Lens Replacement Surgery for Angle Closure
Chat Highlights – January 2, 2013
Guest Speaker – Dr. Michael Pro
Lorraine Miller, Editor, Chat Topic Researcher
Moderator: Good evening and Happy New Year! Tonight we will be discussing “Lens Replacement Surgery for Angle Closure.” We would like to welcome Dr. Michael Pro, our medical expert.
P: Would you please define angle closure glaucoma for those attending this evening?
Dr. Pro: Angle closure glaucoma is defined by the presence of a narrow anterior chamber angle. The angle is the space between the cornea and the iris and is where the aqueous fluid leaves the eye. In most individuals this space is open and there is no obvious structural reason for the elevated IOP that is a feature of glaucoma. However, in angle closure, the drainage angle is narrow or even totally closed. This can obstruct the outflow of aqueous fluid. In extreme cases, an angle closure attack can occur where the IOP is extremely high. An angle closure attack is a painful medical emergency.
P: What is lens replacement surgery?
Dr. Pro: Lens replacement surgery is more commonly referred to as cataract surgery. In almost all cases, the cloudy lens or cataract is replaced by a clear artificial intraocular lens (IOL).
P: When is cataract surgery offered to a patient with angle closure glaucoma?
Dr. Pro: The timing of cataract surgery in a glaucoma patient depends on the status of glaucoma disease control. In a patient with medically well-controlled glaucoma, the timing of cataract surgery is often the same as any other patient with a cataract. The cataract surgery is undertaken when the cataract is visually significant to the patient. In general vision, this could be 20/40 or worse but cataract surgery may be performed earlier if the patient is symptomatic with glare or some other problem.
With individuals who have angle closure glaucoma, there is a growing body of evidence that earlier cataract surgery may help to open the anterior chamber angle and may benefit long-term glaucoma control. This has been studied more extensively in East Asian countries where angle closure glaucoma is more common.
In an ACG patient with uncontrolled glaucoma, the cataract surgery may need to occur earlier. The patient may have visual field progression and optic nerve changes and need a trabeculectomy or another glaucoma filtering surgery and the cataract would be done at the same time.
P: Are there any other surgical procedures that can be used instead of the lens replacement surgery where the results are just as predictable?
Dr. Pro: General cataract surgery is not a predictable means to control the IOP in open-angle glaucoma patients. However, there is a recent study from Hong Kong that compared cataract surgery to a trabeculectomy for controlling the IOP of patients with ACG. The theory is that removing the cataract and replacing it with an IOL opens the angle and improves aqueous outflow. The authors concluded that both cataract surgery and trabeculectomy controlled IOP. Patients needed more glaucoma drops if they had cataract surgery alone but more complications were seen in the trabeculectomy group.
P: Is the lens replaced even if there is no cataract, or is there always a cataract present?
Dr. Pro: There are times when a clear crystalline lens is removed and replaced with an IOL. This is done in some cases of angle closure and has been proposed, more in East Asian countries, as a treatment for an acute angle closure attack. The premise is that removing the lens opens the angle. The natural lens is relatively thick and the IOL is very thin taking up less space in the front of the eye. Early cataract surgery may help prevent the gradual development of scar tissue adhesions between the iris and the angle seen in individuals with ACG. We think this is due to the irritative effect of the iris against the sclera in the crowded angle.
It certainly makes a lot of sense scientifically, but clear lens exchange is not as straightforward in practice. Surgery is proposed on an individual with no visual complaints. Even though cataract surgery is very successful, it is not without some risks, however uncommon.
P: Are angle closure patients more prone to hyphema and shallower anterior chambers following clear lens extraction compared to other glaucoma subtypes?
Dr. Pro: I am not aware of them being more prone to hyphemas (bleeding in the front portion of the eye). They may be more prone to an attack of malignant glaucoma or aqueous misdirection after surgery. This is a very rare situation where the lens and iris are pushed nearly up against the cornea and the IOP is often high.
P: How common is this for patients with aqueous misdirection or malignant glaucoma attacks? In this case, is it common to perform a vitrectomy?
Dr. Pro: I see one or two per year at most. So, it is rare! It is treated stepwise. First, try dilating drops. The drops work some of the time to break the attack. Next, a laser may be used to break the attack. If this doesn’t work, then a vitrectomy is would follow.
P: If the lenses are removed and the angle opened, is the glaucoma said to be “cured?”
Dr. Pro: We are reluctant to say “cured” when it comes to glaucoma. Glaucoma may be defined as damage to the optic nerve partially due to IOP that is too high for a particular eye. The idea of any glaucoma therapy is to prevent more damage. There are individuals with narrow angles and completely healthy nerves. For these individuals, opening the angle with a laser iridotomy or with cataract surgery may prevent the future development of higher IOP due to scar tissue in the angle and subsequent glaucoma.
P: Is the selection of an IOL different for those who suffer from angle closure glaucoma?
Dr. Pro: No, the selection is not different. A person with a narrow angle is farsighted and may have a slightly shorter eye from back to front. The power of the IOL is different from one eye to the next and farsighted eyes tend to have IOLs with higher dioptric power. However, the same IOL models are used in any eyes.
P: Can a lens replacement cause angle closure?
Dr. Pro: This is called phakic angle closure and is rare. It is seen more often when the replacement IOL is located in front of the iris instead of the much more common and physiologic location behind the iris. Anterior chamber IOLs (ACIOL) are less common today. Attacks are seen in patients with intraocular inflammation.
Moderator: Thank you, Dr. Pro!
Dr. Pro: Thanks and good night!