Definition of an Intraocular Lens
Anatomy of the Lens
Cataracts are the most common cause of blurry vision in patients over the age of 55. Although glasses can compensate for the loss of vision for a while, eventually surgery will be needed to restore clarity.
This surgery involves the removal of the lens, a structure found behind the iris that is densely packed with cells contained inside a bag known as a capsule.
This capsule is suspended by little filaments called zonules that are attached to the ciliary body, a muscle that produces aqueous. These filaments allow the lens to bend and flex in order to focus on objects at different distances. This is how we are able to read and see things like our dashboard when we’re driving.
As we age, the lens begins to harden, which causes blurry vision, problems reading up close and problems driving at night among other things. The lens also begins to yellow, which can cause distortions in color perception and contrast sensitivity. Other symptoms caused by a cataract include:
- Blurry, hazy or foggy vision
- Inability to read at close range
- Difficulty seeing a computer screen or vehicle dashboard
- Glare from lights (both headlights and traditional lighting)
- Problems driving at night
- Vision that seems dim, or dark
The History of the Intraocular Lens Implant or IOL
An IOL is a device implanted into the eye to correct vision after a cataract is removed. During cataract surgery, the lens is removed and an implant, or intraocular lens (IOL), is put in its place.
The implant was discovered in the 1940s, by a man named Harold Ridley. Ridley was an ophthalmologist who became a member of the Emergency Medical Service, after serving a year in the Royal Navy.
During WWII, specifically the Battle of Britain (Germany’s air attack), Ridley saw Royal Air Force pilots with eye injuries involving fragments of the cockpit canopy of their planes.
The canopy was made of a material known as polymethylmethacrylate, or PMMA, a very hard plastic. The PMMA shards caused no symptoms of rejection in the injured eyes. This gave him the idea for the implant.
The first intraocular lens was implanted in February 1950. Lenses were attached to the iris inside the pupil, called an iris clip, up until the late 1970s. These served their purpose, but unfortunately, the eye could not be dilated or the lens would rip the iris and fall back into the vitreous.
This led to the haptics we use today. Haptics allow the IOL to be placed inside the capsule, and prevent movement. IOLs can also be placed in the anterior chamber (in front of the iris); however, this usually only occurs if the capsule is damaged in some way, or the ophthalmologist feels the capsule won’t hold the lens sufficiently.
Types of Lenses
Until recently, there was only one type of implant. This “standard” implant is single focus, meaning the patient can see clearly at distance, but will need glasses for reading up close and working on a computer.
However, intraocular implants have evolved. There are now several different classes of lenses on the market, and there are several different lenses in each class (with exception of two). The classes are:
- Monofocal lenses - these are the standard implants that have been used since the inception of the IOL.
- Multifocal lenses - these implants allow patients to see at distance and near and just about everything in between. There are a few different types of multifocal lenses.
- High definition lenses (for patients who drive at night)
- Accommodating lenses
There is something for just about everyone, and all different lifestyles. It's important to talk with your physician to determine if you are a candidate for multifocal or accommodating lenses.
Typically, patients with retinal pathology such as macular degeneration are not good candidates because they will not reap all of the benefits the lens has to offer.
Before reading this hub, did you know there were so many different IOLs?
The Standard Monofocal Implant
The standard implant only corrects vision at distance, requiring the patient to use reading glasses, or readers, for any type of near work. Some patients will need correction for distance as well, especially if they have astigmatism (irregular corneas) or the pre-surgery measurements were not done correctly.
Multifocal implants allow patients to read at distance, intermediate and near ranges. There are two main types of these lenses:
The ReSTOR multifocal lens is designed like the Monofocal lens, however the center of the implant has a concentric ring pattern that allows for reading at intermediate and near distances. This lens had issues with glare at night when it originally came out. Alcon says it has resolved this issue with its new aspheric ReSTOR Lens.
The ReZoom lens is similar to the ReSTOR lens with the exception that it has five concentric rings at varying distances for intermediate, near, distance and night driving vision. This lens is better for patients who do things at an intermediate distance regularly.
Lenses for Night Driving - The Technis Aspheric Lens
This lens was designed for patients who frequently drive at night. Studies have shown the Technis lens gives an extra ½ second of reaction time at night because the patient can see a few feet farther than a traditional Monofocal lens.
It is the only lens that is designed to compensate for spherical aberrations in the cornea that lead to glare and halos from oncoming car lights at night. It uses wavefront technology, the same technology used in high definition LASIK.
Accommodating Lenses - The Crystalens
I’m a bit biased on this one. The Crystalens is an accommodating lens implant. This means it uses the eye’s natural muscles, the little filaments known as zonules, to focus the lens at all distances.
Why am I biased? Because, the theory behind the lens is sound, and it allows for a greater range of vision among varying distances compared to the multifocal lens.
There is also no chance for issues with glare at night because there are no concentric rings to create halos. This is as close as we can humanly get to the original lens Mother Nature gave us.
However, there are a couple of drawbacks to this lens. For the first week after surgery, the patient is not allowed to read. In fact, the eye will usually stay dilated for a week after surgery to prevent possible accommodation. This is to allow the lens to seat properly in the capsule.
If the patient were to read the first week, the lens could bow forward and stay there, causing the patient blurry vision at all distances and the benefit of the lens would be lost completely.
The other drawback is the zonules. These little muscles that focus the lens have atrophied since the formation of the cataract. It takes up to six months to build these muscles back up and realize the full value of the Crystalens. However, there are exercises the patient can do to facilitate this process.
It is recommended that patients have their second cataract surgery as close to the first one as possible when opting for the Crystalens. This allows both eyes to work together more easily and allows the patient to strengthen the zonules in both eyes at the same time.
These lenses correct astigmatism. Astigmatism is a fancy medical term for an irregular or bumpy cornea.
This lens allows patients, who would otherwise have to wear glasses to correct this, see things at distance without glasses. There is no multifocal version of this lens as of yet; however, there is an accommodating version of the toric lens called a Trulign lens.
Choosing an IOL
There are a number of things to consider when choosing an implant. The most important thing to do is to discuss it with your ophthalmologist because he or she can tell you if you are a candidate for one of the multifocal or accommodating implants.
Most patients who have any type of retinal pathology such as macular degeneration or diabetic retinopathy are better suited for the standard implant. Because of the damage to their retinas, they will be unable to experience the full range of benefits the premium lenses have to offer.
There are also the risks to consider. Although these implants very rarely have problems, there is always the risk of complications. There is no guarantee that you will have perfect vision after the procedure. This is another reason it is imperative for you to discuss your decision with your ophthalmologist.
Another thing to consider is cost. These premium lenses come at an extra cost. Knowing that there is a risk involved, it’s important to weigh the risks and benefits to determine if the lens is worth the cost.
Questions & Answers
Can intraocular lenses ever be replaced?
Intraocular lenses don't need to be replaced. In some cases, a procedure known as an IOL exchange can be done, but this is usually only done as a last resort if the wrong implant was used. If you're having problems with your vision after cataract surgery, you may need a YAG capsulotomy to restore vision.
After cataract surgery, you can experience what is called a secondary cataract that has very similar symptoms to a cataract. The capsule that holds the implant tends to scar after cataract surgery, it's part of the healing process and happens to everyone at some point. We can treat this by using a YAG laser to put a hole in the scar tissue so you can see clearly again.
© 2013 Melissa Flagg OSC