Extended depth of focus (EDOF or EDF) intraocular lens (IOL) or Extended range of focus is a new type of lens used in the treatment of presbyopia. Presbyopia refers to a condition that results from age where the lens starts to lose its elasticity resulting in farsightedness. The lens is implanted in the course of cataract surgery to remove a cloudy cornea. When a lens gets clouded, it can cause a hazy, blurry vision with less color perception.
EDOF lens has several advantages over the monofocal and multifocal intraocular lens. First, an EDOF intraocular lens offers better intermediate performance. Monofocal and multifocal intraocular lens tend to provide excellent distance vision but unsatisfactory near or intermediate vision since they cannot correct all three vision distances at once.
Secondly, an EDOF lens offers less light scatter than a monofocal lens. Besides, it presents smaller halos than a multifocal lens. With an EDOF lens, there is no ‘dip’ between intermediate and distance vision. Generally, an EDOF lens has less visual side effects than a monofocal or multifocal lens.
The EDOF lens is an emerging technology with ongoing EDOF IOL trials. The TECNIS Symfony IOL from Abbott Medical Optics, California, was the first EDOF to be approved in America and it is currently in use.
An EDOF lens works by creating a single elongated focal point to enhance depth of focus or range of vision. This elongated focus minimally affects peak resolution, hence offers a clear vision at different distances. It combines the benefits of both monofocal and multifocal lens. The resultant clear, sharp vision enables normal daily activities such as sports, watching TV, cooking, cleaning, working on the computer, etc. Glasses may only be necessary for reading and other fine precision tasks requiring glasses. To improve reading and attain independence from glasses, the doctor can combine the use of the EDOF lens and monovision.
Doctors recommend the EDOF lens for patients who want the freedom to live an active lifestyle with no or minimal dependence on eyeglasses or contact lenses. This means they want distance as well as near and intermediate vision. All IOLs with an emmetropia offer good distance vision at 6m/20 feet. With the EDOF lens, an increase in power from 66cm/26in to 50cm/20in will add intermediate vision. The doctor can also adjust measurements for near vision thus giving the patient vision from all distances.
An EDOF lens has the least visual side effects compared with the rest of the IOLS. These include less glare, halo, less light scatter, etc. However, like every other cataract surgery, there may be complications or risks involved such as:
- Chronic inflammation (swelling) of the eye can occur. The swelling can cause further complications.
- Photopsia can occur. Photopsia is the presence of perceived flashes of light. They are also referred to as floaters.
- Ptosis (droopy eyelid) occurs when the upper eyelid droops over the eye. Severe ptosis can block normal vision.
- Macular edema occurs when fluid builds up in the central region of the retina. This causes the macula to swell and thicken leading to distorted vision.
- Infection, pain in the eye, decreased vision and bleeding may result from the surgical procedure. These complications can lead to permanent loss of vision or even loss of the eye.
- Lens dislocation can occur which necessitates further surgery with additional risks. The surgeon can put the lens back in position, exchange it with a new one or remove it altogether.
- There may be an increase in intraocular pressure (IOP). Increased pressure could give rise to glaucoma. Glaucoma is a severe condition that can lead to vision loss or total blindness. Patients with glaucoma require lifelong medication.
- A retinal detachment can occur. The retina is tissue that lines the back of the eye and is sensitive to light. When the retina pulls away from its position, it is called a retinal detachment. If not treated, a retinal detachment can cause loss of vision.
An EDOF lens is stored in a vapor-permeable package. It is usually kept in a relatively dry environment and at room temperature. Research indicates that the context in which the lens is stored determines its effectiveness. Studies show that spraying an environment where the lens is stored can lead to surface changes to the lens. When spraying to disinfect or clean a storage room, the lens should be transferred to a safer environment with no chemicals.