Phakic intraocular lens (IOLs) are contact lenses that are implanted into an eye through surgery. Also known as implantable contact lenses (ICLs), phakic lens are fixed between the cornea and the iris. The natural lens is not removed. They can be inserted behind the iris too. Once fixed, they are not noticeable.
IOLs treat myopia (nearsightedness) in patients whose vision cannot be corrected by glasses, contact lenses or laser surgery. Usually the cornea is too thin to allow a laser procedure. Or it may be scarred or have an irregular shape; hence laser surgery would not be ideal. The IOLs enable light to focus correctly on the retina thus providing excellent quality of vision. They function like contact lenses but unlike the conventional contact lenses, phakic lens function from within the eye as opposed to the surface of the eye. They offer a permanent solution to myopia.
Myopia is a refractive error that occurs when the eye grows too long from front to back. The result is that the lens focuses the image in front of the retina instead of on the retina. Myopic patients have good near vision but reduced distance vision.
Types of Surgery
There are two broad categories of phakic IOLs:
- Anterior chamber intraocular lens (ACIOLs), further divided into angle-supported ACIOLs and Iris-claw ACIOLs
- Posterior chamber intraocular lens (PCIOL). The Visian ISL is a subtype of PCIOL.
In America, the angle-supported ACIOL and Visian ISL are Food and Drug Administration (FDA) approved. More trials are ongoing for other phakic lens such as the ThinPhAc and Vision Membrane among others.
Implantable IOLs are recommended for patients with severe myopia that has defied the use of glasses, contact lenses and laser surgery. Patients with mild to severe ametropia can also use them. Ametropia is a refractive error where images fail to focus on the retina.
Doctors will determine the right lens for each individual. Companies that make lenses often provide software that calculates the correct lens after feeding it with a patient’s measurements. For instance, to calculate ACIOL power, a Van de Hejde nomogram is used. The doctor will input the patient’s anterior chamber depth (ACD), keratometry and refraction. A Binkhorst nomogram will calculate PCIOL power. It will also require a patient’s ACD, spectacle plane refraction and the cornea’s power. The ideal phakic power is between 0.5-1.0 D of emmetropia that’s close to achieving a 20/20 vision.
After Care, Recovery, Results
The following are the possible side effects of IOLs:
- The patient can develop symptoms such as double vision, halos and glare. There may also be reduced vision where lighting is dim. The patient then experiences difficulties like driving.
- Sometimes the lens may shift from its position. In this case, further surgery may be required to reposition the lens. Or it could be that the lens had the wrong power so that a new surgical procedure is necessary. The IOL may also be of the wrong size or cause debilitating visual symptoms. Surgery is required to improve vision but it may carry its own risks.
- The patient may develop increased intraocular pressure (IOP). Increased pressure may cause glaucoma. Glaucoma is a severe condition that can lead to vision loss or total blindness. With glaucoma, the patient will require lifelong medication.
- The cornea can get cloudy. The endothelial cells in the cornea perform an essential function of getting rid of fluid in the cornea to keep it clear. IOLs implantation result in the decrease of endothelial cells at a faster rate than usual. When the number of these cells drops so low, a cloudy cornea can arise leading to loss of vision. This problem can further be corrected by a corneal transplant.
- Cataract development is another risk. A cataract refers to the clouding of the natural lens. Cataract surgery is required to remove both the phakic and cloudy natural lens.
- A retinal detachment can be a risk of phakic lens implantation. 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 gives rise to a retinal detachment. If not treated, it can cause loss of vision.
- Infection, pain in the eye, decreased vision and bleeding may result from an IOL surgical procedure. These complications can give rise to permanent loss of vision or even loss of the eye.
Overcorrection & Undercorrection
The power of the IOL may be too strong or too weak leading to under treatment or over treatment. This is a consequence of the difficulty in determining accurate measurements for the IOL. The patient can either have a repeat surgery or wear glasses or contact lenses to perform some tasks. For example, some patients will need glasses even if they were not using them before.