Understanding telescopic lens implant surgery

What is a telescopic lens?
How does a telescopic lens system work?
Which telescopic lens implant will work for you?
The traditional IOL VIP system?
The new IOL VIP Revolution?
The implantable Miniature Telescope (IMT)
Does the system work like a magnifying glass?
Does the telescopic lens correct distance vision without glasses?
Will the telescopic lens be right for you?
What happens if you have already had cataract surgery?
What is the alternative to telescopic lens surgery?

 

What is a telescopic lens?

The term telescopic lens refers to an implant system inserted into the eye following cataract extraction. Several systems have now been developed, specifically to improve central vision in patients with macular disease.

In standard cataract extraction, known as phacoemulsification, the opaque natural lens of the eye is replaced with a single clear plastic lens. In a telescopic lens procedure a more complex system is implanted, the telescope being comprised of either a combination of mirrors, or a combination of lenses. Only the lens-based telescopes will be discussed here, the implant working just like a ship's telescope with 2 lenses inserted either separately, or contained within a single tube.

It is helpful to know a little about the eye and how it works in order to understand the telescopic lens system.

The cornea forms the clear window into the eye. The iris, which is the coloured part of the eye with the black pupil in the middle, lies behind the cornea. The lens lies behind the iris.

Anatomy of a normal eye

The wall of the eye is formed by three layers, the retina, the choroid and the sclera.

The cornea forms the clear window into the eye. The iris, which is the coloured part of the eye with the black pupil in the middle, lies behind the cornea. The lens lies behind the iris.

The retina is the light-sensitive nerve tissue that lines the inner wall of the eye. Rays of light enter the eye, passing through the cornea, pupil and lens before focusing on to the retina. The retina contains photoreceptors which convert light into electrical impulses. In the healthy eye these impulses are sent via the optic nerve to the brain, where sight is interpreted as clear, bright, colourful images. The retina can be likened to photographic film in a camera.

The macula is a small area at the centre of the retina. It is very important as it is responsible for our central vision. It allows us to see fine detail for activities such as reading, recognising faces, watching television and driving. It also enables us to see colour.

The choroid is the underlying vascular (blood vessel) layer of the eye from which the retina receives oxygen and nutrients.

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How does a telescopic lens system work?

There are a number of lens-based telescopic systems on the market. They look rather different, but all work in the same way using two lenses to produce a magnified image. The choice of telescope is guided by the degree of visual loss, those with moderate visual impairment usually doing best with a low power telescope and those with more severe visual impairment being guided towards a high power telescope.

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Which telescopic lens implant system will work for you?

All telescopic systems are low power compared with, for example, a standard pair of binoculars. The price we pay for a larger central image is loss of the peripheral visual field which, in its self, can cause significant visual impairment. Patients who still retain moderate levels of vision (for example being able to read about half of the opticians’ chart) will probably do best with a low power system which, when appropriate, can be implanted into both eyes. Patients with more severe visual loss (those who have lost the ability to see all letters on an opticians’ chart) will do better with a high power telescopic system. The high power telescope is only ever implanted into one eye, the better of the two being selected.

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The Traditional IOL VIP system

The IOL VIP (intra-ocular lens for visually impaired persons) is a twin lens system which has been widely available for several years. The traditional implants have recently been modified to give us the IOL VIP Revolution. For a majority of patients the IOL VIP Revolution is the system of choice but, for technical reasons, there are occasions when the traditional IOL VIP may still be preferred, for example when the subject has already undergone cataract extraction with implantation of a standard lens.

The lens behind the iris is a minifying glass (thick at the edges). The lens in front of the iris is a magnifying glass (thick in the middle).

There are two ways in which the implant lenses may be of benefit:
1. The two lenses can operate as a miniature telescope, magnifying the image at the macula. This is the principal effect of the lens system.
2. The alignment of the lenses can be rotated to divert the image toward a less damaged area of the macula. This is a secondary effect which, in some subjects, may be irrelevant.

The telescopic lens is designed to produce relatively low-level magnification of around thirty per cent. Macular disease limits vision by producing a blind spot or an area of impaired vision. The effect of the IOL VIP system is to enlarge the image around the blind spot, making the central area of impairment less intrusive.

