August 2007

 

CATARACT/ IOL

 

Perspective in lens and IOL surgery

LMI … a new mirror telescopic IOL


by Professor Amar Agarwal, M.S., FRCS, FRCOphth

 

Dr. Amar Agarwal, from Chennai, India, has been very active internationally in cataract and refractive surgery, as well as posterior segment surgery. He is a prolific author in addition to being a researcher, teacher, surgeon, and clinician. He is, perhaps, best known as the individual who has brought wider recognition and utilization of the technique of bimanual microincision phacoemulsification, first published in 1973 by JP Shock, again in 1974 by Louis Girard, in 1985 by Steven Shearing, and finally, by Tsutomu Hara in 1989. In this month’s column, he is going to describe an improvement over the original implantable miniature telescope, which was a great advancement in that it gave AMD patients a magnified central image, but in order to achieve this, the device deprived patients of their peripheral vision. This new device preserves peripheral vision while giving the macular magnification that AMD patients appreciate.

I. Howard Fine, MD, Column Editor

 

A new solution for the optical rehabilitation of patients with age-related macular degeneration and other macular pathologies.

Figure 1- The new mirror telescopic IOL -LMI (Lipschitz macular implant) (US patents filed). Illustration depicts how the IOL magnifies the central image on the retina

Figure 2- LMI implanted after 700 micron cataract surgery. One can also do this after co-axial phaco.

Macular pathologies cause a great amount of morbidity and mortality world wide and have significant impact on community health. Age-related macular degeneration (AMD) is the leading cause of legal blindness in the industrial world. To help solve this problem, a new IOL, designed by Issac Lipschitz from Israel, magnifies the image on the retina based on mirror telescope: the LMI-Lipshitz Macular implant. This is not the same as the AMD prosthetic device, Implantable Miniature Telescope (IMT), also developed by Dr. Isaac Lipshitz. Among the first cases using the LMI were performed in India.

LMI mirror telescopic IOL

The LMI is a regular IOL that incorporates two miniature mirrors in Cassagrain telescopic configuration. These mirrors act by modifying the reflected image on the retina. (Figure 1) The IOL has a dual optical system which ensures that light passing through the center of the optic is magnified by the Cassagrain telescope whereas the light passing through the periphery passes through the normal IOL configuration. Overall diameter of the IOL is 13mm while the size of the optic is 6.5mm. The anterior, central mirror size is 1.4mm. The posterior mirror is doughnut shaped and 2.8mm in diameter with a central hole of 1.4 mm 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 & SiO2 (dielectric coatings) thus creating the mirror effect. The thickness of these mirrors is only 1-2 microns. The entire IOL is also coated with Parylene C (poly-para-xylyllenes) for the reasons of biocompatibility.

This LMI was designed to have 2.5X magnification, i.e. magnifying the central image on the retina 2.5 times. 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.

Surgery

Conventional phacoemulsification or 700 micron cataract surgery (Microphakonit), using this IOL, can be done. The corneal tunnel is then increased with a diamond knife or regular keratome to 6.5 mm and the IOL placed in the bag. (Figure 2) We have done seven cases till now and one patient was pseudophakic and in that case explantation of the existing IOL was performed followed by implantation of the new IOL. All the patients were found to have anterior chamber depth within normal range which was also assessed on the anterior segment OCT. The endothelial density was also not affected by the IOL. Post-op we observed improvements in distance visual acuity up to 6 months. The mean postoperative distance visual acuity at the end of 6 months was 0.133 as compared to 0.067 pre-op values. Fundus evaluation of all patients was done by the same retina specialist and it was found easy to do.

Summary

The LMI is similar to a usual IOL used after phacoemulsification and is fully placed in the bag in a similar way. It provides magnified central image up to 2.5 times the normal while maintaining the normal peripheral vision through the peripheral portion of the lens. There is no relative movement between the eyes and the IOL unlike an external telescope. It requires 6.5 mm corneal incision unlike more then 10mm in the case of the IMT thus reducing surgically induced astigmatism. In this study we found the post-op examination of these patients easier with only minimal glare problem due to inadvertent reflection from mirrors. This provides no difficulty for future retinal photocoagulation in contrast to IMT which is having limited possible fundus 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 quite small as compared to IMT.

Editors’ note: Dr. Agarwal has no financial interests related to his comments.

ABOUT THE AUTHOR

Professor Amar Agarwal, is director, Agarwal’s Eye Hospital, Chennai, India. He can be reached at 91-44-2811-6233 or dragarwal@vsnl.com.

LMI … a new mirror telescopic IOL LMI … a new mirror telescopic IOL
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