YAG Laser Cataract Surgery

Cataract surgery has been performed for over two millennia, but advances in technology have transformed the fundamental procedure only over the past 40 years. The use of ultrasound vibration to remove cataracts through a small incision was pioneered by Charles Kelman in the 1960s, and the technique has been developed to become the standard procedure for most cataract extractions in developed countries. The Kelman phacoemulsification procedure has also become the main framework upon which innovations in cataract surgery are built. Such innovations are driven by the need for less trauma during surgery and faster visual recovery after surgery. Surgeons have strived to reduce incision size, heat, intraocular turbulence and fluid level in order to achieve these objectives. Ultrasonic phacoemulsification probe tips tend to create relatively high levels of heat within the eye, resulting in the possibility of injury to the cornea such as corneal burns and endothelial damage. Technological advances over the past decade have reduced the effective energy liberated by the probe, chiefly through using ultrasound energy more efficiently.

Perhaps the most promising front in atraumatic phacoemulsification surgery is the application of the yttrium-aluminum-garnet (YAG) laser towards emulsifying the cataract. The first laser procedure for cataract surgery was reported in 1975 by Krasnov, who used a technique called “laser phacopuncture” to make microperforations on the anterior capsule. These pores then allowed the release of lens material into the anterior chamber, which would be theoretically resorbed over time. Krasnov’s Q-switched ruby laser technique had limited application, since the micropores would only allow the release of very soft cataracts. Furthermore, patients had to be maintained on dilator drops for extended periods to prevent the puncture sites from closing, and steroid drops to reduce anterior uveitis that inevitably occurred from the released cataract in the anterior chamber. Additional experiments with laser cataract surgery occurred with excimer lasers, most notably the 308 nm laser. The xenon chloride 308 nm laser was introduced in the late 1980s, but was abandoned for cataract surgery due to concerns over retinal toxicity. The neodymium:yttrium-aluminum-garnet (Nd:YAG) laser was used successfully to perform posterior capsulotomy in 1980. The YAG laser gained wide acceptance among surgeons as an excellent method of treating posterior capsular opacification after cataract surgery. The popularity of the Nd:YAG laser in posterior capsulotomies motivated researchers to explore how the YAG laser could be used to treat cataracts. A technique called laser photofragmentation, which uses the Nd:YAG laser to soften the nucleus before phacoemulsification, was explored in the mid-1980s. This procedure did reduce phacoemulsification power and time, but also increased the risk of capsular perforations.

The YAG laser has the potential to dramatically reduce the energy required to perform cataract surgery. Two types of YAG lasers are being developed for cataract surgery: the neodymium:YAG (Nd:YAG) and Erbium:YAG (Er:YAG) laser. The pulsed Q-switched Nd:YAG laser, which emits at 1064 nm, does not produce direct laser light at the tip; instead, it generates shock waves through a titanium block at the tip to photolyse the cataract. This technology produces negligible heat at the tip, and therefore does not require a cooling sleeve to avoid corneal burns. Consequently, incisions as small as 1.25 mm can be used to perform the procedure. Laser emulsification is relatively short for most cataracts, but can take over 10 minutes for nuclear sclerosis over 3+. Another Nd:YAG laser, which uses photoacoustic ablation under aspiration, delivers energy through a ski-shaped distal tip to create a “photon trap”. This technology is most useful for softer nuclear sclerosis. The Er:YAG laser, which emits at 2940 nm, relies on its infrared spectrum wavelength in cataract surgery. At this wavelength, the laser produces cavitation bubbles that collapse slowly in the cataract and very quickly in water. This leads to propagated energy within the lens, allowing the laser to emulsify the material efficiently without producing thermal energy. The laser can be used with a prechopper to reduce the operating time.

Each of these YAG laser technologies can be coupled with standard I/A pumps to allow a lenticular emulsification with little or no thermal energy. The technologies open up the possibility of performing cataract surgery through very small (<2 mm) incision sizes, intraocular lenses to fit through such small openings are being developed rapidly.