Anterior chamber depth can play significant role in phaco
Careful evaluation and management can result in success even if the chamber is shallow or deep.
One of the challenges of phacoemulsification surgery is operating within the tight confines of the anterior segment of the eye. The volume of this working space is less than 1 cm3, with delicate ocular structures just millimeters away. The corneal endothelium and posterior lens capsule are subject to irreparable damage should the fluidic balance induce anterior chamber instability.
Before surgery, the anterior chamber should be carefully examined using the slit lamp microscope as well as measured via biometry. A shallow anterior chamber can be seen in physiologically normal but small eyes with short axial lengths as well as even smaller nanophthalmic eyes. In these eyes, the lens calculations are best done with the Holladay 2 formula due to the anterior effective lens position.
A shallow anterior chamber can be the result of a pathologic process within the eye, such as glaucoma. In narrow angle glaucoma, the anterior chamber is shallow due to the configuration of the anatomic angle. As cataracts develop, the anteroposterior dimension of the human lens can increase, further crowding the angle. In these eyes, cataract surgery not only improves vision, but it can also help to treat the glaucoma by opening the angle of the eye.
Pseudoexfoliation is a disease process in which the zonules that support the lens can become loose, allowing the lens-iris diaphragm to push the iris forward and induce a shallow anterior chamber. Biometry of a pseudoexfoliation eye that shows a normal to long axial length but a short anterior chamber depth is a sign that the zonules will be particularly weak during cataract surgery.
Images: Devgan U
A very deep anterior chamber is most often seen in large myopic eyes with long axial lengths. Although it can provide additional room during phacoemulsification surgery, these eyes tend to have more elastic scleral tissue and are prone to an overly deep anterior chamber during surgery. An increase in anterior chamber depth is also seen in cases of trauma in which ocular structures such as the zonules, lens or angle of the eye can become damaged. Identification of the extent of ocular trauma ahead of time is helpful in formulating an appropriate surgical plan.
With a shallow anterior chamber, performing a capsulorrhexis at the beginning of the cataract surgery is difficult due to poor maneuverability and lack of flattening of the anterior lens capsule. In most situations, this can be addressed by injecting viscoelastics at the time of surgery. Cohesive viscoelastics do a better job of creating and maintaining space. In that regard, strongly cohesive OVDs such as Healon GV (1.4% sodium hyaluronate, Abbott Medical Optics) or viscoadaptive products such as Healon5 (2.3% sodium hyaluronate, AMO) tend to be the most effective choices. In rare cases, if the anterior segment remains excessively shallow, a limited pars plana anterior vitrectomy can be done to remove volume from the vitreous cavity. This allows the anterior chamber to be further deepened during surgery but may pose additional risks to the retina. Therefore, this technique should be used cautiously. During phacoemulsification, the bottle height can be raised in order to increase the infusion pressure into the anterior chamber, thereby deepening it.
In large myopic eyes with excessively deep anterior chambers, the bottle height can be lowered during surgery. However, the usual cause of the excessively deep anterior chamber in these eyes is a reverse pupillary block. The iris and anterior lens capsule form a tight seal that prevents infusion fluid from equalizing with the posterior chamber. This can be resolved by breaking the reverse pupillary block via lifting the iris with the chopper or second instrument. For prolonged cases, a single nasal iris hook can be placed in order to avoid an excessively deep anterior chamber for the entire surgery.
While the working space within the anterior segment of the eye is small, careful evaluation and management of surgical parameters can allow us to modulate its size and operate safely.
- Uday Devgan, MD, FACS, is in private practice at Devgan Eye in Los Angeles, chief of ophthalmology at Olive View UCLA Medical Center and an associate clinical professor at the UCLA School of Medicine. Dr. Devgan can be reached at 11600 Wilshire Blvd., Suite 200, Los Angeles, CA 90025; 800-337-1969; fax: 310-388-3028; e-mail: email@example.com; Web site: www.devganeye.com. Dr. Devgan is a consultant to Abbott Medical Optics.