Nd-YAG Laser Capsulotomy

Background

Neodymium-doped yttrium aluminum garnet (Nd:YAG) laser capsulotomy is a relatively noninvasive procedure that is used in the treatment of posterior capsular opacification. Posterior capsular opacification is a common long-term complication of cataract surgery that causes decreased vision, glare, and other symptoms similar to that of the original cataract. ^[1] Posterior capsular opacification is caused by a proliferation of lens epithelial cells, which causes fibrotic changes and wrinkling of the posterior capsule. Its reported frequency ranges from 8.7% to 33.4%. ^{[2, 3, 4, 5]}

Laser capsulotomy uses a quick-pulsed Nd:YAG laser to apply a series of focal ablations in the posterior capsule and create a small circular opening in the visual axis. Yttrium aluminum garnet (YAG) capsulotomies were developed in the early 1980s by Drs. Aron-Rosa and Fankhauser. Aron-Rosa had a strong background in physics prior to becoming an ophthalmologist and an especially keen interest in the early ruby lasers of the time. She found that the pulses were too slow for her intention, which was to determine a laser beam wavelength that would not disrupt the integrity or temperature of surrounding tissue within 100 μm of the target.

By multiplying the Nd:YAG frequency, Dr. Aron-Rosa was able to use the laser in various wavelengths. She applied for a patent in 1978 and began her clinical trials in October of that year. Over the next 4 years, she performed the procedure in 5000 eyes. ^[6] In November 1980, Fankhauser performed his first YAG capsulotomy. ^[7] The procedure caught on quickly because the alternative was surgical dissection of the posterior capsule, which is a more inherently invasive procedure. With the older intraocular lenses, opacification rates could be as high as 50%. ^[8] As the intraocular lens technology has improved, the rates of opacification have decreased greatly.

Indications

Indications for Nd:YAG laser capsulotomy include the following:

• Interference with daily activities

• Decreased vision (patients with multifocal intraocular lenses may be particularly sensitive to even small posterior capsular changes)

• Increased glare

• Difficulty visualizing the fundus

• Lens tilt and Z syndrome associated with hinged accommodating lenses such as the Crystalens and Trulign toric lens (lens tilt occurs when one haptic is planar and the other haptic is vaulted anteriorly or posteriorly; Z syndrome occurs when one haptic is vaulted anteriorly and the other is vaulted posteriorly)

In cases of a small anterior capsulorrhexis, capsular phimosis or capsular contraction can occur. This excessive scarring anterior to the intraocular lens can compromise vision. It can be alleviated by radial anterior capsulotomies, which can be achieved with the Nd:YAG laser. ^[9]

Contraindications

Relative contraindications for Nd:YAG capsulotomies include the following:

• Corneal scarring or edema that prevents a clear view during the procedure

• Placement of a glass intraocular lens during cataract surgery

• Presence of iritis in the eye

• Macular edema in the retina

Use caution in the following cases:

• Patients with a history of retinal tears or detachments ^[10]

• Patients in the immediate postoperative period because the intraocular lens may not be adequately scarred into place

• Patients with glaucoma, who may have an intraocular pressure spike from the inflammation or postoperative steroid response ^[11]

Equipment

An Abraham YAG capsulotomy lens is used in conjunction with a coupling agent, such as 2% or 2.5% hydroxypropyl methylcellulose, to form a seal on the eye. In addition to helping keep the eye open, the lens has a 10.0-mm helium-neon YAG-coated plano-convex 1.8× magnification button positioned at the center of the lens, which focuses the beam spot size on the posterior capsule.

Patient Preparation

Anesthesia

Topical anesthesia can be used to perform Nd:YAG capsulotomies without any significant discomfort for the patient.

Positioning

Nd:YAG capsulotomy is performed at a slit lamp equipped with a YAG laser, while the patient is in a seated position. ^[12]

Monitoring & Follow-up

Patients are usually put on topical steroids for inflammation at the discretion of the surgeon.

Patients are usually brought back at 1 week postoperatively for a manifest refraction and to assess the intraocular pressure and inflammation. A dilated fundus examination can be performed to rule out macular edema or tears in symptomatic patients, but it is not necessary. A postoperative examination after 1 month can be performed, but that is also optional.

Retreatment is not necessary unless the YAG did not ablate the posterior capsule fully or if it was cut short because of excessive energy.

Complications

Complications may include the following:

• Transient intraocular pressure elevation

• Iritis

• Retinal tears and detachments

• Macular edema

• Corneal edema

• Intraocular lens dislocation into the vitreous

• Pitting of the intraocular lens

The incidence of intraocular pressure elevations are significantly reduced when patients are pretreated with apraclonidine. Intraocular pressure can be checked 30-60 minutes postoperatively, although that is surgeon dependent.

Iritis can be present after the capsulotomy, but it is usually self-limited. It can be treated with a weeklong course of topical steroids (1% prednisone acetate or 0.5% loteprednol, 4 times daily).

Patients are usually pretreated with dilating drops, such as tropicamide 1.0%, phenylephrine 2.5%, or cyclopentolate 1-2%, as the posterior capsular opacity needs to be visualized through a dilated pupil. To prevent a transient postoperative intraocular pressure spike, a drop of apraclonidine 0.5% can also be given.

The laser should be set somewhere from 1-3 mJ and can be Q-switched, mode locked, or both. A Q-switched laser produces a series of single pulses that each last 12-20 nanoseconds, whereas a mode-locked laser produces a train of pulses that each last 25-30 picoseconds. These settings help deliver higher power.

Because the Nd:YAG laser is actually invisible, a helium-neon laser is actually used as a focusing device. ^[13] The laser can be focused slightly posterior to the lens to avoid pitting of the lens. Silicone lenses have been found to be more easily damaged than acrylic lenses. Polymethylmethacrylate lenses have been found to be the most resilient.

Methods of laser treatment are surgeon dependent and may depend on the density of the opacity. A cross-pattern with both axes beginning in the periphery has been advocated by many physicians to decrease the risk of central pitting. ^[14] A circular laser can be applied afterwards. Other physicians recommend avoiding a circular laser in favor of firing on fixed stress lines. The capsule should reflect out of the visual axis on its own. ^[15] Another method is to make a 3-mm inverted U-shape, such that the capsule reflects inferiorly. It is claimed that the flap stays out of the visual axis and cuts down on postoperative floaters. ^[16]

Small capsulotomies (2-3 mm) have been found to be equally as effective as large capsulotomies (5-6 mm), although larger capsulotomies may be more helpful for those with symptomatic glare. ^[17]

A host of methods to treat lens tilt and Z syndrome with Nd:YAG laser have been postulated. Treatment typically centers on trying to relieve tension behind the anteriorly vaulted haptic by performing a small oval capsulotomy between the hinge and the insertion of the hinge loops, taking care to lyse any fibrotic bands that are present. It is important to avoid extending the capsulotomy past the edge of the optic to avoid anterior migration of the vitreous. If this is insufficient, a small noncontiguous central capsulotomy can be done. If this is also insufficient, a small oval capsulotomy behind the posteriorly vaulted haptic can also be performed. ^[18]