Presbyopia is a unique landmark—as one of the greatest certainties of life, it is a progressive sign of aging. Everybody who lives beyond 45 years is bound to experience this process. In some cases, the effects of presbyopia begin even sooner. We have understood presbyopia for quite some time; however, more recently, there has been a push to discover technologies that cure presbyopia rather than mask its effects. Why must we now tackle this challenge?
Up until 10 years ago, people tended to accept presbyopia as a part of life and were content wearing spectacles to treat the accommodative error. With the advent of LASIK, and then premium refractive IOLs, however, patients with presbyopia started to demand more correction. This is coupled with the extra needs of the baby boomer in our modern world, where computers, cell phones, and PDAs are commonplace and the average patient continues to enjoy an active lifestyle.
But is cosmesis the only reason for finding a solution to presbyopia? No. There is a great deal of visual incapacity caused by this aging change. No one likes the thought of losing near vision, contrast sensitivity, or the ability to accommodate.
TACKLING THE PRESBYOPIC PATIENT
In our practice, we treat a lot of parents whose children enjoyed a positive experience with refractive surgery. These jealous seniors also want to function without their glasses. Because they belong to a productive and financially independent group, parents constitute a significant group of potential patients.
One of the first things that should occur is counseling the patient: Make sure each patient understands that presbyopia is progressive. Relay that you may not be able to treat his future predicament given current technology. Explain the possibility that a repeat procedure may eventually be required. Emphasize that there is always some give-and-take in these procedures.
Once the patient understands, you may then move on to the decision-making process. There are several broad categories of presbyopia correction: spectacles and contact lenses; scleral, corneal, and crystalline-lens based surgeries; and presbyopic lens exchange. Within these categories, the corneal options include monovision LASIK, presby-LASIK, and conductive keratoplasty.
We offer four treatment options to our patients: (1) laser sclerostomy, (2) presby-LASIK, (3) conductive keratoplasty, or (4) IOL implantation with a pseudoaccommodating, monofocal, or accommodating IOL, in this order. When a monofocal IOL is used, monovision is the goal. We have a treatment chart, based on the patient's age and refraction, that guides our suggestions for treatment. In this article, I will share our experience with two corneal-based procedures, one of which is laser-based and the other of which is radio-frequency—based.
The idea of presby-LASIK originated from the multifocal design of the Array IOL (Advanced Medical Optics, Inc., Santa Ana, California). We use the EC-5000CX CXIII Excimer Laser System platform (Nidek, Inc., Gamagori, Japan) to create the multifocal cornea. The concept is to use the central zone for predominantly far vision and the peripheral zones for near, which essentially consists of three to four stages of treatment with varying zones. To begin, the cornea is ablated for a hyperopic treatment in a large zone (6 and 9.5 mm). Some of the hyperopic effect is nullified by the myopic ablation, performed first in the 3- to 4-mm optical zone and then again at the 4- to 5-mm zone. This creates the multifocality and allows the person to read and also see for distance.
Usually we offer this modality to patients between the ages of 40 and 60 years and with 2.00 to 4.00 D of hyperopia. Patients are typically satisfied with the outcome; however, there is some fluctuation of vision, and the patient may lose some lines of distance vision.
Conductive keratoplasty (CK) works on the principle of thermokeratoplasty. We typically offer this treatment to our patients between the ages of 45 and 55 years who are either plano presbyopes or mild hyperopes (up to 1.00 D).
CK is a laserless procedure involving the controlled intrastromal delivery of 350 kHz radio frequency energy into the corneal stroma by means of a contact probe tip. The energy is delivered at eight to 32 treatment points; energy release is controlled with a foot pedal. The energy passes from the generator to the probe tip, into the corneal stroma, and returns via the lid speculum. Corneal tissue conducts the radio frequency energy.
Thermal power and duration is optimal for collagen shrinkage (default setting of constant power for 0.6 seconds). The treatment is given in the mid-periphery in a circular pattern of eight spots that result in a band of collagen shrinkage. This band causes a purse-string effect and slightly balloons the apical cornea, providing more refractive power, and thus, improving the ability to read.
CK is performed with the ViewPoint CK System (Refractec, Inc., Irvine, California; Figure 1A). The keratoplasty tip (Figure 1B) is inserted into the cornea at premarked optical zones. The circular mark is on the 7-mm optical zone; an inner hatch mark lies on the 6-mm optical zone, and an outer hatch lies on the 8-mm optical zone (Figure 2).
Radio frequency energy application results in heat because tissue resistance to the current creates heat. The tissue is heated from the bottom to provide deep coagulation at the treatment spot.
During treatment application, the thermal effect proceeds from the point of the probe and up the shaft as it finds the path of least resistance. Thus, the tissue is exposed to the same temperature at the tip of the probe (deep stroma) as it is on the surface. The result is a narrow cylindrical lesion approximately 80% of corneal depth.
In contrast, the Hyperion noncontact LTK technique (lamellar thermal keratoplasty; Sunrise Technologies, Freemont, California) generates the greatest amount of heat at the surface of the cornea. The Ho:YAG laser light energy is highly absorbed in water and is attenuated as it passes through the cornea. The heat therefore diffuses radially and axially into the corneal tissue. The result is corneal denaturation decreasing from top to bottom, forming a cone-shaped zone of denatured collagen. A circle of cylindrical treatment spots applied in the mid-peripheral cornea results in a band of tightening and subsequent central corneal steepening and peripheral flattening (Figure 3).
We prefer CK treatment, in spite of its tendency to regress. The main advantage of noncontact CK is that it does not touch the central visual axis. Additionally, no flaps are needed; no lasering or loosening of corneal tissue occurs. It may also be repeated with reproducible results. This 2-minute procedure may be done in the office. Figures 4 and 5 show Pentacam images of a patient who underwent presby-LASIK and one who underwent CK.
Patients in the presbyopic age group cannot afford to be away from work for long, and therefore keratoplasty offers great promise for them.
FUTURE OF PRESBYOPIA TREATMENT
We all know that there is no one-size-fits-all, let alone permanent, treatment available for presbyopia. But keeping ourselves involved with cutting-edge research and continuing to treat patients the way we know how, hopeful we will continue on the path to a better and more permanent solution.
Tejas D. Shah, MD, is the Founder and CEO of Amdavad Eye Laser Hospitals and Good Bye Glasses Laser Centre, Ahmedabad, India, a subsidiary that performs only refractive procedures. Dr. Shah states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +91 79 26307878; fax: +91 79 26303545; e-mail: email@example.com.