Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – With antiglare or shading
Patent
1987-10-01
1990-02-06
Bovernick, Rodney B.
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
With antiglare or shading
G02C 716
Patent
active
048984590
DESCRIPTION:
BRIEF SUMMARY
This specification relates to spectacles and in particular to reading spectacles, i.e. spectacles for correcting presbyopia.
Presbyopia is frequently found in people from about age forty five onwards. It can occur as a natural part of the ageing process in people who have previously had good sight. It is usually possible to correct such presbyopia with lenses in the range of about +0.50 to +3.50 diopters. Generally, the right and left lenses are the same power because the two eyes in an individual age at the same rate.
Due to the nature of such presbyopia it is considered acceptable for people to choose ready made reading spectacles from a range, by testing them for comfort and clarity when reading. There are those who consider it necessary for an optician to be involved but a person should be reasonably capable of selecting spectacles with lenses of the correct power, without professional assistance. There are countries in the world where opticians do not have a monopoly and ready made reading glasses are freely available for customer assessment and selection.
However, whilst customers may be able to choose lenses of the correct power, it is not easy for them to ensure that the distance between the optical centres of spectacle lenses corresponds to the distance between the pupils. If the two distances differ substantially, then problems can occur. When a lens is positioned with its optical centre too far off the optical centre of the eye, the lens acts as a prism. This is undesirable and may lead to eyestrain, but a problem is that it may not be noticed at first. It is frequently only when a user has had the glasses for some time, that the problems begin.
There is thus a need for means by which a user can test whether the distance between the optical centres of lenses in spectacles corresponds to the inter pupil distance without expert assistance. Viewed from one broad aspect there is accordingly disclosed herein a spectacle lens provided with a removable mask with a relatively small window disposed around the optical centre of the lens.
In normal use two such lenses will be incorporated in spectacles and the invention extends to the provision of a pair of such spectacles. The masks are kept in place so that when a user tests the spectacles vision will only be possible through the two small windows. This will produce readily noticeable undesirable effects if the spectacles do not match the inter-pupil distance sufficiently closely. The user will not be able to see well or will see double images. Thus by testing the spectacles in this manner the user will be able more readily to determine whether this parameter is correct. Having selected spectacles which give the required clarity of vision through the mask windows, the user can then remove the masks for final checking, if desired, and subsequent use.
As will be appreciated from the discussion earlier, this proposal is likely to be of the greatest commercial significance in the case of reading spectacles, but it may also be of interest in other instances if it is considered feasible for users to choose ready made spectacles or if an optician wishes to use the system relying on a patient advising him as to what can be seen through the spectacles.
The size of the window in the mask should be determined in accordance with the power of the lens. The more powerful the lens, the smaller the window should be. The more powerful the lens, the smaller the amount of deviation which can be permitted. Tables are available which give the permitted deviation or tolerance for given lens powers. In general, the radius of a window centered on the lens optical centre will be of the same order as the maximum permitted deviation.
It may be found that it is possible to allow a greater prismatic effect vertically than horizontally, so that the testing window can be greater in the vertical direction. In that case the window could be in the form of an ellipse or oval with the major axis oriented in the direction which will be vertical in use. It may also be found that it is not ne
REFERENCES:
patent: 1452909 (1923-04-01), Covelle
patent: 1981439 (1934-11-01), Smith
Bovernick Rodney B.
Iris Optics Ltd.
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