Understanding CK treatment

What is conductive keratoplasty?
How does CK correct your sight?
Will CK give you perfect reading vision?
Will the effect of CK last forever?
Why do we like CK?

 

What is conductive keratoplasty?

Conductive keratoplasty is a procedure for the correction of presbyopia. In CK, a probe is used to deliver high frequency radio waves into precise spots on the cornea, causing a change in shape and thus focusing power.

It is helpful to know a little about the eye and how it works in order to understand how CK can be used to treat presbyopia.

Anatomy of a normal eye

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, is behind the cornea. The lens lies behind the iris.

In a healthy eye the lens is clear and able to focus light on to the retina, the light-sensitive nerve layer that lines the inside of the eye.

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

The choroid is the underlying vascular (blood vessel) layer of the eye, from which the retina receives oxygen and nutrients. The sclera or “white of the eye” forms a tough protective coat.

The retina sends signals via the optic nerve to the brain where sight is interpreted. This process can be likened to the lens in a camera focusing light on to photographic film, from which images can be developed.

The focusing of light by the eye depends on three main factors; the power of the cornea, the power of the lens inside the eye and the length of the eye. The cornea and lens work together to create a focused image on the retina, the length of the eye being fixed.

In short-sight (myopia) the eye is “too big” and the clear image falls in front of the retina.

 

In long-sight (hyperopia or hypermetropia) the eye is “too small” and the clear image would fall behind the retina.

In a normally-sighted eye, a healthy young lens has the ability to adjust the eye’s focus, letting us see things clearly both near and far away. When we read, a circular muscle around the lens contracts, allowing the lens to change shape and achieve near focusing – this process is known as accommodation. Many people begin to lose this ability when they reach middle age, finding for the first time that they need a spectacle correction for reading; this is called presbyopia.

In presbyopia, when trying to perform close work, the inability of the lens to adjust means that the point of focus falls “behind” the retina, therefore a clear image cannot be seen.

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How does CK correct your sight?

CK uses radio waves to reshape the cornea. A tiny probe (as thin as a human hair) is used to create eight small spots in a circular pattern on the surface of the cornea.

The passage of the radio waves through the corneal tissue causes these spots to shrink, which in turn changes the shape of the cornea. This gives it a greater lens effect, increasing the refractive power of the eye and bringing near vision naturally into focus.

Changed corneal curvature

The treated eye is, in effect, rendered slightly short-sighted, whilst the fellow eye retains good distance vision. Most people are completely unaware that one eye has been set for distance and one for near, binocular vision allowing the two eyes to work together effectively.

The slight loss of distance vision in the treated eye is of no functional consequence, although this will be checked carefully before CK using lenses to simulate the effect of mixed focal lengths.

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Will CK give you perfect reading vision?

 

The aim of CK is to allow everyday tasks to be performed without total reliance on reading spectacles for all near visual tasks.

Successful CK will allow you to use a computer, read large newsprint and perform everyday tasks such as reading a menu, viewing a mobile phone or looking at prices on a supermarket shelf.

CK is not designed to allow prolonged reading of fine print in dim illumination. For this, reading glasses will still be required.

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Will the effect of CK last forever?

No. In time the functional benefit of CK will wear off. Not necessarily because the corneal changes reverse, but simply because the loss of normal accommodation, both in the treated and fellow eye, will continue with age.

It is common for CK to be repeated after a few years and ultimately more definitive surgery, such as refractive lens exchange, will be required.

CK is designed as a safe, quick and minimally invasive treatment, but not as a permanent cure for a progressive ageing change.

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Why do we like CK?

CK is popular because it is a minimally invasive treatment. The probe used to create the eight CK spots on the cornea does not penetrate the cornea and thus there is no chance of inducing infection within the eye. It is this tiny risk of induced infection (endophthalmitis) which, sadly, will always be present in procedures such as refractive lens exchange.

A second safety advantage of CK is that the centre of the cornea is not touched. The eight spots are performed in a circle in the mid-periphery of the cornea, most commonly at a diameter of seven millimetres. This is well away from the visual axis of the eye and does not therefore produce some of the troublesome effects associated with other refractive techniques.

Similarly, the minimalist approach to CK is not known to upset the surface of the eye or the tear film and is therefore much less prone to inducing dry eye symptoms.

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