Intraocular telescopes for macular degeneration: course code C-15909 O/D.
A number of treatments are available or are being developed for the treatment of neovascular ('wet') AMD, including intra-vitreal anti-vascular endothelial growth factor (anti-VEGF) injections. However, wet AMD only constitutes 10-15% of cases of AMD. In contrast 'dry' AMD constitutes 85-90% with limited treatment options available; (5) most notably, this typically involves advice on increased dietary intake of anti-oxidants through healthy eating and supplementation with lutein- and zeaxanthin-containing vitamins, and protection of the eyes from ultraviolet (UV) and blue-light radiation with sunglasses. Those of you familiar with low visual aid clinics will attest to the frustration and despair that patients with dry AMD experience in an attempt to regain their reading and navigation ability. Therefore, it is fitting that intraocular telescope implantation offers a promising hope for the future.
Intraocular telescopes are most commonly based on the Galilean telescopic system (Figure 1), whereby a high minus powered bi-concave eye piece lens is combined with a high positive powered bi-convex objective lens, to produce a magnified, erect, virtual image. Magnification of such systems approximates to the dioptric ratio of the eye piece lens to the objective lens. In the Implantable Miniature Telescope (IMT) the magnification is between 2.2x and 3x. (6) The Intraocular Lens for Visually Impaired Persons (IOLVIP) has a magnification of 1.3x with "a small prismatic effect due to misalignment (planned) of the IOLs". (7)
Once a patient receives an intraocular telescope implant, the post-operative refraction is influenced by the separation of the two lenses. This is fixed in the IMT system and in the IOLVIP system, particularly in hyperopes, this can give rise to high (5.007.00DS) degrees of residual hyperopia.
The IMT (Figure 2) consists of a quartz tube that houses two wide angle micro-lenses. The diameter of the IMT is 3.6mm and the length is 4.4mm with a carrier haptic of 13.5mm diameter. The IMT recently completed a two-year trial study that included 28 centres, (6) and has received FDA approval. In this study, 206 patients were enrolled and 174 were analysed at two years after implantation. The study mandated the IMT to be implanted in the worse eye of the patient and it was found that the best-corrected visual acuity (VA) improved by three lines (doubling of the visual angle) in over 60% of patients, and by 5 lines of acuity in nearly 20% of patients.
There were initial concerns from ophthalmologists about corneal endothelial cell loss, and this was reported to be 25% cell loss at one year following implantation. However, this cell loss does not appear to be cumulative with only 2.4% additional loss reported between years 1 and 2. (6) This endothelial cell loss is largely due to the wide incision required for implantation; it is much longer than an incision made for phacoemulsification cataract extraction (2.8mm) or an extracapsular cataract extraction (7-10mm).
By necessity, this system causes a restriction in visual field of about 25% loss. As such, at present it is recommended that the IMT only be used in the worst eye of a patient, in order to enhance reading ability. The better eye is left as a navigational eye.
The IMT is currently completing mandatory "pre-marketing" assessment and the author has been invited to collaborate with the FDA and the manufacturers when introducing the IMT to the UK in 2011. Further outcomes data will also, hopefully, be obtained and published in the future, but it is already clear that the outcomes with the IMT look very promising.
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The IOLVIP typically comprises lenses of power +53D as the anterior optic and -64D as the posterior optic. It is a lower magnification system than the IMT but incorporates a "prismatic" effect, thereby diverting the image onto a preferred retinal locus (PRL), which is a point on the retina that is away from a macular area affected by AMD (Figure 3).
Pre-operatively the PRL is determined using a simulator (Figure 4), which allows an assessment of the likely visual improvement that will be obtained. In the IOLVIP system, the prismatic simulator is placed in a trial frame over the optimal distance vision refraction. The simulator is rotated to determine the point at which visual improvement is maximal. This tells the surgeon which way to orientate the IOLs during the operation.
