According to a recent estimate, presbyopia affects more than 1 billion people worldwide.1 Although presbyopia affects almost every individual beginning at approximately 40 years of age, few good options exist for surgical correction of presbyopia in the absence of cataract.
Recently, a laser procedure called pressure and accommodation restoration by ciliary translocation (PACT) has shown promise as a noninvasive, laser-based intervention that restores accommodation. This article describes early experience with the procedure and some of the theory behind its mechanism of action.
THE PACT PROCEDURE
In 300 presbyopic patients treated bilaterally over the past 6 years by five European surgeons, including myself, PACT has restored near visual acuity and normalized intraocular pressure (IOP).2 Results were stable for 2 years without the need for retreatment. Although patients' near vision improved from preoperative levels, no changes were seen in distance visual acuity. Experimental data show no postoperative reduction in aqueous production. The implant-free procedure preserves the patient's aesthetic appearance and spares limbal stem cells. No adverse events were seen, and visual rehabilitation occurred by day 1 postoperative.
In the PACT procedure, the Hyperion Ho:YAG laser (PriaVision, San Francisco) is used to create thermal spots on the cornea and in four quadrants in the peripheral sclera. Shrinkage of corneal and scleral tissue causes the tissue to stretch between and beneath the laser spots, the trabeculum, and the ciliary body (Figure 1). The treatment accomplishes several anatomical tasks; it makes the corneal shape more prolate; realigns the ciliary body, thereby increasing circumlental space and zonular tension; and stretches the trabecular meshwork, thereby reducing IOP.
Patients indicated for PACT include emmetropic presbyopes from 40 to 65 years of age, patients with IOPs greater than 21 mm Hg, and established glaucoma patients who are not compliant with their medical regimens.
The PACT procedure is straightforward for both the patient and physician. It begins with instillation of topical anesthetic: proparacaine 0.5% and lidocaine 4%. A speculum is placed on the treatment eye, and the contralateral eye is patched. The patient is seated at the Ho:YAG laser biomicroscope and instructed to focus on a fixation light.
A scleral marker is used to outline the quadrants to which the laser spots will be delivered. Laser spots are delivered transconjunctivally to the sclera in three concentric rows, with the first row 1 mm posterior to the limbus. Approximately five spots, 0.6 mm in diameter, are administered in each row per quadrant, with each spot taking approximately 4 seconds (20 laser pulses).
Topical anesthetic and hyaluronic acid artificial tears are instilled after each quadrant is completed, and the patient re-fixates for each quadrant. The scleral portion of the procedure takes approximately 4 minutes and uses a total of 0.125 J per eye. Laser power is 25 mJ/pulse.
The prolate aspheric shape of the cornea is then enhanced with the application of a ring with a 9-mm diameter of 16 spots on the cornea that takes approximately 6 seconds. These are administered for a duration of 15 pulses per spot with a power of 25 mJ per pulse.
When the first eye is completed, the patch and speculum are swapped, and the contralateral eye is treated. As an option, the thermal lesions on the sclera and cornea can be stabilized by irradiation with ultraviolet A (UV-A) light in conjunction with riboflavin application.
Pain medications are given postoperatively as required. Visual recovery typically occurs in 1 or 2 days, and near vision and IOP improved in less than 1 week.
Figure 2 shows PACT in a 52-year-old woman with near visual acuity of J8 and IOP of 27 mm Hg preoperatively, despite treatment with Xalatan (latanoprost; Pfizer, Inc., New York, New York) and Cosopt (dorzolamide HCl/timolol maleate; Merck & Co., Inc., Whitehouse Station, New Jersey). She received PACT with 15 laser spots in each of the four quadrants. At 1 week after the treatment, her IOP was 18 mm Hg and near visual acuity was J4.
One center has reported results with PACT in 95 eyes (49 patients).2 In this prospective series, follow-up ranged from day of surgery to 11 months postoperative. Out-come measures included improvement in near UCVA and change in IOP from preoperative baseline.
Preoperatively, mean near UCVA was J10 ±4. At 1 week after PACT treatment, mean near UCVA was J5 ±4. At baseline, mean IOP was 15.4 ±2.7 mm Hg. IOP decreased to 12.4 ±2.5 mm Hg at 1 week and measured 12.8 ±2.5 mm Hg at the last postoperative visit.
In a subset of 22 eyes (11 patients) with at least 6 months follow-up, baseline near UCVA was J10 ±4 at baseline and J4 ±3 at last follow-up visit. In this long-term follow-up cohort, baseline IOP of 16 ±3.3 mm Hg was reduced to 12.6 ±2.8 mm Hg at last follow-up visit.
MECHANISM OF ACTION HYPOTHESIS
A hypothesis for the mechanism of action of PACT has been proposed as follows. The ciliary muscle still functions well in the presbyopic patient. The crystalline lens grows with age, but it enlarges more anteriorly than equatorially, leading to misalignment of the zonules with respect to movement of the ciliary muscle. Additionally, the membrane formed by the posterior zonules and anterior vitreous hyaloid stiffens significantly as a person ages, as do the paralimbal sclera and cornea. In this aging, stiffening milieu, the stretching of the trabecular meshwork caused by the shrinkage induced in adjacent paralimbal tissues by PACT increases aqueous outflow. Additionally, the thermal energy from the infrared laser applications reduces the stiffness in local tissues.
PACT represents a highly desirable solution for treatment of presbyopia. It is minimally invasive, involves no implant, spares the aesthetics of the patient (with no scleral scars or erythema), and conserves the patient's distance UCVA and manifest refraction spherical equivalent. After approximately 1 day of recovery, the patient achieves functional near and intermediate vision with no loss of contrast sensitivity or increase in higher-order aberrations. Stability is demonstrated for up to 1.5 years.
Preliminary results suggest that PACT achieves rapid restoration of near UCVA and normalization of IOP with no safety issues identified. The explanation for the efficacy of PACT appears to be most consistent with the modified geometric theory of presbyopia proposed by Strenk and colleagues.3
The corneoscleral shrinkage induced by PACT may be a safe and effective approach for both restoration of accommodation and treatment of elevated IOP. Further study of the safety and efficacy of PACT for these indications in the setting of a prospective controlled clinical trial is warranted. The use of corneoscleral collagen cross-linking using UV-A and riboflavin is currently being investigated.
A. John Kanellopoulos, MD, is a corneal and refractive surgery specialist. Dr. Kanellopoulos is Director of Laservision Eye Institute in Athens, Greece, and practices in New York as well. He is an Attending Surgeon in the department of ophthalmology at the Manhattan Eye, Ear, and Throat Hospital in New York and a Clinical Associate Professor of Ophthalmology at New York University Medical School. He is a member of the CRST Europe Editorial Board. Dr. Kanellopoulos states that he has no financial interest in the products or companies mentioned. Dr. Kanellopoulos may be reached at tel: +30 21 07 47 27 77; e-mail: email@example.com.
- Holden BA. Fricke TR, Ho SM, et al. Global vision impairment due to uncorrected presbyopia. Arch Ophthalmol.2008;126(12):1731-1739.
- Kanellopoulos AJ. Pressure and accommodation restoration by ciliart translocation (PACT). Paper presented at: Presbyopia International; September 12, 2008; Berlin, Germany.
- Strenk SA, Strenk LM, Koretz JF. The mechanism of presbyopia. Prog Retin Eye Res. 2005;24(3):379-393.