A new device can partially restore central field vision to thousands who suffer from a common cause of blindness
The Hubble, an enormous telescope orbiting the globe, is a wonder of 20th century science that allows us to see far into the cosmos. On a totally different scale, medical scientists have developed the smallest telescope for human use, a telescope that can be surgically implanted in the human eye to restore lost central vision!
The most common cause of central vision loss is macular disease, both hereditary and acquired. These diseases result in the loss of high-resolution vision. The incidence rises rapidly with age from about 1 percent in 55-year-olds to an estimated 15 percent of those 80 and older.
The most common of the macular degenerative diseases is age-related macular degeneration (AMD); it affects about 8 million Americans. The vision that is lost is in the central field; peripheral vision is relatively spared.
In early-stage AMD there are a few therapies that can offer some help, but once the damage is done and the vision loss is stable, the treatments have been functional, i.e. head-mounted or hand-held magnification devices, until now.
Recently VisionCare Ophthalmic Technologies, a small company in Saratoga, Calif., was awarded FDA approval for an implantable miniature telescope (IMT). The approval is specifically indicated for monocular implantation to improve the vision in patients age 75 or older with stable severe-to-profound vision impairment caused by end-stage age-related macular degeneration resulting in blind spots called bilateral central scotomas. The goal of the device is to improve middle to distant vision. The range of impairment in the FDA label is from 20/160 to 20/800 on the traditional vision chart (think big E). About a half-million patients meet the label indication of age and severity for the IMT.
A tiny telescope is implanted in place of the eye’s lens.
A 24-month clinical trial for the IMT was held at 28 medical centers over five years. The study used the terminology “eyes” in all of the reporting, something that may seem a bit odd to the readers but nonetheless is the jargon used by the investigators. Remember that since the device could only be implanted in one eye per patient, the “eyes” are directly translatable to patient numbers.
The primary endpoint in the clinical trial was an improvement of two lines or better as measured on the vision chart. For distance vision, this endpoint was met by 75 percent of the participants.
Of note is that 60 percent of patients gained three or more lines of visual acuity, 40 percent gained four or more lines, and 20 percent gained five lines. When a traditional set of glasses was used, near vision gains were similar. Patients felt that their quality of life was improved significantly.
This device is not implanted without adverse events. Some of the events were significant and led to removal of the IMT in eight patients. Four of the eight had the telescope removed at their request because of an inability to adapt (more about this later).
Two telescopes were removed because of condensation of fluid within the telescope optics and two because of decompensation of the cornea. An additional two failed because of a broken attachment lead. Another adverse event is the decrease in endothelial cells within the eye. This appeared to be related to the amount of experience the surgeon had and appeared to diminish as the surgeons gained experience.
Two levels of magnification are available: 2.2x and 2.7x. Patients were given trials of external magnifying devices with these two powers and allowed to choose.
It has three parts: small attachment loops, a light restrictor that surrounds it, and a fused capsule holding the two lenses that create the magnification. Because the device contains stainless steel, no MRIs may be conducted until further studies are completed. The device is much larger than the typical cataract lens, which explains some of the adverse events.
The IMT projects an enlarged image onto the part of the retina that is still functional. Because the brain typically attempts to use the central vision to do most of its “seeing” even when the central vision has been destroyed by the primary disease, the brain must be trained to use the part of the retina that is still functioning.
The FDA approval contained a provision that requires patients who wish to be considered for this implant to undergo special training by a low vision expert before implantation. This training speeds adaptation to the device after implantation and can weed out those who do not seem capable of adapting.
Since the device is only indicated for use in one eye, the remaining eye is used for peripheral vision. The brain actually reprograms itself to use the two eyes independently, similar to the way that people adapt to a near and far contact lens for more modest vision impairments.
Contraindications include, but are not limited to, prior intraocular surgery, prior corneal surgery, steroid-induced intraocular pressure rise, uncontrolled glaucoma, significant myopia or hyperopia, diabetic retinopathy, optic nerve disease, and retinal detachment.
The approval of the IMT has opened a treatment option to patients who have significant vision loss that has been basically untreatable without large external magnification devices. Although the device has a rather tight FDA approval and some significant adverse events, it does constitute another advance into Tomorrow’s Medicine!
For further reading
- VisionCare Ophthalmic Technologies, Inc. Completed Modular PMA Shell Number M050004/M004. http://bit.ly/gEqqgu/ Verified Dec. 1, 2010
- FDA Executive Summary. Prepared for the March 27, 2009 meeting of the Ophthalmic Devices Panel. http://bit.ly/fYp5zd/ Verified Dec. 1, 2010
- Premarket approval application letter. http://bit.ly/e6p0HW/ Verified Dec. 1, 2010