In some patients the IOL VIP may be more effective when an area just away from the macula is used as the point of visual fixation. In other words, the patient may choose to look just “off centre” to get the best possible picture. If appropriate we will lend you a laptop computer with visual exercises, to help you learn to fixate on a new point and achieve your best visual potential.

The New IOL VIP Revolution

The principle is exactly the same as the standard IOL VIP in that two lenses are inserted but, in this case, both are placed in the capsular SALring. Again, the deeper lens is a minifier and the more forward lens a magnifier. Before inserting the lens however, a plastic ring is injected into the capsular bag to provide support. The ring has a grove on its inner surface into which the supporting feet of the two Revolution lenses will sit. By stabilising the peripheral feet of these lenses the deeper lens will push backwards, and the more forward lens push forwards as intended maintaining the separation between the two and giving good telescopic effect. When ordering the IOL VIP Revolution we have a choice between lenses with a prismatic effect (helping to move the image off centre as is the case with the traditional IOL VIP) or with lenses which sit aligned on the line of vision. Avoiding the insertion of an anterior chamber lens (the lens in front of the iris) reduces some of the risks of surgery and the system seems to give more consistent and slightly more powerful levels of magnification. As with the traditional system the IOL VIP Revolution requires adaptation and some patients will benefit from computer reading exercises to pick out the best point of central vision.

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The Implantable Miniature Telescope (IMT)

This is a much more powerful telescope, magnifying between two and three times (100 to 200%) depending upon the size of the eye. The two lenses are contained in a tiny tube, which is its self-mounted in a circular disc. This disc is opaque (to prevent stray light entering the eye) and is inserted into the capsular bag, just like a standard lens. The IMT is however, much bigger than a standard implant requiring a large incision in the cornea and multiple sutures to close the wound.

The benefit of higher magnification is obvious to most subjects, the object in view magnifying to more than twice the size. The price we pay for this system is that considerable peripheral vision is lost, such that using the operated eye alone it would be not be possible to walk safely across a room. For this reason the IMT implant is only ever used in one eye (the better of the two) the fellow eye remaining as a “navigation eye” giving sufficient peripheral vision to allow a subject to move around comfortably without risk. In effect, the non-operated eye is used for getting around and the operated eye gives more detailed central vision, whether for near or distance.

If the IMT is the chosen lens then we have to be sure that you can cope with the loss of peripheral vision from the operated eye. To do this we ask you to wear a pad over the eye at home to ensure that you can move around safely using only peripheral vision from the non-operated eye.

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Do the systems work like a magnifying glass?

No. A magnifying glass only produces a larger image when an object is held close to the eye. The telescopic lens procedure produces a larger image at looking through weak binoculars.

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Does the telescopic lens correct distance vision without glasses, as is often the case for modern cataract surgery?

The standard lenses used in cataract surgery come in a variety of powers such that, after careful measurement of the eye, long or short sightedness can often be corrected. This is not the case with telescopic lenses. The IMT is available only in a single power and, although the IOL VIP can be ordered to minimise the need for spectacle correction, you should assume that glasses may be required for both near and distance with any telescopic system.

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Will the telescopic lens be right for you?

Even if you have previously been told that “nothing can be done” for your eye condition, a telescopic lens may help improve your central vision.

Implantation of the telescopic lens will only be performed when your macular degeneration has been assessed as stable and wet disease, if present, has been controlled.

As part of the outpatient assessment a special simulator can be used to test the potential improvement in vision.
Through this, the world appears larger and objects come closer.

The simulator demonstrates the effect of the telescopic lens, allowing you to experience the potential enhancement before proceeding with surgery.

If the simulator is of benefit when testing in clinic, it is highly likely that the surgical procedure will produce an effect at least as good, if not better. There are different simulators for the IOL VIP and the IMT. We will guide you towards the appropriate choice.

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What happens if you have already had cataract surgery?

The IMT can be inserted following removal of a standard cataract implant lens. It may be possible to use the IOL VIP system, but only the more traditional format in most cases.

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What is the alternative to telescopic surgery?

For some patients cataract surgery alone may improve illumination of the retina and help with everyday tasks.

It is important not to forget the potential benefits of standard low vision aids (LVAs) from your local ophthalmic unit or specialist optometrist.

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