3rd April 2009
Lens Extraction for Glaucoma
One of the most challenging clinical problems we face is acute primary angle closure. Patients are often in pain and difficult to examine, but they require swift action to prevent permanent vision loss. Once the emergency is under control, plans are considered for longer term treatment. And evidence is mounting that lens extraction may offer greater therapeutic benefits than laser peripheral iridotomy.
The immediate medical treatment for an angle closure attack is well-known to all of us and has not changed for many years—administration of a combination of systemic and topical aqueous suppressants to reduce the intraocular pressure below 40 mm Hg. At this level, pilocarpine can break the attack by pulling the peripheral iris away from its contact with the trabecular meshwork.
Once the attack is controlled, the classical treatment has been laser peripheral iridectomy (LPI), a treatment that has long been considered the cure. However, despite successful LPI, many patients continue to have persistent difficulties with ocular hypertension suggesting the development of combined mechanism glaucoma.
Lens Extraction Option
A recent study published in the journal Ophthalmology strongly suggests that lens extraction and IOL implantation can significantly reduce the incidence of future ocular hypertension. Of course, this option best serves angle closure patients with cataracts—even if they are early in formation.
Sixty-two patients with recent medically controlled angle closure and early to moderate cataracts (VA 20/30 or worse) were divided into 2 groups:
- Half were treated with LPI
- Half underwent lens extraction and IOL implantation
After subjects were weaned off of IOP lowering meds, pressures were measured at regular intervals for 18 months:
- 46.7% of the LPI group had IOP greater than 21 mm Hg
- 3.3% of the lens extraction group had IOP greater than 21 mm Hg
Why the difference? Additional study observations provide interesting clues:
- The extent of peripheral anterior synechia, the persistent, often permanent adhesion of the peripheral iris with the TM, averaged:
1. 228.6 degrees in the LPI group
2. 101.3 degrees in the lens extraction group
- The mean Schaffer gonioscopy angle grading for the 4 quadrants was:
1. 0.73 for the LPI group (only the anterior TM was visible)
2. 2.10 for the lens extraction group (the entire TM was visible)
Lens extraction provides more drainage area than LPI.
- LPI relieves relative pupillary block and iris bombe so that in most cases the angle opens enough to expose an adequate amount of TM to lower and then maintain the IOP at more normal levels.
- LPI does not lessen the steep iris approach into the angle caused by the thickened crystalline lens.
- After LPI, the peripheral iris remains close to the TM resulting in continued risk of iris-corneal adhesions and a less than normal area of available functioning TM.
- Lens extraction deepens the central anterior chamber depth so that the angle is wider and therefore more open than with LPI, increasing the amount of available functioning TM.
Role of the Lens
Reviewing the role of the lens in angle closure helps explain what researchers observed in this study. Certain eyes, most often hyperopic eyes with shorter axial lengths, have a more anteriorly positioned iris root. With aging and cataract formation, the lens naturally thickens. In fact, an often overlooked risk factor for angle closure is a shallowing of the central anterior chamber.
Normal young eye
Lens thickened by cataract pushes iris forward
IOL allows iris to return to normal position
Consensus at PCLI
This study supports the consensus among PCLI surgeons that lens extraction is the treatment of choice for patients with medically stabilized acute primary angle closure and cataracts. It may even be our preferred treatment for patients with mild to moderate cataracts and narrow angles.
At this point, insurance will probably not cover lens exchange surgery without the current visual criteria for cataract treatment being met. However, an argument could be made that lens exchange is not only justifiable but preferable—even in well-seeing eyes. The thickened crystalline lens is a primary cause of angle closure and its removal may significantly reduce the incidence of vision loss from future combined mechanism glaucoma.
If you have questions or would like more information on this topic, or the management of angle closure in general, feel free to contact me or any of our optometric physicians.