Intraocular magnifiers for AMD
Many patients with macular degeneration have severely damaged central vision
Figure A shows the mechanism of action of the OriLens in a schematic. Figure B shows the OriLens device . (Courtesy of OptoLight Vision, Israel)
With 20 million individuals with age-related macular degeneration (AMD)-related sight impairment in Europe, there is a real need for intraocular magnifiers, according to Giuliana Silvestri MD.
“Despite the success of anti-vascular endothelial growth factor (anti-VEGF) therapies, many patients with macular degeneration have severely damaged central vision, either due to geographic atrophy or non-response to treatment for neovascular AMD. Patients are very interested in this technology,” said Dr Silvestri, Belfast Health and Social Care Trust, Belfast, Northern Ireland.
Intraocular magnifying devices have several advantages over external devices currently prescribed for patients suffering from a loss of central visual acuity, she noted.
“There is no relative movement between eye and telescope, which allows for natural scanning of reading material without head movement. The intraocular devices also provide a wider and more comfortable visual field than external devices, allowing for a more intuitive visual experience.”
The implants, which look like complex, technologically advanced intraocular lenses (IOLs), provide a 2.5 times magnification of the incoming image, allowing the image to ‘outgrow’ the confines of the damaged fovea and perifoveal area.
“Although the central scotoma does not go away, it becomes smaller relative to the image projected on the posterior pole,” said Dr Silvestri. “This allows for enhanced central vision. The central scotoma does not disappear, but is rather diminished in size relative to the magnified image being viewed. The trade-off is a constricted, 20-degree field of vision,” she explained.
The telescopes which provide larger magnification are intended for monocular use, as the fellow eye’s peripheral field of vision must be maintained for the ability to navigate.
There are three classes of intraocular magnifying devices: true intraocular telescopes; double-IOL implanted devices with a telescopic effect; and intraocular magnifiers.
The Implantable Miniature Telescope (IMT, VisionCare), one example of a true intraocular telescope, is 3.6mm in diameter and 4.4mm thick (anteroposterior length). Weighing 115mg in air, it weighs more than a Ridley IOL from 1952, which was 108mg. Current IOLs weigh less than 10mg. Implantation requires a 12mm limbal incision and a 7mm capsulorhexis.
The IMT was implanted in 206 patients in a Phase II/III prospective, multicentre study in the USA. Entry criteria included bilateral geographic atrophy or stable disciform scars; distance best corrected visual acuity (BCVA) from 20/80 to 20/800; uncompromised peripheral vision; and at least five-letter improvement on an eye chart using an external telescope.
At one year, 90% experienced two or more lines of improvement of best corrected distance visual acuity, leading to a clinically significant improvement in quality of live. However, 3.6% experienced persistent corneal oedema, and 2.3% required a corneal transplant.
The OriLens mirror telescope (OptoLight Vision), also a true intraocular telescope which is designed using ‘Mirror’ optical principles such as are used in the Hubble telescope, is a secondary, sulcus-implantable piggyback device that provides magnification similar to that of the IMT. However, because of its reduced thickness, at 1.25mm, it requires a smaller surgical incision (6mm), permitting shorter recovery time and a shorter surgeon’s learning curve.
Other systems include the IOL-Vip System (Soleko), and the iolAMD. The IOL-Vip combines a biconcave high minus-power IOL in the capsular bag with a biconvex high plus-power IOL in the anterior chamber. This produces a Galilean telescope effect with 1.3x magnification for distance.
The iolAMD, which combines two posterior chamber IOLs, allows injection through a 3mm incision. This device is intended for bilateral implantation.
The new Scharioth Macula Lens (SML, Medicontur) is a bifocal add-on IOL with a high addition (+10.0D) central optic. Intended for monocular implantation in the better-seeing eye, the SML is the only magnifying device that can be implanted through a microincision (2.2mm).
“Because the peripheral zone of the SML is optically neutral, it affects neither distance vision nor visual field,” said Dr Silvestri.
Dr Silvestri will lead the MIRROR trial, a randomised, controlled trial comparing the OriLens to the current standard of care in end-stage AMD. The primary outcome will be BCVA at 12 months.
“For all these devices, patient selection is absolutely key,” emphasised Dr Silvestri.
Giuliana Silvestri: email@example.com