Printer Friendly

Intraocular magnifying devices for patients with macular degeneration.

This article will review currently available intraocular magnifying devices for patients with macular degeneration.

Optometrists [COMMUNICATION][OCULAR DISEASE]

Dispensing opticians [COMMUNICATION][LOW VISION]

1 CET POINT

Introduction

In an ever-ageing population, age-related macular degeneration (AMD) is the leading cause of irreversible blindness in the industrialised world. (1) As the number one cause of visual impairment among persons aged over 75 years, it is a great concern in public health. AMD can be classified into two groups: dry or non-exudative and wet or exudative. (2) In the case of exudative AMD, treatment options have been revolutionised over the past decade with the introduction of intravitreal injections of anti-vascular endothelial growth factor (anti-VEGF). (3) Radiation as a treatment modality for neovascular AMD is not a new concept. Local radiation therapies have been shown to prevent proliferation of vascular tissue via inhibition of neovascularisation. Following exposure to low-dose radiation, vascular endothelium undergoes morphologic and DNA changes, inhibition of replication, increased cell permeability, and ultimately apoptosis. In addition, the proliferation of fibroblasts and formation of fibrosis, often seen in end-stage neovascular AMD, is inhibited.

Recently, localised low-energy X-ray radiation therapy to the macula (external low dose radiotherapy, ORAYA Therapeutics, CA, USA) is also showing promising results as an alternative treatment for wet AMD. (4) While the treatment for exudative AMD is widely available, reduced near visual acuity is still a growing problem for patients with macular degeneration. A number of external magnifying devices are currently available for use but these have limited acceptance by some patients. (15) With this in mind, an increasing amount of focus has been placed on visual rehabilitation of these patients using innovative intraocular systems. (6) A variety of intraocular implants including intraocular telescopic systems and intraocular lenses (IOLs) have recently become available. This article will review these in turn.

Implantable miniature telescope (IMT)

The implantable miniature telescope (IMT) is a fixed focus, Galilean design, telescopic prosthesis designed for monocular implantation (see Figure 7). (1) Monocular implantation allows the fellow eye to be used to provide peripheral vision for orientation. The IMT allows magnification of up to 3x, projected over an area of 55[degrees] of peripheral and central retina with a focal distance of 50cm. (2,7) Approved by the US Food and Drug Administration (FDA) in July 2010, the IMT was the first intraocular magnifying device approved for end stage AMD. (1)

The IMT is placed within the capsular bag following cataract surgery and protrudes forward into the anterior chamber. (5,8) The front of the IMT sits approximately 2mm behind the posterior surface of the cornea. (2) Implantation of the device is more difficult than standard cataract surgery and has the drawback of requiring a large limbal incision of around 12mm and a capsulorhexis of greater than 7mm.

Patients for IMT require a pre-operative best corrected visual acuity (BCVA) of between 6/48 and 6/240 and demonstrate a visual improvement of five lines with the use of an external telescope and a self-illuminated near ETDRS chart. (5) The device is designed for optimised intermediate viewing to allow patients to recognise images using natural eye movements. However, IMT can be used for any viewing distance with the use of spectacles. (5)

As with any telescopic device, the patient will experience a restriction in the field of view of around 22-25[degrees] for the IMT device. (5) Driving with the implant is considered a contraindication due to aniseikonia. The image of the implanted eye will be 3x larger than that of the fellow eye causing difficulty with depth perception. (5)

A potential risk of the procedure is corneal endothelial cell loss, affecting overall corneal health, (9) although studies have shown that the cell loss is comparable to any large incision cataract surgery. (5) Long term follow up indicates that the cell loss is due to the surgical procedure and not as a result of continuous damage. Further, improvements in surgical technique reduce endothelial cell loss. (5)

Lipschitz macular implant (LMI)

The Lipschitz macular implant (LMI) is an IOL, which uses the Cassegrain telescopic design with two miniature mirrors that magnify the image on the retina. (5) The implant works on the principle of a dual optical system. The 2.8mm posterior mirror contains a 1.4mm optically clear central zone allowing the central rays to pass through and focuses the light on to the 1.4mm anterior, retinal-facing mirror resulting in magnification of the image. The peripheral rays are unaffected allowing for magnification while maintaining good peripheral vision. (8) The LMI has been designed to give approximately 2.5x magnification, (5) with an overall diameter of 13mm with a central optic of 6.5mm. The mirror effect is created using coats of multiple layers of titanium oxide and silicon dioxide (dielectric coatings). To enhance the biocompatibility of the IOL, polyparaxylylenes are used. (5) Implantation requires a limbal incision of 6.5mm with the device placed in the capsular bag.