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The author introduced implantation of the IOLVIP in the UK in 2007 and at six months noted that 89% of patients had doubled their distance vision (preoperative distance VA was logMAR 1.52 whilst post-operative distance VA was logMAR 0.69) (Figure 5). (8) In addition, the visual outcomes predicted by the simulator closely reflected the actual visual outcome. Indeed, in some patients the outcomes were better than predicted by the simulator, because of extraction of the lens opacity at the time of surgery. This predictability of outcome carries many benefits. Principally, the patient and the surgeon can determine with substantial confidence the likely outcome prior to surgery, whilst also giving the patient and their family a realistic prognosis.
The outcomes observed by the author in his own work are similar to the outcomes observed elsewhere. In the Milan study group (7) the pre-operative distance VA was logMAR 1.30 whilst post-operatively this improved to logMAR 0.72. In the Valencia study group (9) the pre-operative distance VA was reported to be logMAR 1.37 and this improved post-operatively to logMAR 0.68. Longer term follow-up at 18 months post-operatively has revealed that in some patients the initial improvement in VA was lost, due to advancement of AMD and corneal decompensation. (10) Indeed, this highlights the importance of making all patients aware of the risks and that there is no guarantee of a long-term, sustainable improvement in VA. Furthermore, it is important to counsel patients and communicate to them and their families that surgery does not prevent AMD, it merely compensates for it for a period of time. Otherwise, it can be distressing for these patients if at a later stage they find that their initial improvement in vision has declined thereafter. It is also important to clarify to patients that there will be substantial induced hyperopia post-operatively; indeed, the research reported above has clearly noted misgivings about post-operative hyperopia within patient groups. (7,8,910)
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Note that it is important to assess visual function in terms of logMAR acuity as opposed to traditional Snellen acuity, due to design flaws in the latter that may over-estimate true VA. Indeed, logMAR charts such as the Bailey-Lovie chart are advantageous in that task difficulty remains consistent across all levels of acuity, with equal number of optotypes presented per line, and there is a regular logarithmic progression of acuity such that each line is a scaled version of the preceding line, allowing each individual letter to contribute to the VA measure, increasing the accuracy.
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The IOLVIP and IMT have CE marks and are supported by NICE Guidelines (IPG 272). Only the IMT has FDA approval. Although the telescopes are CE marked and have NICE guidelines with regard to audit, funding for surgery on the NHS is unpredictable. The author has been successful on many occasions in presenting patients to their Primary Care Trusts as "special circumstances". Indeed, lately the approval for NHS funded surgery has become rare. Interestingly, it is likely that the IMT may be approved by Medicare in the USA, which perhaps indicates a more sympathetic appreciation of the enhanced quality of life that the device offers.
Top ten tips
Patients that may be deemed suitable for implantation of intraocular telescopes have a lot to gain by undergoing the procedure. It is important however to consider the following factors and advice, in order to optimise the possible outcomes:
1) Patient selection is all important. It is the author's experience that visual outcomes are dependent on the extent of AMD. As a rule of thumb, good outcomes can only be expected with less than 2 disc diameters (DD) of AMD (Figure 6).
2) Patients need to be highly motivated with a clearly defined PRL for eccentric fixation.
3) This procedure does not have a "wow" factor, and it is important not to mislead patients to expect an outcome that is akin to the change people may experience following routine cataract extraction or corneal laser refractive surgery for refractive error correction. Visual improvement can be slow and needs encouragement.
4) Some patients with moderate AMD alongside cataract may benefit from cataract extraction alone. However, cataract surgery in advanced AMD is generally of limited value.
5) Optometric input is vital in helping with patient selection and postoperative refraction. In general terms, the author advises patients to have separate distance and reading glasses for one year post-operatively. Ancillary devices eg, Eschenbach magnifiers, can still be used if required. The author works in conjunction with an experienced low vision aid optometrist in his clinics to ensure optimal postoperative visual function can be gained.
6) Patients need to be counselled carefully about visual expectations. The author generally only discusses surgery with patients who show at least 3 lines improvement with a simulator. Advising patients that their AMD is too far advanced for surgery can often be met with great dismay and requires sympathetic counselling.
7) Great dismay can be encountered when vision improves for a time and then regresses due to advancement of AMD, after surgery. It is important for the surgeon to emphasise that the surgery does not delay the advancement of AMD but it merely reduces its visual impact for an unpredictable period of time.
