research indicates that collagen corneal shields can help with drug delivery, where the shield is used as a sponge.
Topical medications (in drop form) together with the shield are placed on the ocular surface so that as the shield dissolves, there is a slow release of the medication over time. Drugs may be integrated into the collagen matrix during the manufacturing processes, absorbed into the shield in the rehydration process, or applied topically with the shield in the eye. Studies also indicate that the high concentrations of drugs released from the collagen shield can effectively treat a variety of eye diseases such as ocular surface inflammation and infections.
The slow release of the drugs is also helpful to patients with potentially sight-threatening diseases managed through frequent administration of eye drops. Further studies reveal that drug delivery is best when the collagen shields are pre-soaked in a pharmacological agent with adjunctive therapy. Collagen corneal shields may enhance epithelial and stromal healing and drug delivery in microbial keratitis. They also neutralize collagenases and reduce corneal inflammation.
Ocular surface protection
Most eye surgery types make use of incisions on the cornea or sclera (surface coat) to allow the surgeon access into the interior part of the eye. Surgical success will depend on how the wound heals. Some surgical procedures are done on account of trauma to the eye; therefore, the wound needs adequate protection from blinking and from the outside environment. This protection often comes in the form of a patch in the initial stages after surgery.
Some surgeons have also used bandage contact lenses to protect the ocular surface. However, when used for long periods, bandage contact lenses present with certain complications besides being expensive. Though research is ongoing concerning the healing properties of collagen corneal shields, current results indicate that they can deliver an acceptable protective environment for the surgical and traumatic eye wound to heal.
Improve wound healing
Research is ongoing on whether collagen corneal shields can cause better and faster wound healing. It is thought that collagen is a natural protein and can therefore be incorporated into a healing wound on the eye's surface, through the shield.
The shields are rehydrated for 3 minutes in saline, antibiotic, steroid, lubricating solution before application. The surgeon may need to apply topical anesthetic. A drug like cyclosporine may be incorporated into the shields at the time of manufacture if the purpose is to help with drug delivery. The shields are entirely soluble so that they don’t need removal from the site of application. Antibiotics are applied to the eye in cases like bacterial ulcers, post-PK, etc.
Disadvantages of Corneal Shields
Collagen corneal shields may not be optically clear, and the collagen may cause the patient some level of discomfort in the eye.