In 2008, a prospective nonrandomised pilot feasibility clinical trial on the use of the LMI was carried out on six eyes of six patients. (1) The results showed no intraoperative complications and at six months there was no reduction in distance visual acuity. Examination of the fundus was unchanged following the implantation of the LMI. A post-operative subjective questionnaire survey showed a significant improvement in quality of life with patients finding it easier to read large print, count money and move independently after surgery.

iolAMD

The iolAMD lens system was given CE mark approval in 2004. It works on the principle of a Galilean telescope, whereby two hydrophobic acrylic IOLs are injected into the capsular bag and the sulcus, respectively (see Figure 2). (1) The IOL placed in the capsular bag is a high power minus lens of -49D; this implant has a 4mm central optic and an overall diameter of 11mm. The second IOL, which is placed in the ciliary sulcus, is a high power plus lens of +63D and is a slightly decentered 5mm hyperaspheric optic with a 12mm diameter. This pairing of lenses is designed to give a theoretical magnification of 1.25x to 1.3x magnification. (3)

For implantation of the iolAMD, a 5mm capsulorhexis with a 2.8mm limbal incision is required. Intraoperatively following cataract extraction, the high minus IOL implant is injected in to the capsular bag, after which the second IOL is injected and positioned in the sulcus. (1)

An interventional, noncomparative prospective single-centre pilot study was published in 2015. (1) For inclusion in the study patients required best corrected distance visual acuity of less than 0.25 decimal (6/24) and had to show an improvement while using a simulated telescopic IOL; this was done with the use of a handheld extraocular magnifier with a built in prism. Exclusion criteria included: active wet AMD; phacodonesis; corneal guttata; axial length of greater than 24.5mm and less than 20.5mm; history of angle closure glaucoma; retinal detachment; optic neuropathy; and intraoperative surgery within the last six months.

At the final postoperative review, a 67% overall increase in the mean corrected distance visual acuity (CDVA) and 50% overall increase in the mean corrected near visual acuity (CNVA) was recorded. These results exceeded the pre-operative expectations, which came from a simulator. Refractive outcomes in the study were noted to be relatively predictable with a mean spherical equivalent of -1.50D and induced astigmatism of 0.50D being recorded. (1)

Following the success of the iolAMD, the London eye hospital has recently developed a new single, injectable, soft acrylic intraocular lens for implantation, iolAMD Eyemax Mono (see Figure 2). Based on the original Galilean telescope design, this lens creates a focused image on retinal areas extending 10 degrees from the fovea thus allowing patients to use a multiple PRLs (preferred retinal locus).

This lens design allows up to 30% magnification, maintaining optimised vision as the disease progresses. At the time of this article there are currently no peer reviewed scientific papers available.

Scharioth macula lens (SML)

The Scharioth macula lens (SML) is an add-on, that is to say, a piggyback IOL, which can be placed in the ciliary sulcus of pseudophakic eyes; this device is currently CE marked but does not have FDA approval. The IOL has an overall diameter of 13mm with a central optic zone of 1.5mm. The central optic zone has an add of +10.00D and the remaining optic zone is refractively neutral (see Figure 3).6 A theoretical magnification of 2x can be achieved but this is dependent upon ocular anatomy and final reading distance.

Unlike other intraocular devices for AMD procedures, the SML can be implanted simultaneously during uncomplicated cataract surgery. However, it is recommended that this is done as a second -stage procedure following cataract surgery. As the name implies, the lens is an add-on IOL, therefore explantation of the primary/original monofocal IOL (implanted during cataract surgery) from the capsular bag is not required. A minimum limbal incision size of 2.2mm is required and this IOL is injected with a custom designed injector in to the ciliary sulcus space. The smaller incision required compared to that of an implantable telescope (6.5mm) reduces the risk of surgically induced astigmatism. The SML is designed for use with patients with dry AMD but may be useful for patients with other macular disease, such as diabetic maculopathy. The SML is implanted monocularly in the patient's best eye. (6) For best results patients should have distance visual acuity of less than 0.4 decimal (~6/15) and equal to or more than 0.1 (~6/60). Pre-operative assessment includes measuring near visual acuity using a self-illuminated ETDRS near vision chart with a +2.50 addition at 40cm and again with a +6.00 addition at 15cm. An improvement in near visual acuity of three lines or more indicates suitability for implantation of the SML.

