The Merits and Limitations of the Implantable Miniature Telescope for AMD
CONTROVERSIES IN CARE
The Merits and Limitations of the Implantable Miniature Telescope for AMD
Edited by Michael Colucciello, MD
Nearly two million individuals in the US have advanced age-related macular degeneration, a number expected to climb to nearly three million by 2020.1 500,000 new cases occur each year.2 A study published in 1998 suggested that up to approximately 50% may eventually have bilateral disease,3 rendering significant effect on these bilaterally affected individuals' daily living, independence and mood.
Patients with bilateral central scotomas secondary to advanced AMD often respond well to magnification. Prescribed external vision appliances such as handheld magnifiers and spectacle-mounted telescopes provide functional benefit for many. Unfortunately, others are troubled by nausea associated with the magnification-related vestibular ocular reflex, lack of portability of some of the magnification devices, and cosmetic appearance of the spectacle-mounted telescope.
The implantable miniature telescope (IMT) attempts to overcome these problems. The IMT is placed into the posterior chamber of the anterior segment after a 12-mm superior limbal incision and lens extraction with a large (7mm) capsulorrhexis.4 The IMT is composed of a PMMA carrier, a compound lens system with an anterior positive lens and a posterior negative lens sealed in a glass tube, with a blue lens ring to reduce glare.4
The IMT is designed for monocular use in patients with a central scotoma due to bilateral AMD. Two models are available, projecting a 2.2x or 2.7x magnified image on the surface of the retina.
The FDA approved the device on July 1, 2010 after pro spective studies5,6 demonstrated benefit from a visual perspective.
This translated into improved activities of daily living that surpassed concerns regarding the average 13% to 25% corneal endothelial loss after 12 months of implantation.5,6 Conditions that patients must satisfy to be in accordance with FDA approval include7:
• Patients greater than or equal to 75 years of age.
• Stable severe to profound vision impairment (bestcorrected distance visual acuity 20/160 to 20/800).
• Bilateral central scotomas associated with end-stage age-related macular degeneration.
• Geographic macular retinal pigment epithelial/choriocapillaris retinal atrophy or disciform scar with foveal in volvement, as determined by fluorescein angiography.
• Patients must have evidence of visually significant cataract (> grade 2).
• Patients must agree to undergo pre-surgery training and assessment (typically two to four sessions) with low vision specialists (optometrist or occupational therapist) in the use of an external telescope sufficient for patient assessment and for the patient to make an informed decision.
• Achieve at least a five-letter improvement on the ETDRS chart with an external telescope.
• Have adequate peripheral vision in the eye not scheduled for surgery.
• Agree to participate in postoperative visual training with a low-vision specialist.
In this month's “Controversies in Care” column, Paul Sternberg, MD, with Jeff Sonsino, OD (both of Vanderbilt University) and Donald Fletcher, MD, with August Colenbrander, MD (of Smith-Kettlewell Eye Research Institute) participate in a pro/con debate based on their experience.
1. Friedman DS, O'Colmain BJ, Muñoz B, et al.; Eye Diseases Prevalence Research Group. Prevalence of age-related macular degeneration in the United States. Arch Ophthalmol. 2004;122:564-572.
2. Klein R, Klein BE, Jensen SC, Meuer SM. The five-year incidence and progression of age-related maculopathy: the Beaver Dam Eye Study. Ophthalmology. 1997;104:7-21.
3. Wang JJ, Mitchell P, Smith W, Cumming RG. Bilateral involvement by age related maculopathy lesions in a population. Br J Ophthalmol. 1998;82:743-747.
4. Colby KA, Chang DF, Stulting RD, Lane SS. Surgical placement of an optical prosthetic device for end-stage macular degeneration: the implantable miniature telescope. Arch Ophthalmol. 2007;125:1118-1121.
5. Lane SS, Kuppermann BD, Fine IH, et al. A prospective multicenter clinical trial to evaluate the safety and effectiveness of the implantable miniature telescope. Am J Ophthalmol. 2004;137:993-1001.
