When Charles Kelman, MD1 first introduced the concept of ultrasound phacoemulsification, few could envision the small-incision surgery revolution that would then begin. With greater refinements, phacoemulsification has become the procedure of choice among cataract surgeons.2 With phacoemulsification, however, there are issues of safety related to the release of energy at the tip of the probe. The heat that the phacoemulsification probe tip generates requires a cooling irrigation sleeve to reduce the risk of corneal burn and/or wound distortion, and necessitates a 2.2 to 3.2-mm incision size.
On the other hand, the Dodick Photolysis™ System (A.R.C. Laser Corp., Salt Lake City, UT), currently the only laser approved for cataract extraction by the FDA, transfers laser energy from the laser source to a laser probe via a 300-µm quartz-clad fiber optic. The laser probe produces no significant heat3 and requires no cooling sleeve. This offers two clear advantages: it eliminates the risk of corneal burn, and it allows for the separation of the irrigation port from the emulsifying needle, which permits a reduced diameter of the handpieces, and consequently smaller wound sizes (Figure 1).
The Dodick Photolysis™ System uses a Venturi system that generates aspiration in a range of 0 to 650 mm Hg. The infusion system ranges from 0 to 200 mm Hg.The laser output uses a pulse rate of 1 to 20 Hz, with an output of 8 or 10 mJ per pulse. Current probes have an external diameter of 1.2 mm and an internal diameter of 0.75 mm, and smaller probe designs (0.9 mm external diameter) are presently being investigated. Current techniques involve the creation of two 1.4-mm incisions, for the irrigation probe and the combination laser/aspiration probe. The handpieces are disposable, and may be used for the removal of cortex.
The photolysis unit includes a Venturi phacoemulsification unit that uses a 2.75-mm phacoemulsification needle and conventional irrigation/aspiration handpieces for cortical removal. It also contains a high-speed vitrectomy unit that can use a one-piece or split vitrector.
In a multicenter study, Kanellopoulos et al4 studied 1,000 consecutive photolysis patients. The mean visual acuity improvement was from 20/70.2 to 20/24.4, and the mean energy used was 5.65 J per case. The average photolysis time was comparable to phacoemulsification times for the cataracts from 1-2+ in density, but the average time for 3+ lenses was 9.8 minutes. The investigators concluded that photolysis was a safe and effective alternative to phacoemulsification in softer cataracts, with a follow-up time of 2 years.
In a separate clinical trial, Huetz and Eckhardt5 reported on 100 patients with photolysis with a 6-month follow-up. There was no significant difference in pachymetry in groups 1 and 2 (LOCS III system) pre- and postoperatively, however, group 3 experienced an average increase in pachymetry to 1.84% on postoperative day 2. Of note, at 6 months, there was no significant difference in pachymetry from preoperative values in all three of the groups.SURGICAL TECHNIQUES
The classic technique involves the creation of a ?bowl? prior to the removal of the lens from the capsular bag. Two 1.4-mm incisions are created in the clear cornea. After the completion of a capsulorhexis, hydrodissection is performed. The irrigation handpiece and the laser/aspiration handpiece are placed on the cataract. The aspiration/laser handpiece ablates pieces of the cataract centrally, and once the central plate of the cataract has been ablated, the residual shell is aspirated into the anterior chamber. The major limitation of this technique is that it is slightly slower than other techniques, and is only effective in softer nuclei.
In the Dodick technique, the lens is prechopped into two hemispheres in a horizontal chopping technique. One or both of the residual hemispheres is then rechopped into quarters. The quadrants are ablated using the separate aspiration-laser and irrigation handpieces. Advantages of this technique are that less energy is required (this is also true for prechopping using phacoemulsification), and a smaller capsulorhexis may be used. Disadvantages involve the learning curve necessary for mastering this skill.
