A posterior chamber intraocular lens (IOL) is a type of artificial lens that is implanted in the eye to replace the natural lens that has been removed during cataract surgery. Cataract surgery involves removing the cloudy lens of the eye, which is typically replaced with an intraocular lens to restore clear vision. The posterior chamber refers to the space behind the iris (the colored part of the eye) and in front of the vitreous humor (the gel-like substance filling the back of the eye).
The placement of a posterior chamber IOL involves a surgical procedure that is usually done on an outpatient basis. The basic steps of the surgery are as follows:
- Incision: A small incision is made in the eye, typically around 2.2 to 3.0 mm in size, to allow access to the cataract.
- Capsulorhexis: The surgeon creates a circular opening in the front portion of the lens capsule, a thin, elastic membrane that surrounds the natural lens.
- Phacoemulsification: Ultrasonic energy is used to break up and emulsify the cloudy lens, which is then suctioned out of the eye.
- IOL Implantation: The posterior chamber IOL is folded or rolled and inserted through the small incision. Once inside the eye, the IOL unfolds and is positioned behind the iris.
- Stabilization: The IOL is designed with haptics (small supporting arms) that help anchor it in the capsular bag, which is the remaining portion of the lens capsule. The haptics keep the IOL in place within the posterior chamber.
The posterior chamber IOL stays in place due to the support provided by the remaining lens capsule and the haptics of the IOL. The capsular bag acts as a natural barrier that holds the IOL securely in position. Over time, the tissues of the eye heal around the IOL, further stabilizing its position.
The design of the IOL and the surgical technique aim to ensure the lens remains centered and secure within the eye, allowing for clear vision and minimizing the risk of complications. After surgery, patients typically experience improved vision as the IOL replaces the cloudy natural lens, and the majority of individuals adapt well to the presence of the artificial lens in their eye. Regular follow-up appointments with the eye surgeon are important to monitor the healing process and address any concerns that may arise.
There are two ways that an intraocular lens can dislocate.
Defect in the supporting lens capsule: One is when there is a defect or tear in the capsular bag holding the lens and the lens slips out of the capsular bag. (That is shown in the accompanying image)
Loss of support for the lens capsule: Another way the IOL can dislocate is if it stays in the capsular bag and the entire capsular bag destabilizes and looses its support and shifts. The capsular bag is held in place by tiny fibers called lens zonules. They are about the consistency of a spider web. They can weaken over time and the lens and the lens capsule can shift out of position. This is called in-the-bag dislocation of an intraocular lens and is less common and a little more difficult to address surgically.
Posterior chamber intraocular lenses (IOLs) are exquisitely engineered to provide excellent vision when implanted into a stable capsule following extracapsular cataract extraction. If the lens capsule or the supporting lens zonules fail, and the IOL dislocates, vision usually deteriorates. Unfortunately, just as cars are not designed to be easily fixed after crashing, IOLs are not designed to be easily repositioned after dislocating.
If the intraocular lens is only slightly decentered, sometimes no therapy is necessary and sometimes a change in prescription glasses can compensate for the problem.
Interestingly, if the intraocular lens is totally out of position and settled in the vitreous of the eye, sometimes it can be left in the eye and a secondary lens can be placed without removing the lens. Both of these options avoid the risk of removing or manipulating the dislocated lens. The risk of surgery (like an eye surgery) include infection, bleeding, retinal detachment and corneal damage.
The most common procedure done for a dislocated intraocular lens is a lens exchange. The offending IOL is removed from the eye and a new lens is placed in the eye. If there is some capsule left in the eye that will support a larger IOL then a posterior chamber lens can be placed in the eye. If their is not capsular support adequate for a posterior chamber lens, then an anterior chamber IOL like the one in this photo can always be placed in front of the iris.
In addition, there are a few useful techniques where a posterior chamber IOL can be placed into an eye without capsular support. A posterior chamber IOL can be clipped to the iris, sutured to the iris, sutured to the sclera or the haptics of the IOL can be tunnelled into the sclera. All of these options are reasonable depending on the state of the cornea, iris, and capsule.
Our practice mostly offers treatment of dislocated intraocular lenses using a lens exchange. Our surgeons suture an Akreos AO60 posterior chamber intraocular lens in place at the same location, behind the iris, where a posterior chamber intraocular lens is normally placed. The Akreos AO60 posterior chamber intraocular lens has holes in the four haptics which can be used to suture fixate the lens. The procedure is safe and effective because it allows for four point fixation of the lens with an 8-0 gortex suture. The four point fixation reduces the chance of lens tilt which can happen with two point fixation. Also, the 8-0 gortex suture is very well tolerated.
This video was featured at the American Academy of Ophthlamology website in 2019 and shows fixation of a posterior chamber intraocular lens.
If the dislocated IOL is in good shape and free of surrounding capsular debris, it can be captured in the pupil and sutured to the iris. This technique is demonstrated in one of the video’s below. This technique only works well for dislocated IOLs that have haptics. There are other types of IOLs, like the crystalens IOL, that do not have haptics and cannot be sutured to the iris. The sutures holding the haptics of the IOL to the iris in the accompanying photograph are blue and can be seen where the arrows are pointing. The optic of the IOL is perfectly centered and not visible.
This patient had cataract surgery and some of the fragments from the surgery dropped into the vitreous. They are removed and then the intra-ocular lens, which is not stable, is sutured to the iris for stability.
When there is inadequate capsular support to allow simple repositioning of a dislocated IOL, sutures can be used to secure the IOL in the visual axis. The IOL can be sutured to the iris or the sclera. In cases of an in-the-bag dislocated IOL or a plate-haptic dislocated IOL, a transscleral 9-0 polypropylene fixation technique is preferable. The knots used to tie the transscleral sutures securing the IOL present a vexing problem. If they are covered with only conjunctiva and Tenon capsule, they usually erode through the covering. Once exposed, the knots irritate the eye and pose an increased risk of endophthalmitis. The technique presented in this article and the accompanying video obviates the need to make a scleral flap or tunnel by using the needle on the 9-0 polypropylene suture to bury the suture in the sclera. The knot can then be rotated into the eye through a preplaced 23-gauge sclerotomy.