6. Hudson HL, Lane SS, Heier JS, et al.; IMT-002 Study Group. Implantable miniature telescope for the treatment of visual acuity loss resulting from end-stage age-related macular degeneration: 1-year results. Ophthalmology. 2006;113:1987-2001.
7. FDA approval letter for Implantable Miniature Telescope. Food & Drug Administration Web Site. http://www.accessdata.fda.gov/cdrh_docs/pdf5/P050034a.pdf. Accessed August 6, 2010.
STERNBERG & SONSINO
Despite advances in the treatment of neovascular agerelated macular degeneration, there remain a large number of patients with advanced disease, be it from residual disciform disease prior to the development of anti-VEGF therapy, inactive neovascular disease following successful (or failed) anti-VEGF therapy, or advanced atrophic AMD with central geographic atrophy. All of these patients suffer impaired quality of life, with limitation of daily activities such as reading and driving. While conventional low vision rehabilitation therapy, including magnifying glasses, closed-circuit television systems, or external bioptic telescopes, can be quite helpful, patient compliance and acceptance is variable. There is little doubt that there is considerable room for advances in the care of patients with vision loss from advanced AMD.
The Implantable Miniature Telescope (IMT) was developed by Dr. Isaac Lipshitz and VisionCare Ophthalmic Technologies to address these challenges. The device is implanted at the time of cataract surgery, creating an internal optical system that projects an enlarged image onto the
retina, thus reducing the size of the scotoma relative to the object in the central visual field. The eye sees a wider field of view due to the large image projection, ranging from 2.2x to 3x magnification. With the IMT recently receiving FDA approval for implantation, the precise role for this
device in the management of AMD patients re mains to be defined. Given the relatively small total number of patients who received the implant — 206 eyes — no individual center or physician has had broad-based or extensive experience. However, several observations seem justified and relevant for physicians counseling patients who may be considering implantation.
1. Although there may be a learning curve for the cataract surgeon, the IMT can be implanted safely. As cataract surgery has evolved toward increasingly smaller incisional techniques, many surgeons have limited experience with this type of surgery. IMT implantation requires a considerably wider incision, reflecting back to the planned extracapsular or even intracapsular surgery era. A lead inves tigator
for the phase 2/3 study, Stephen Lane, MD, writes, “Successful implantation requires considerably more skill, time, and intensity than (conventional) intraocular lens (IOL) implantation.”
2. While corneal endothelial cell loss is a concern, the majority of the damage occurs at the time of implantation. In the phase 2/3 study, mean corneal endothelial cell density (ECD) decreased from 2,492 cell/mm2 preoperatively to 1,994 at three months, 1,936 at six months, and 1,870 at 12 months. Thus, while there was 20% loss in the first few months, mean ECD stabilized thereafter. These findings suggest that preoperative corneal health is essential. In addition, however, careful surgical technique is critical to minimize damage at the time of implantation. Review of study patients showed that surgeons had greater endothelial cell loss in their first three cases.
3. Appropriate patient selection and the setting of realistic patient expectations are critical in predicting success in acceptance of the new optics. It is apparent that not every patient with advanced AMD will be tolerant of the IMT optics. Currently, data does not exist to suggest whether patients with one form of disease are better candidates than another, eg, geographic atrophy vs disciform scar. While scotoma size
likely has some bearing on likelihood of successful rehabilitation, microperimetry was not performed routinely on study patients. A better predictor of success may be related to findings and counseling at the time of preoperative low vision evaluation. Specifically, dominance testing and eye
selection appears to be critical in determining postoperative success. Although the IMT-002 trial protocol dictated that the worse-seeing eye was im planted (irrespective of eye dominance), retrospective review of the trial participants at one site indicated that success may be better if the dominant eye is chosen for implantation.1
Preoperative testing should also include simulation with external telescopes to help guide expectations. In the IMT-002 study, a standard external telescope was used to simulate implantation with the device. There were numerous optical limitations of this simulation, including decreased
field of view and reduced ability to scan. In the current IMT-UK study, an external telescope simulator (ETS) has been developed to better simulate telescope correction externally.