The Wehener technique necessitates the creation of a large capsulorhexis for the entire nucleus to be lifted into the anterior chamber using high aspiration, and the irrigation handpiece is placed beneath the nucleus. The nucleus is then brought down and ?back-cracked? over the irrigation handpiece. A specialized irrigation handpiece, called a Wehener Spoon, which has a pointed end angled upward toward the nucleus can be utilized. The advantage of this technique is the potential protection of the posterior capsule as irrigation is directed toward it. Potential disadvantages of this technique include the difficulty in passing the Wehener Spoon into the eye, and the need for a large capsulorhexis.
Just as phacoemulsification requires the occasional conversion to conventional extracapsular cataract extraction techniques, photolysis may require conversion to phacoemulsification. How often this is required depends on experience with appropriate patient selection, experience and expertise of the surgeon, and factors endogenous to the eye. Conversion to phacoemulsification does not appear to pose any greater risks than the initial use of phacoemulsification without conversion. One of the photolysis incisions is enlarged with a 2.75-mm blade. Phacoemulsification is then performed in the conventional fashion.
IOLs that can be inserted through a 1.4-mm incision are currently being investigated and have been successfully utilized in Europe. Kanellopoulos et al4 reported implanting a dehydrated prefolded Acritec™ acrylic lens in three cases in which they used the Dodick Photolysis™ System. The dehydrated lens is prefolded to an external diameter of 1.2 to 1.3 mm and implanted through the original photolysis incision. The lens fully unfolds within the capsular bag within 30 minutes postoperatively. Of note, the cases were completed through incisions no larger than 1.3 mm.
Another lens implanted in Europe is the ThinOptX® (Abingdon, VA) Ultra Thin™ Lens. The lens is designed to use a series of refractive rings concentric to the optical center. These rings focus on one focal point, as distinct from a Fresnel prism (prismatic lens). This plate lens design passes through a 1-mm incision. The lens is folded in half and subsequently rolled and placed into the capsular bag. Warm balanced saline solution is used during lens folding to speed unfurling within the capsular bag.
TO ADOPT OR NOT TO ADOPT
The question of whether to be an early adopter of technology, or to wait until further refinements have been made, will largely depend on the style of the surgeon. Early adopters of technology have the advantage of developing familiarity with machines, fluidics, and techniques before they become expected knowledge of the average surgeon, and can sooner meet the ever-increasing demands of patients for the latest technologies. Disadvantages of adopting techniques early in the developmental phase involve using technology that is not yet fully perfected.
Photolysis is currently restricted in its treatment of dense cataracts, similar to the early limitations of phacoemulsification. Given the rapid advances being made in technology, it is likely that these will soon be overcome. Photolysis is an important development in the march toward endocapsular surgery, which may preserve accommodation as well as eliminate posterior capsular opacities, and render current technology obsolete. nIman Ali Pahlavi, MD, is from the Manhattan Eye, Ear & Throat Hospital. She may be reached at (212) 838-9200; Imanpahlavi@netzero.net. Dr. Pahlavi does not hold a financial interest in any of the materials presented herein.
Jack M. Dodick, MD, is Chairman of the Manhattan Eye, Ear & Throat Hospital. He may be reached at (212) 838-9200; email@example.com. Dr. Dodick is the inventor and patent holder for The Dodick Photolysis™ System. Portions of material extracted from presentation given at the AAO meeting in New Orleans, LA.
1. Kelman CD: Phaco-emulsification and aspiration: A new technique of cataract removal, a preliminary report. Am J Ophthalmol 64:23-25, 1967
2. Leaming DV: Practice styles and preferences of ASCRS members—1999 survey. J Cataract Refract Surg 26:913-921, 2000
3. Alzner E, Grabner G: Dodick laser phacolysis: Thermal effects. J Cataract Refract Surg 25:800-803, 1999
4. Kanellopoulos AJ, et al: Laser cataract surgery: A prospective clinical evaluation of 1000 consecutive laser procedures using the Dodick Photolysis neodymium:YAG system. Ophthalmology 108:649-654, 2001
5. Huetz WW, Eckhardt HB: Prospective clinical study with photolysis using the Dodick-ARC laser system for cataract surgery (personal correspondence)