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Mirror telescopic IOL may help patients with AMD, other macular pathologies
Researchers have good results, few complications in the first trial of the Lipshitz Macular Implant.
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Macular pathologies cause a great amount of morbidity worldwide and have significant impact on community health. Age-related macular degeneration is the leading cause of legal blindness in the industrial world. AMD has been divided into dry (nonexudative) and wet (exudative) types.
Recently, an AMD prosthetic device, the Implantable Miniature Telescope (IMT), invented by Isaac Lipshitz, MD, was tested. The drawbacks encountered with the IMT included loss of peripheral vision in the implanted eye, a difficult surgical technique, endothelial compromise (Figure 1), blocked peripheral retinal visibility, difficulty in future retinal laser treatments, difficulty due to the size and weight of the implant, and severe aniseikonia due to the disparity of the images in the two eyes.
To solve these problems, a new IOL was designed that magnifies the image on the retina based on a mirror telescope — the Lipshitz Macular Implant, or LMI. The implant was designed by Dr. Lipshitz. We aimed to test this IOL not only on patients with dry or wet AMD but also other diseases that affect the macula, thus affecting central vision. This was the first experimental trial of this novel surgical implant.
Mirror telescopic IOL
The LMI is a regular IOL that incorporates two miniature mirrors in a Cassegrain telescopic configuration. These mirrors act by modifying the reflected image on the retina (Figure 2). The IOL has a dual optical system that ensures that light passing through the center of the optic is magnified by the Cassegrain telescope, whereas the light passing through the periphery passes through the normal IOL configuration. Overall diameter of the IOL is 13 mm, and the size of the optic is 6.5 mm. The anterior, central mirror size is 1.4 mm. The posterior mirror is doughnut shaped and 2.8 mm in diameter with a central clear area of 1.4 mm in diameter. The peripheral zone of the optic is similar to a normal IOL for undisturbed peripheral vision. The reflecting surfaces of the LMI are coated with multiple layers of TiO2 and SiO2 (dielectric coatings), thus creating the mirror effect. The thickness of these mirrors is only 1 µm to 2 µm. The entire IOL is coated with Parylene C (poly-para-xylene) for biocompatibility.
The LMI was designed to have magnification of 2.5 times, ie, it magnifies the central image on the retina by 2.5 (Figure 3). The subject thus sees a magnified central image through the mirror telescope and a normal non-magnified image through the periphery of the IOL, thus increasing the magnified central vision while maintaining the orientation in space due to normal peripheral vision. Testing was done in the lab while preparing the IOL (Figure 4).
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Images: Agarwal A |
Patient selection criteria
Patients were selected if they had bilateral macular pathologies with visual acuity less than 20/200, cataract less than grade 2, no other ocular or systemic diseases and vision that improved when tested with 2.5-times external telescope preoperatively. Informed consent was taken from all patients after explaining potential benefits and possible complications of the procedure. Patients’ motivation, communication skills and availability for follow-up to 12 months were considered before appointing them for study.
Surgery
All surgeries were performed by the same surgeon (Prof. Amar Agarwal). Conventional phacoemulsification or 700-µm cataract surgery (microphakonit) was performed (Figures 5 and 6), or coaxial phaco was done. The corneal tunnel was increased with a diamond knife or regular keratome to 6.5 mm, and the IOL was placed in the bag. One patient was pseudophakic, and in that case explantation of an existing IOL was performed followed by implantation of the LMI (Figures 7 to 9).
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Results
Six eyes of six patients having macular pathologies were implanted with the LMI. Postoperatively, we observed improvements in distance visual acuity up to 6 months. Two of the patients had initial loss of lines in the operated eye when measured 1 week postoperatively, which improved after 1 month in one patient and 6 months in the other patient. At the end of 6 months, none of our patients had any decrease in distance visual acuity. The mean postoperative distance visual acuity at the end of 6 months was 0.133 as compared with 0.067 preoperative values.
The eyes were evaluated for endothelial cell density and loss. The mean endothelial cell count in operative eyes was 3,018.33 ± 513.09, which at the end of study was 2,842.66 ± 593.01. The mean change in operative eyes was –5.79% ± –4.07%.
All of the patients were found to have anterior chamber depth within normal range. Photos of anterior segment optical coherence tomography (Figure 10) show normal position of the LMI and normal anterior chamber dimensions.
Fundus evaluation of all patients was done by the same retina specialist in order to grade the difficulty in fundus examination using indirect ophthalmoscope and to assess the possibility of future retinal photocoagulation for peripheral retinal pathology. It was found that the difficulty level encountered was grade 1 in all the quadrants. Good central fundus view was also possible in all the patients.
Grading system for accessing ease of fundus evaluation:
Grade 0: No difficulty, ora seen
Grade 1: Ora seen but with problem of glare
Grade 2: View up to mid-periphery only
Grade 3: View up to equator only
Grade 4: Only central fundus seen (disc and macula)
Discussion
Patients with AMD usually have difficulty reading and seeing near objects, such as the inability to recognize faces clearly. Other macular pathologies will also cause similar difficulties with varying degree of severity. Optical modalities available to improve the size of an image on the central retina in these patients, such as low-vision aid loops and magnifiers, can be used. But this is all at the expense of loss of field of vision and depth of focus. In addition, the short reading distance, distortion of images, weight and large size are problems associated with these devices. Some new devices, such as the head-mounted video-based image processing system, are also available. But the problem of handling, which is the most common cause of failure of low-visual aids, is associated with them also. The IMT was used previously with limited success. The new implant is free from the complications associated with the IMT.
The LMI is similar to a regular IOL used after phacoemulsification and is fully placed in the bag in a similar way. It provides a magnified central image up to 2.5-times normal while maintaining the normal peripheral vision through the peripheral portion of the lens, unlike the IMT. Because of this, it can be used in both eyes of a patient. If there is any further deterioration of the macula, increased magnification can be achieved by adding plus eyeglasses up to +4 D range.
There is no relative movement between the eyes and the LMI, unlike an external telescope. It requires a 6.5-mm corneal incision, unlike the incision of at least 10 mm for the IMT, thus reducing surgically induced astigmatism. In this study, we found the postoperative examination of these patients easier with only minimal glare problems due to inadvertent reflection from the mirrors. This provides no difficulty for future retinal photocoagulation in contrast to IMT, which has a limited possible fundus of view. Fluorescein angiography results of patients show good visibility of the retina up to mid-periphery in experienced hands, as shown in the photos. Photographs taken from the center of the lens had a reflex due to reflection from the posterior mirror blocking the visibility up to half of the view, but those taken from the periphery of the optic after complete pupil dilatation had a satisfactory retinal view. No significant endothelial loss was noted, as the surgery was similar to conventional surgeries for IOL implantation after phacoemulsification and the size of the LMI was small as compared with the IMT.
For more information:
- Amar Agarwal, MS, FRCS, FRCOphth, can be reached at Dr. Agarwal’s Eye Hospital, Cathedral Road, Chennai-600086, Tamil Nadu, India; e-mail: dragarwal@vsnl.com.
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