GB2498345A

GB2498345A - A spectacle lens with a prism for relieving myopia

Info

Publication number: GB2498345A
Application number: GB1200308.3A
Authority: GB
Inventors: Geraint William Griffiths; Mark Houlford
Original assignee: SVUK Ltd
Current assignee: SVUK Ltd
Priority date: 2012-01-10
Filing date: 2012-01-10
Publication date: 2013-07-17
Also published as: WO2014060713A2; WO2014060713A3; GB201200308D0

Abstract

An ophthalmic varifocal lens can incorporate a prism in four base specified directions (in, out, up, down) and vary the amount, direction and rate of change of prism between top and bottom sectors of the lens. This provides a prism controlled varifocal spectacle lens, which when glazed as spectacles looks like an ordinary pair of single vision lenses. The lenses prescribed in pairs allow differential control of the direction of prism at distance and near. They are designed to relieve the forces of the intra and extra ocular muscles on the globe, caused by the effort of maintaining binocular vision in eyes with a fixation disparity between them. These forces especially in the predisposed (young or nutritionally deprived) can cause myopia or symptoms associated with muscle imbalance. The lens can help to prevent myopia, relive associated symptoms and prevent manifest myopia getting worse.

Description

The Myolens A varifocal or single vision ophthalmic spectacle lens for the control and prevention of myopia (short sight)

Description

The Ivlyolens in appearance to a casual observer, will look like an ordinary lens when glazed into spectacles. The more experienced observer will see that the lenses in the spectacles may be a varifocal, where the relative positive power increases down the lens.

The most informed observer will be able to tell by observation or measurement that the horizontal prismatic effect in one or both lenses changes from top to bottom. This effect would be greater than produced purely by a decrease in the inter-pupiliary distance when the eyes converge to read. These lenses could be single vision or varifocal. This technology is different to prism-controlled bifocals, which split the top and bottom half of the lenses with a visible or blended line.

The prismatic effect could be base in or out or neutral in the distance parts of the lenses and similarly the near vision part could be base in or out or neutral, but the prismatic effect in the near vision part would vary independently from the prismatic effect in the distance part. The vertical prismatic effect may change from top to bottom. Horizontal and/or vertical prism could be different in each eye

Background

The purpose of the lens design is to relieve the mechanical stresses on each globe (eye) caused by a powerful cortical desire to maintain binocular single vision. In nature the survival of a hunter-gatherer species like homo-sapiens, would be severely compromised by double vision.

It is proposed that the forces in the intra-(cilliary) and extra-ocular muscles applied to the globe to maintain a clear focus and binocular single vision (fusion) can distort a growing eye (especially if already compromised by nutritional deficit and a softening globe {sclera}). This can lead to changes in shape or size of the globe resulting in refractive problems (short sight, astigmatism and anisometropia) The intention of the Myolens is to reduce these effects and relieve the symptoms that can arise from binocular imbalance. It is possible that when signs of ocular stress are seen (including incipient myopia) that the use of the Myolens will reverse the tendency for the myopia to develop. The need for the prism and the direction in which it is prescribed (given by the base or thickest edge of the lens) is decided by measuring fixation disparity (associated phoria) at various distances. The effect of the correction can be measured using a rate of character recognition test (CRST, comparative rate of reading test) at high and low contrast with two font types (Times {serif, high contrast} and Gill Sans {non serif, low contrast}) The need to understand the aetiology of myopia is particularly relevant in the 21st century because of the explosion in very recent times of computer use and extended periods of close work to which humans seem yet to adapt. The need to co-ordinate the eyes at a distance was essential for survival but it is only quite recently that survival (or at least a reasonable standard of living) began to be dependant on the same binocular skill applied at close distances. The difference arises from the need to converge the eyes, to maintain fusion, when regarding objects at close distances using a prehistoric visual system, which evolved to give clear comfortable vision primarily at longer distances. The difficulties, which ensue from the increasing volume of tasks at close distances seems more pronounced when such tasks are prolonged.

Everybody has roughly the same ocular physiological characteristics, common ancestry, two eyes and about 65 mm between them, so it would be reasonable to expect a large part of the population to be affected. In fact research in schools has shown that up to 60% of year 7 students show a predisposition to simple dyslexia, which is closely associated with the development of myopia. It does appear that these problems are the norm rather that the exception and that these sight-altering difficulties are normal for human beings in modern society.

The effect of prism When an object is viewed through a base out prism, for example in front of the right eye, its position is moved in, relative to the nose (see Fig 1 the effect of base out prism). The figure shows a right eye with a tendency to go down and in and the characteristic of a raised right eye-brow as the facial muscles and their associated extra-ocular muscles attempt to elevate the eye. If the extra-ocular muscles are already fighting a tendency (desire) for the right eye to move in, the prism will allow the eye to see the object from a more comfortable position. This is turn reduces the force of the extra-ocular muscles on the globe.

By appropriate use of prism (direction measured by the position of the thickest edge -base) at distance and near, the tension in the extra ocular muscles can be relaxed.

The increased tendency for an eye to turn in or out or up and down may be described as a latent squint (strabismus), or fixation disparity and is measured using a fixation disparity test (for example Brock String or Mallet) Fig 1 Base out prism in front of the right eye

R L

Eye displaced under the prism The effect of lens power Lens power is measured in Dioptres. If a positive lens of, say, 2 Dioptres is placed in front of an eye, which finds it difficult to focus on near things the tension in the cilliary muscle (intra-ocular muscle) will be relaxed. The Myolens uses a combination of prism in the appropriate directions of base at distance and near and dioptric power if necessary, to relax the myo-genic forces in the intra and extra-ocular muscles. It is designed to correct and prevent myopia.

Claims

<claim-text>CLAIMS1. An ophthalmic spectacle lens (not a bifocal lens with a visible or blended dividing line or a contact lens), in varifocal or single vision farm, which can incorporate prism usually designated by the four principle specified base directions-; IN, OUT, UP or DOWN -though it could be specified at any angle-and vary the amount, direction and rate at change of prism between the top and bottom of the lens.</claim-text> <claim-text>2. An ophthalmic varifocal or single vision lens as claimed in claim 1, which can treat incipient myopia due to a physiological deficit of vision 3. An ophthalmic varifocal or single vision lens as claimed in claim 1, which can prevent the onset of myopia.4. An ophthalmic varifocal or single vision lens as claimed in claim 1, which can be used to treat manifest myopia in order to prevent it increasing</claim-text>