Because of the large number of patients who will need cataract surgery, many companies are designing presbyopia-correcting devices.
Take-home message: Because of the large number of patients who will need cataract surgery, many companies are designing presbyopia-correcting devices.
Focus on Refractive Surgery By Ehsan “Ethan” Sadri, MD, FACS
Beach, CA-A “typical” patient who comes in for cataract surgery has extremely high expectations regarding the visual outcomes at all visual distances and is not willing to settle for less.
Because of the large number of patients who will need cataract surgery, the pool of patients willing to spend money on the most advanced technologies to provide the highest level of vision is expanding exponentially.
With this potential market, many companies are designing presbyopia-correcting devices, and the attention they are getting is just the tip of the iceberg. In excess of 100,000 inlays have been implanted worldwide. The devices are currently approved in 51 countries in Europe, the Asia-Pacific, the Middle East, North and South America, and India. But this is just the beginning.
Product milestones in this area include development of the:
The devices that are further along in the testing process are highlighted in this article.
This inlay-which is on the verge of approval by the FDA-is made of polyvinyledene fluoride and carbon nanoparticles and is highly biocompatible. The device improves near vision by extending the depth of focus. A typical patient with presbyopia may have only 0.25 D of depth of focus. Following implantation of the Kamra inlay, that can increase to in excess of 2.5 D.
The central aperture is a hole in the inlay that has no power. The inlay is designed to provide an unobstructed pathway for focused light to reach the retina. Advantages are its small size with a diameter of 3.8 mm, a 1.6-mm aperture, and a thickness of only 5 µm. The device has 8,400 holes ranging in size from 5 to 11 µm, which provide its high permeability.
Two surgical procedures can be used to implant the Kamra inlay, i.e., in a pocket or a dual interface. The former approach, which can be used with emmetropic presbyopes, involves creation of a pocket about 200 to 250 µm deep in the stroma into which the inlay is placed.
The latter surgery is good for patients with ametropic presbyopia and presbyopia who had undergone a LASIK procedure or were to undergo a LASIK-Kamra procedure. With the combination procedure, LASIK is performed under a 100-µm flap. With the other approach, a minimum of 1 month after LASIK, a pocket is created 100 µm under the LASIK interface and the inlay is inserted.
The mean near uncorrected visual acuity that is achieved is quite good at J2 12 months postoperatively. Importantly, at the same time point the uncorrected distance visual acuity remains stable at about 20/30. Patients with the inlay implanted in a pocket had no change in the mean distance stereoacuity scores between preoperatively and 6 months after implantation of the inlay.
At 2 years post-implantation, the ease of performing distance visual tasks remained stable after implantation of the inlay using a pocket procedure. Patients rated the ease of performing near visual tasks with both eyes without wearing glasses as 7 on the ranking scale, with 1 indicating “not easy at all” and 7 “very easy.”
Investigators have reported a small decrease in the photopic and mesopic contrast sensitivity, but the values are within the normal range 2 years postoperatively.
However, at the end of the day compared with the benefits provided by the inlay the reduction in contrast is considered minor.
Patients also reported a low incidence of visual symptoms 2 years after surgery that included glare, halos, and night-vision problems. In line with these positive results, patients reported significantly increased reading speed and reading ability and decreased distance at which they could read.
The increased reading ability at J2 after implantation was sustained out to 5 years postoperatively.
Another benefit of the technology is that the procedure is reversible and does not restrict future refractive options.
Cataracts and lens opacities can be seen easily through a dilated pupil with the implant in place. When a patient with a Kamra inlay develops a cataract, there are several options- namely, performance of phacoemulsification and implantation of a monofocal IOL with the inlay in place, removal of the inlay after implantation of a monofocal IOL, and removal of the inlay followed by implantation of a posterior chamber IOL.
While this was the first and most extensively used of the inlays, it still is not approved in the United States.
This corneal inlay is constructed from a permeable hydrogel with the same refractive index as that of the cornea. The device is 2 mm in diameter and the central thickness is 32 µm. This inlay affects the patient’s accommodative power by causing the central radius of corneal curvature over the implant to increase in the non-dominant eye. The inlay is implanted under a corneal flap created by a femtosecond laser.
Study of this inlay is still in its infancy:
The uncorrected distance visual acuity also improved significantly and remained stable out to the 12-month visit.
This device is made of a hydrophilic polymer (hydroxyethylmethacrylate and methylmethacrylate), is 3 mm in diameter, and only 20 µm thick at the edges. The microlens is designed to change the refractive power in the center of the cornea to facilitate near visual function. The device is implanted using an injector roughly 300 µm deep into a corneal pocket created using a femtosecond laser.
In a study of 47 patients with emmetropia, Limnopoulou et al. (J Refract Surg. 2013; 29:12-28) reported that 1 year after implantation of the microlens, the mean uncorrected near vision had improved significantly compared with preoperatively. The mean uncorrected distance vision decreased significantly following implantation in the eye that received the implant, but the binocular distance vision did not change substantially.
The synthetic corneal onlay differs from inlays because it is implanted in a pocket in the outer corneal tissue rather than under a flap.
The procedure-which is adjustable and reversible-is minimally invasive to the central optical zone. The epithelium in the central cornea is debrided and the lenticule is placed on the exposed stroma where the pocket maintains the position of the onlay. This pocket then holds the onlay in place until the disturbed epithelial cells grow back to cover the device.
The device is comprised of a genetically engineered material resembling collagen.
Currently, the microlens has not been tested in humans, only experimentally. In a study in which the device was implanted in cats, the investigators found that the epithelium began to regrow as soon as 1 to 2 days after implantation and after 5 to 11 days full epithelialization had taken place (Evans et al. Invest Ophthalmol Vis Sci. 2002;43:3196-3201). This onlay has been on hold because of other competing technologies.
The future of presbyopic correcting inlays is very strong. The promise of having excellent near vision independent of lens replacement is soon to be a reality.
In addition, the competing technologies will allow the best results as choices for surgeons for their patients.
Ehsan “Ethan” Sadri, MD, FACS
Dr. Sadri is in private practice in Newport Beach, CA. He did not indicate any proprietary interest in the subject matter.