4. Intense postsurgical rehabilitation by a patient and capable low vision specialist will improve quality of life for the impaired individual. By design, patients will have severe diplopia following implantation. The non-implanted eye will be useful for peripheral vision. The implanted eye will have either 2.2 or 3x magnification, resulting in anisokonia, or differing retinal image sizes between the two eyes. Because the brain cannot fuse these images, the patient must be taught to reconcile this effect. Postsurgical rehabilitation also includes prescription of spectacles and low-vision devices to enhance the usability of the implanted telescope, such as high-add readers for near work.
5. With a collaborative and talented multidisciplinary team, the IMT will be a valuable addition to the armamentarium of treatments for the AMD patient. The findings of the phase 2/3 study clearly demonstrated significant improvement in visual acuity with the IMT. However, this result will not always correlate with patient acceptance of the device and concomitant improvement in quality of life. It is critical for the retinal surgeon to work closely with the low vision specialist to ensure that the patient understands the limitations of the device and has a reasonable likelihood of tolerating the new optical system.
The cataract surgeon must assess corneal endothelial status and be skilled at performing a minimally traumatic implantation. Intense postoperative visual rehabilitation with the help of an occupational therapist is essential. With these constraints, the IMT can provide a significant
improvement in quality of life for the patient disabled by advanced age-related macular degeneration.
1. Lane SS, Kuppermann BD. The Implantable Miniature Telescope for macular degeneration. Curr Opin Ophthalmol. 2006;17:94-98.
2. Primo SA. Implantable miniature telescope: lessons learned. Optometry. 2010;81:86-93.
FLETCHER & COLENBRANDER
The advent of intraocular telescopes for AMD, the recent FDA approval of the IMT, and the ensuing publicity have created great interest in this option among ocular surgeons as well as among patients. As ophthalmologists involved in vision rehabilitation, we feel compelled to voice our concerns. Our intention is not to stifle innovation, but to present a balanced perspective. We have several reasons for uneasiness.
There are some important considerations that have been left unaddressed in attempting to solve the functional difficulties of low-vision patients by implanting an intraocular telescope. While the IMT has been shown to improve the ability to read smaller rows of letters on an acuity chart, the bottom line should be, does it translate into improved performance in real-world activities of daily living (ADL)?
Exchange of Resolution Benefit for Decreased Field of Vision. Gains in resolution ability come at an expense — it is impossible to use a telescope to accomplish magnification without a resultant loss of visual field. While this loss of field is monocular, it is nonetheless a loss of field in an eye that previously had a full peripheral field. Can we be sure that the fellow eye will be able to compensate adequately, not only in the immediate postoperative period but also later as pathologies continues to progress? Is this full-time reduction of field diameter merited by the resolution gain? Is it necessary or even valuable to have full-time magnification for distance activities?
A potential advantage of the IMT is its ability to offer distance magnification. In the senior population, distance magnification is often simply not required. The prime need for distance magnification is in reading signs in unfamiliar areas. The sphere of travel tends to shrink with increasing
age and most travel is in very familiar areas. Visual field is more important for safe mobility and orientation than resolution, anyway. It seems more reasonable to use the full field of vision of the “natural” eye and simply keep a portable mo nocular telescope in your pocket or purse for the occasional time that a sign needs to be read.
No Advantage for Magnification for Reading and Other Near Detail Activities over Convention Devices. Most tasks that require fine detail vision are done at a close distance and while stationary, such as reading, writing or sewing. Magnifiers of various styles are effective for these tasks and afford the flexibility of easily being changed/strengthened should the disease progress. Macular diseases commonly increase the threshold sensitivity of the macular and the prime rehabilitation adaptation is illumination. Many magnifiers have effective built-in illumination, while the IMT does not address this issue. These highly effective magnifiers are generally available for under $100, which is a considerable saving vs $15,000 for the IMT.
