What is Presbyopia?
As we enter our forties, the natural human lens that sits behind the pupil begins to lose its ability to focus from distance to near. Presbyopia is the medical term for this ocular condition. The process continues to worsen through our fifties and then reaches the endpoint of the lens not being able to focus at all. People with presbyopia begin to wear reading glasses or bifocals if they have a refractive error for distance vision.
History of Scleral Implants for Treating Presbyopia
The initial FDA study or Phase I was started in 2000. The Phase II FDA study was started in 2004 and included the use of an automated scleratome to create a standardized size and shape scleral tunnel. Phase I had shown variations in surgical techniques by different surgeons.
The Phase III FDA study was started in 2005 and at that time both eyes could be treated. The study was suspended at the end of 2006 due to the new technology of optical coherence tomography showing the twenty five percent of scleral implants were moving or displacing. At least seventy five percent of patients had at least one of the scleral implants displaced. This resulted in diminished presbyopic correction.
In 2009, the FDA study was resumed with a newly designed two-piece locking mechanism that holds the scleral implants in place.
The Refocus Group that manufactures the PreView™ Scleral Implant hopes the new procedure will receive FDA approval by 2014.
Scleral Implant Design
The PresView Scleral Implant is designed in two segments with a wide foot plate on the end. It is made of PMMA polymer and is cosmetically acceptable.
The Theory of Action for the Scleral Implants
As we age the natural human lens inside the eye continues to gradually enlarge in size over time. The distance between the edge of the lens and the ciliary muscle (muscle that pulls on the lens to change its shape to focus) becomes less. This is believed to contribute to the development of presbyopia and glaucoma. The scleral implant works by lifting up on the sclera (white portion of the eye) and the ciliary muscle underneath the sclera. This increases the distance between the lens and the ciliary muscle. The increased tension on the lens by the zonules (attach the ciliary muscle to the lens) allow the ciliary muscle to manipulate the lens increasing the ability of the lens to focus.
The procedure is done with local anesthesia in an operating room. A device to keep the eyelids open is put into place. The conjunctiva (the outer layer of tissue that overlies the sclera or white portion of the eye) is opened to expose the sclera. A ring is attached to the eye with suction to give the surgeon control of the eye. A specialized instrument is used to create four tiny scleral tunnels in the sclera in a circular pattern around the eye. The tunnels are four mm long, 1.5 mm wide, and 400 microns deep. The two-piece scleral implants are placed inside the scleral tunnels and locked in place. The suction ring is removed. The conjunctiva is sutured back in place. The procedure takes about twenty to thirty minutes to complete. It takes about three or four weeks for the eye to heal.