GB2489501A

GB2489501A - Contact lens with diffractive or Fresnel prism

Info

Publication number: GB2489501A
Application number: GB1105475.6A
Authority: GB
Inventors: Geraint William Griffiths
Original assignee: SVUK Ltd
Current assignee: SVUK Ltd
Priority date: 2011-03-31
Filing date: 2011-03-31
Publication date: 2012-10-03
Also published as: GB201105475D0

Abstract

An ophthalmic varifocal or single vision contact lens which can incorporate diffractive or Fresnel prism in the four principle base specified directions; IN, OUT, UP and DOWN and/or vary the amount, direction and rate of change of prism between the top and bottom sectors of the lens. The lens acts to relive the symptoms that can be associated with binocular imbalance and to correct and prevent myopia.

Description

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

Description

The Contact Myolens in appearance to a casual observer, will look like an ordinary contact lens. The more experienced observer will see that the lens has prism ballast or other stabilizing mechanism to maintain a fixed orientation on the eye. It may also have a series of feint parallel vertical or horizontal lines running across the central or whole part of the lens (see Figi the contact Myolens) The most informed observer will be able to tell by observation or using instruments that the purpose of the lines is to induce a horizontal or vertical prismatic effect in one or both lenses. This prismatic defect may increase or decrease in the lower part of the lens depending on what future technology can produce. These lenses could be single vision or varifocal, sphere or toric. The prismatic effect in the Contact Myolens could be induced by a Fresnel or defractive prism effect or some other means across the whole of the lens, which allows it to be stabalised by conventional means (prism ballast or dynamic lid control) in the horizontal position The Myolens may require free form, computer generated laser technology or advanced molding techniques.

Although vertical prism (base down prism) is part of the production of normal toric contact lenses, horizontal or base up prism is much more problematic because conventional manufacturing techniques mean that the lens is thicker and heavier at one edge of the lens that the other. This means that a prism with it thick nasal edge (base in prism) will immediately gravitate into the vertical position. Similarly a base up prism will quickly turn through 90 degrees and become base down By using a refractive or Fresnel technique the prismatic effect is distributed evenly over the whole surface of the lens and therefore only needs a conventional prism ballast lens to stabalise it in the required position The prismatic effect could be base in or out or neutral in the distance parts of the lenses and similarly at near base in or out or neutral, but varying independently from the distance.

Background

The purpose of this contact lens 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 mechanical forces generated in the intra (cilliary muscle) and extra-ocular muscles to maintain a clear focus and binocular vision, can distort a growing eye (especially if already compromised by nutritional deficit and a softened globe {sclera}). This can lead to axial and refractive focusing problems (short sight, astigmatism and anisometropia {different powered eyes}) The intention of the Contact Myolens is to reduce these spurious effects and relive the symptoms that can be associated with binocular imbalance. There is also a possibility, that when signs of ocular stress are seen (incipient myopia) use of the Myolens will reverse the tendency to myopia, that is prevent if happening. The need for the prism and the direction in which it is prescribed is measured by a fixation-disparity test at distance and near. The effect of the correction is 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 21 sI century because of the explosion in very recent times of computer use and extended periods of close work with which human beings are not evolved to deal. The need to coordinate the eyes in the distance is essential for survival but it is only quite recently that survival (or at least a reasonable standard of living) is beginning to be dependant on the same binocular skill at the near point. The difficulties come from the need to converge the eyes to objects very close, for extended periods of time using a prehistoric visual system, which was designed mainly for looking in the distance.

Everybody has roughly the same 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 school research has shown that up to 60% of year 7 students show a predisposition to simple dyslexia, with which the development of myopia is closely. It does appear that these sight-altering difficulties could be the norm for a small majority in modern society.

The effect of prism When an object is viewed through a base out prism in front of the right eye, its position is moved in, relative to the nose (see Fig 2 the effect of base out prism). The fig 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 (eye ball). By appropriate use of prism 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 may be described as a latent squint (strabismus), or fixation disparity and is measured using a fixation disparity test (Brock String or Mallet) 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 Contact Myolens uses a combination of prism in 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

CLAIMS1. An ophthalmic varifocal or single vision contact lens which can incorporate defractive or Fresnel prism in the four principle base specified directions; IN, OUT, UP and DOWN and or vary the amount, direction and rate of change of prism between the top and bottom sectors of the lens.
2. An ophthalmic varifocal or single vision contact lens as claimed in claim 1, which can relieve symptoms of incipient myopia due to physiological deficits of vision
3. An ophthalmic varifocal or single vision contact lens as claimed in claim 1, which can prevent the onset of physiological myopia.
4. An ophthalmic varifocal or single vision contact lens as claimed in claim 1, which can be used to correct manifest myopia to prevent it increasing