8) Both IOLVIP and IMT telescopic systems have a rehabilitation programme that is directed by the surgeon/ optometrist. The author finds these of limited value since if a patient has well established eccentric fixation they do not need to be taught how to utilise it; for those that do not eccentrically fixate, the rehabilitation program may be of some use though.
9) The family input is vital. The author usually insists on as many family members being present at the assessment and follow-up appointments as possible. They can see the visual improvement afforded by the simulator and thereby aid counselling of the patient about the expected visual outcomes. Indeed, they can avoid the patient getting "carried away" with perceptions of "miracles". 10) Surgeons and optometrists need to advise patients with honesty and integrity. These patients may have had a harrowing time in the past and surgery is a "last chance saloon" for many. They need careful selection and counselling.
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Two new 'telescopic' systems are currently undergoing trials for improving visual function in AMD and the outcomes of these are awaited in anticipation. The Lipshitz Macular Implant (LMI) uses a Cassegrain (Newtonian) telescopic system and magnifies the central image using a concave mirror system. The Nu-lens system is a sulcus fixated IOL that can reportedly provide 10-14D of accommodation. It was originally designed for use in cataract surgery for the correction of presbyopia, but it has clear possibilities for use in patients with AMD too.
We all eagerly await the potential improvements afforded by gene therapy and stem cell therapy too. While much research in this field shows great promise, we may have to wait many more years yet before this becomes a distinct clinical treatment option. References
See http://www.optometry.co.uk/ clinical/index. Click on the article title and then download "references."
PLEASE NOTE There is only one correct answer. All CET is now FREE. Enter online. Please complete online by midnight on April 22 2011--You will be unable to submit exams after this date--answers to the module will be published on www.optometry.co.uk. CET points for these exams will be uploaded to Vantage on May 2 2011 .
Course code: C-15909 O/D
1. Which of the following statements about intraocular telescopes is TRUE?
a) They are an alternative to anti-VEGF treatment
b) They produce a magnified, erect image
c) They use a Newtonian telescopic system
d) They are suitable for most cases of AMD
2. Which of the following statements about the Implantable Miniature Telescope (IMT) is TRUE?
a) It incorporates a prism
b) It is suitable for the better eye
c) It magnifies by between 2.2x and 3x
d) It can cause progressive corneal epithelial cell loss
3. Which of the following statements about the IOLVIP is TRUE?
a) It incorporates a 3x magnification with a prismatic effect
b) It has FDA approval
c) It induces hyperopia
d) It is as effective as cataract surgery in advanced AMD
4. Favourable outcomes with the use of intraocular telescopes may be seen with which of the following?
b) Less than 1 disc diameter of AMD
c) Recent onset dry AMD
d) Unilateral cases of AMD
5. Which of the following statements about post-operative rehabilitation is TRUE?
a) It is essential in all cases
b) It is of great value in advanced disease
c) It is often not necessary in patients with well established eccentric fixation
d) It requires continued monitoring
6. Which of the following statements about intraocular telescope surgery is TRUE?
a) It causes advancement of AMD
b) It can delay AMD
c) It has no effect on progress of AMD
d) It induces glaucoma
About the author
Brendan Moriarty trained in medicine at the Middlesex Hospital in London and gained his FRCS in 1984. He then worked as fellow and medical director for Project Orbis, the internationally renowned flying eye hospital. He became Fellow in glaucoma at Moorfields Eye Hospital in 1987 and he is now head of glaucoma at Leighton Hospital, Crewe. His expertise in intraocular telescope surgery has been recognised by his role as Special Advisor to NICE. He was awarded "Best Original Work" by the American Academy in 2008. He consults privately at The Prospect Eye Clinic in Altrincham but does not accept paid consultancies with industry; his fees have been donated to the Save the Children Fund. He has no financial interests in the products discussed. Visit www.prospecteyeclinic.com for more information about ophthalmic techniques and procedures.
Brendan J Moriarty MA(Cantab), MBBChir. FRCS, FRCOphth, MD.
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|Title Annotation:||CET: CONTINUING EDUCATION & TRAINING|
|Author:||Moriarty, Brendan J.|
|Date:||Mar 25, 2011|
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