Implantable Miniature Telescope for End-Stage Age-Related Macular Degeneration
Although promising, current investigations have yet to provide a proven medical or surgical therapy for patients with end-stage, nonexudative age-related macular degeneration (AMD). Patients with this stage of AMD comprise a significant proportion of the visually impaired population.1 These patients often receive rehabilitative assistance in the form of low-vision devices such as portable magnifying glasses, external telescopes, and closed-circuit televisions. These devices may limit patient mobility and require ample manual dexterity in an elderly individual.
The Implantable Miniature Telescope (IMT; VisionCare Ophthalmic Technologies, Saratoga, California) was developed as an alternative visual prosthetic device for patients with end-stage AMD.2 The IMT is composed of a telescopic compound lens system with an anteriorly positioned positive lens and a posteriorly positioned negative lens enclosed in a glass tube which measures 4.4 mm in length and 3.6 mm in diameter. The glass tube is fixed to a polymethylmethacrylate (PMMA) plate with two continuous haptics. The device is implanted after cataract removal using standard phacoemulsification techniques. After adequate conjunctival peritomy, a 10 to 12 mm scleral or limbal incision is made and the device is inserted through the anterior chamber and positioned in the capsular bag. Once positioned correctly in the capsular bag, the device protrudes through the pupil by 0.1-0.5 mm. The scleral or corneal incision is then closed using 6 to 8 sutures. Two device models are available that provide 2.2 or 3 times retinal image enlargement compared to the image normally produced by the cornea and natural crystalline lens. The enlarged, 20o to 24o image field is projected onto 55o of retina and this reduces the peripheral field of view. The device is designed for monocular implantation and the eye with the implant functions to provide high resolution central vision while the fellow eye provides peripheral vision. Postoperative short-term visual rehabilitation training is recommended for proper visual adaptation.
The remainder of this article will summarize findings from a recent phase III study3 evaluating the long-term efficacy and safety of the IMT in patients with end-stage AMD. The trial, conducted by Hudson and colleagues, enrolled 206 patients at 28 centers with a diagnosis of bilateral end-stage AMD (bilateral scotomas resulting from nonfoveal sparing disciform or atrophic AMD). All patients received the prosthesis in one eye and underwent cataract surgery with standard intraocular lens implantation in the fellow eye, which served as the control. Main outcome measures included change in best-corrected visual acuity (BCVA) from baseline, corneal endothelial cell density (ECD), and incidence of complications. The primary efficacy endpoint was a gain of 3 or more lines of distance or near BCVA. The study included phakic patients with baseline BCVA between 20/80 and 20/800 using the Early Treatment Diabetic Retinopathy Study (ETDRS) visual acuity chart. Patients with active choroidal neovascularization (CNV), treatment of CNV in the preceding 6 months, endothelial cell density (ECD) < 1,500 cells/mm2, or anterior chamber depth less than 2.5 mm were excluded from the study. Patients were examined at 1 day and 1 week postoperatively and at months 1, 3, 6, 9, 12, 18, and 24. Thirty-two anterior segment surgeons performed the surgical procedures. Comprehensive pre- and postoperative patient management was provided by retina specialists, anterior segment surgeons, and visual rehabilitation therapists.4
At 24 months, data from 174 (84.5%) of the original 206 implanted patients were analyzed. Of patients not included in the final analysis, ten (4.9%) were deceased, eight (3.9%) had the device removed, 13 (6.3%) were lost to follow-up, and one (0.5%) missed the 24-month visit. Overall, 103 (59.5%) of 173 implanted eyes gained 3 lines or more of BCVA compared with 18 (10.3%) of 174 fellow control eyes (p < .0001). With regard to safety, mean endothelial cell loss was 20% at 3 months, 25% at 1 year, and 27% at 2 years. Endothelial cell loss is believed to be secondary to corneal trauma induced at the time of surgery with no evidence to suggest ongoing endothelial cell damage after 3 months postoperatively. Loss of 3 lines of BCVA occurred in 1 (0.6%) implanted eye compared with 13 (7.5%) control eyes (p=.0013). There were no cases of retinal detachment or visually significant posterior capsule opacification after 24 months of follow-up.
In summary, therapeutic options for patients with end-stage, non-exudative AMD are presently limited. In a prospective, multicenter phase 3 trial, the IMT has shown promising results in terms of visual acuity improvement for these patients. Insertion of the device appears to be relatively safe, but corneal endothelial cell loss due to surgical trauma may restrict implantation to individuals with healthy corneas.
Friedman DS, O'Colmain BJ, Munoz B, et al. Eye Diseases Prevalence Research Group. Prevalence of age-related macular degeneration in the United States. Arch Ophthalmol 2004; 122:564-572.
Lipshitz I, Sheah AD, Loewnstein A. The Implantable Miniaturized Telescope for patients with age-related macular degeneration: design and surgical technique. Operative Techniques in Cataract Refract Surg 2000;3:53-58.
Hudson HL, Stulting RD, Heier JS, et al. Implantable telescope for end-stage age-related macular degeneration: long-term visual acuity and safety outcomes. Am J Ophthalmol 2008:146:664-673.
Lane SS, Kuppermann BD. The Implantable Miniature Telescope for macular degeneration. Curr Opin Ophthalmol 2006;17:94-98.
Hudson HL, Lane SS, Heier JS, et al. 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.
About our author(s):
Ahmad A. Aref, MD
Penn State Hershey Eye Center
Penn State College of Medicine, Hershey, PA