The inventor, Gabor Scharioth, published the proof of concept for the SML in 2015. (6) A pilot study involved eight eyes of eight patients who had the device implanted monocularly in their best eye. Visual acuity was measured at four weeks postoperatively where in all but one case there was an improvement in CNVA. Preoperative measurements of near visual acuity using +2.50D addition at 40cm and a +6.00D addition at 15cm were measured and were compared to postoperative results. An improvement of 4.4 lines with the SML at 15cm compared to the +2.50D addition at 40cm was recorded and an improvement of 2.1 lines with the device at 15cm versus the +6.00D addition at 15cm. Patients unsuitable for this type of IOL include eyes requiring complicated cataract surgery, excessive zonular weakness, chronic uveitis, active rubeosis iridis, and central corneal opacities.

The main advantage of the SML is its ease of use, reversibility and opportunity to use this implant in previously pseudophakic eyes. The design of the Scharioth lens does not limit visual field unlike other telescopic IOL systems, therefore, there is no contraindication for the use of this IOL in single-eyed patients. Based on the initial proof of concept publication, a prospective multicentre European trial involving seven clinical centres in six countries is currently underway to prospectively evaluate the medium to long-term visual outcomes of this IOL.

The interim (at three months) results on 35 eyes of 35 patients in this trial was recently presented at the European Society of Cataract and Refractive Surgery meeting in Copenhagen 2016, (10) and at the annual meeting of the American Academy of Ophthalmology in Chicago in October 2016. (11) In all 35 subjects the near visual acuity showed a median improvement from 0.24 decimal (6/24) to 0.63 decimal (6/9.5) postoperatively, without comprising on the distance visual acuity. The IOL had to be explanted in two patients due to excessive postoperative glare.

Conclusion

The visual rehabilitation of patients with dry AMD had been restricted in the past to use of supplementary magnifying devices. With advances in optics and intraocular lens designs there is now a choice of devices that can visually rehabilitate patients with dry AMD and provide useful near vision and improve quality of life for these patients. O

Exam questions and references

Under the enhanced CET rules of the GOC, MCQs for this exam appear online at www.optometry.co.uk. Please complete online by midnight on 9 June 2017. You will be unable to submit exams after this date. Please note, the MCQs may require practitioners to apply additional knowledge that has not been covered in the related CET article. CET points will be uploaded to the GOC within 10 working days. Visit www.optometry.co.uk to view the article and accompanying 'references' in full.

Course code: C-55754 Deadline: 9 June 2017

Learning objectives

* Be able to explain to patients about the latest options in intraocular magnifying devices (Group 1.2.4)

* Be able to identify patients with macular degeneration that may be suitable for intraocular magnifying devices (Group 6.1.9)

* Be able to explain to patients about the latest options in intraocular magnifying devices (Group 1.2.4)

* Adopt a multidisciplinary approach in the management of patients with macular degeneration (Group 6.4.2)

Emma Robb MCOptom, DipTp(IP) and Sathish Srinivasan FRCSEd, FRCOphth, FACS

* Emma Robb is a full time practising optometrist in Scotland. She qualified from Glasgow Caledonian University in 2012 and completed her independent prescribing training in 2015.

* Sathish Srinivasan is a consultant ophthalmic surgeon and joint clinical director at University Hospital Ayr, and medical director at Ayrshire Eye Clinic and Laser Centre. He specialises in corneal, cataract and laser refractive surgery.

Caption: Figure 1 Implantable miniature telescope

Caption: Figure 2 The iolAMD Eyemax Mono

Caption: Figure 3 The Scharioth macula lens
COPYRIGHT 2017 Ten Alps Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2017 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Author:Robb, Emma; Srinivasan, Sathish
Publication:Optometry Today
Date:May 1, 2017
Words:2293
Previous Article:The ABC of sight impairment registration.
Next Article:Homonymous hemianopia following stroke: visual field remediation.
Topics:

Terms of use | Privacy policy | Copyright © 2021 Farlex, Inc. | Feedback | For webmasters |