Issues of Central Visual Field Disruption. Studies of low vision rehabilitation patients have consistently demonstrated that well over 80% have significant central field disruption. A majority do not have a functioning fovea and require an eccentric preferred retinal locus (PRL) to be developed.1 The IMT may make central visual field issues worse rather than better. Points to consider include:
• Intact foveal vision with paracentral scotomata. In this situation visual acuity may be good, but reading may be difficult because the intact retinal area is so small. This condition asks for rehabilitation training, rather than optical devices. Larger letters in the small central island would be counterproductive.2
• A relative central scotoma, with retained central fixation. In this situation, magnification with the IMT may be helpful
and retraining of fixation behavior is not necessary. For these patients, though, illumination is far more valuable than magnification. This condition has become more common since the advent of anti-VEGF treatments.
• An absolute central scotoma. If the telescope is properly centered, the position of the retinal image will not change. The scotoma forces the patient to use eccentric fixation. Since the resolution of the peripheral retina is less, this requires magnification, but equally important is vision rehabilitation training to establish a new fixation and new saccadic behavior patterns.
Age-related Macular Degeneration is not a Stable Condition. The vast majority of low vision rehabilitation patients in Ameri ca have AMD. This condition can be progressive over the course of a patient's life. By trapping the low vision enhancement device in the patient's eye, a solution that works well initially may present a problem when it is no longer optimal with progression of the disease. Addition of stronger magnification on top of the IMT may potentially be problematic.
The experience in our low vision practice is that only one in six patients are satisfied with 3x magnification or less.3 The other five require more or substantially more. Considering the fact that AMD is a progressive disease, we wonder how long patients will consider a 3x telescope
satisfactory. Even if a 3x telescope will allow the use of a weaker magnifier, is this enough of a benefit to outweigh the other considerations?
The Importance of Training. Different forms of AMD have different functional effects. Most of these require both magnification and training. One without the other will not produce optimal results. Much has been published about the surgical technique, but little detail is available about the required vision rehabilitation training.
The Relative Role of the Treatment Components. All papers on this subject report that the patients saw better and felt better after surgery than they did before. However, they fail to separate the factors that contribute to this improvement:
• Removal of a cataractous lens.
• Insertion of a telescopic device.
• Rehabilitation training before and after surgery.
By not separating these factors, it is impossible to estimate how much improvement can be attributed to each.
Experienced surgeons should be able to give an estimate of the number of lines of improvement that can be expected from cataract surgery alone. This number is not reported.
The expected improvement from telescopic magnification is easily calculated. A 2.2x or a 2.7x telescope is expected to be 3.5 or 4.5 lines of improvement. We would therefore expect that the improvement from the telescope alone would be at least three lines. That only 60% of the successfully implanted patients achieved this level is disappointing.
Safe and Effective? While we are not impressed with the effectiveness, considering that in 5% of the originally enrolled patients, the procedure was aborted for various reasons and that in an additional 4%, the IMT later had to be explanted. This also puts a question mark on the safety. The safety record of the IMT must be compared to that of regular cataract surgery and to traditional low vision de vices, which have no risk at all.
Screening and Selection.We are encouraged by the fact that the FDA has requested better screening criteria and that the company has plans to implement those. Criteria should be established, not only for the selection of patients, but also for the qualifications of the surgeon (few of today's surgeons are experienced with large-incision cataract surgery any more) and for the vision rehabilitation team.
We have heard that only a small percentage of potentially interested patients will qualify. This means that more detailed information about the screening and selection process is needed, especially to inform general ophthalmologists and retina specialists, outside the IMT teams, since
they are the ones who will need to give satisfactory answers to the vast majority of patients who will not qualify.2 RP
1. Fletcher DC, Schuchard RA. Preferred retinal loci relationship to macular scotomas in a low-vision population. Ophthalmology.1997;104:632-638.
2. Fletcher DC, Schuchard RA, Watson G. Relative locations of macular scotomas near the PRL: effect on low vision reading. J Rehabil Res Dev.1999;36:356-364.
3. Colenbrander A. Measuring vision and vision loss. In: Duane's Clinical Ophthalmology. Duane TD, Tasman W, Jaeger AE, eds. Philadelphia, Pa: Lippincott Williams & Wilkins; 2010.
Retinal Physician, Issue: October 2010