Laser technology has revolutionized many fields. In ophthalmology, laser systems are used to photocoagulate, cut, remove, and stretch eye tissues. New types of lasers and applications continue to develop. This article will focus on the Nd: YAG laser and its role in treating ophthalmic disorders.
The first LASER was constructed in 1960 at Huges Research Laboratories. LASER stands for Light Amplification by Stimulated Emissions of Radiation. A laser contains material that releases photons. This process amplifies, so the emitted photons are in phase and produce monochromatic coherent high-intensity polarized light. The power modulates by altering the energy or time (P = E/t). Q-switching and mode-locking refer to increasing laser power methods using shutters that synchronize the light phase, compressing output in time.
The Nd: YAG laser is a unique solid-state laser that utilizes a neodymium-doped yttrium-aluminum-garnet crystal as the medium. It is pumped with a lamp or diode and commonly emits infrared light at 1064nm. It can be used in either a continuous or pulsed mode. Pulsing YAG lasers are typically Q-switched to achieve high-intensity pulses, which can be frequency doubled to emit the light at 532nm.
There are a variety of ophthalmic applications for YAG lasers. They are commonly used to treat posterior capsular opacification following cataract surgery. YAG laser can be used to create a peripheral iridotomy for patients with angle-closure glaucoma. Panretinal photocoagulation can be performed with frequency-doubled YAG lasers. A couple of other applications include the treatment of recurrent corneal erosions and vitreous floaters.
A more detailed description of some of these procedures follows:
Posterior capsulotomy: When a patient has a significant posterior capsular opacity or “secondary cataract,” a YAG laser is often used to open the posterior capsule centrally. Patients are pretreated with iopidine or Alphagan-P to prevent an IOP spike. Then under topical anesthesia, the laser treatment is performed with a slit-lamp delivery system using an appropriate contact lens (i.e., Abraham capsulotomy YAG lens) to stabilize the eye and focus the laser beam. The energy setting depends on the capsular opacification density, but the specific starting point is 1-2mJ, and the energy is titrating according to the tissue response. The YAG laser causes photodisruption with the shock wave traveling anteriorly. Therefore, most lasers have a focus offset control to allow the surgeon to place the laser beam posterior (up to 250 microns) to the HeNe beam focus point on the capsule. This process helps prevent the intraocular lens (IOL) from pitting. Most surgeons will also place the initial laser spots off-center to avoid inadvertently damaging the IOL near the visual axis.
Anterior capsulotomy: The YAG laser is also utilizing to cut the capsule in other conditions. Capsular block syndrome occurs when there is retained viscoelastic in the capsular bag behind the IOL. This process causes a myopic shift and is evident on slit-lamp examination as an apparent space between the posterior IOL surface and the posterior capsule. A YAG laser uses this to puncture the anterior capsule peripheral to the IOL optic to allow the trapped material to drain. Alternatively, a posterior capsulotomy can be created to achieve the same result. Anterior capsular contraction syndrome or capsular phimosis may occur with a small capsulorhexis. Making radial anterior capsulotomies with a YAG laser effectively treats this condition.
Peripheral iridotomy: Lasers have long replaced surgical iridectomies for the treatment of angle-closure glaucoma. This non-invasive laser procedure is performed prophylactically in eyes with narrow or occludable angles. The laser energy needed ranges from 4-10mJ depending on the iris thickness. This laser creates an iridotomy more efficiently than a green laser. A peripheral iridotomy could also be beneficial in pigmentary glaucoma.
Vitreolysis: YAG lasers are commonly used to treat aphakic and pseudophakic malignant glaucoma. YAG Laser vitreolysis can also be performed on strands of incarcerated vitreous in the anterior chamber that cause cystoid macular edema. Straightforward, thin vitreous wicks may be challenging to lyse, so it is best to pretreat with pilocarpine to induce miosis, stretch the incarcerated vitreous, and then use bursts 5-10mJ aimed at a pigmented area of the strand or near the wound. A change in the pupil shape back to round indicates successful vitreolysis.
ZEISS Visulas III
The ZEISS VISULAS YAG III laser brings together optical experience, technological excellence, and an understanding of clinical applications. It is supremely focused, yet gentle cutting action has earned the device its reputation as the “sensitive scalpel” amongst secondary cataract lasers.
The high-precision Super-Gaussian beam of the VISULAS YAG III focuses on the optimum amount of energy onto the point of treatment. This process allows successful disruption to take place at just 2.5 mJ in air. In turn, this will enable you to offer precise treatment to your patients using a minimal amount of laser energy. The pulse frequency of 2.5 Hz also facilitates a fast workflow and short treatment times.
The Fine adjustment of energy Offering twenty-two levels of energy attenuation, the VISULAS YAG III provides ample flexibility for various treatment techniques. The subtle gradations at the low end of the output range allow optimum laser energy regulation for your patients’ minimally invasive treatment.
The variable focus shift sets the focal point of the aiming beam precisely before, behind, or directly at the laser’s focal point. Thanks to this safety feature, damage to the tissue and intraocular lens is now also a thing of the past. This process means greater comfort for your patients.
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