Bifocal corneal contact lens
US RE25286 E
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Description (OCR text may contain errors)
Nov. 13, 1962 J. T. DE CARLE Re. 25,286
BIFOCAL coRNEAL CONTACT LENS Original Filed Nov. 18, 195'? INV EN TOR.'
United States Patent Orifice Re. 25,286 Reissued Nov. 13, 1962 l 25,286 BIFOCAL CORNEAL CONTACT LENS John Trevor de Carle, 9 St. Petersburgh Place, London, England Original No. 3,037,425, dated June 5, 1962, Ser. No. 697,277, Nov. 18, 1957. Application for reissue June 8, 1962, Ser. No. 205,153 Claims priority, application Great Britain Apr. 9, 1957 2 Claims. (Cl. 88-54.5)
Matter enclosed in heavy brackets appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.
This invention is concerned with contact lenses of an improved type.
It is well known that most people after `a certain age experience diiculty in seeing clearly both near and distant details. To overcome this it is common practice for one person to have two pairs of spectacles which correct the `vision for distance and for reading respectively. Alternatively, a single pair is often used in which each lens is formed of -two Zones of different focal lengths adjusted for each person to correct his vision both for distance and reading As far as I know there is no contact lens available commercially at the present time which is bifocal and, therefore able t-o correct by means of the same lens the vision for both distance and reading It is an object of this invention to provide such a contact lens.
According to the present invention the improved contact lens of the type described comprises a lens in which one zone is adapted to correct the distance vision of a patient and another zone -is adapted to correct his reading vision.
A preferred embodiment is illustrated in the accompartying diagrammatic drawings in which `FIGURE l shows a lens according to the invention and FIGURE 2 shows the lens in position on the eye. The lens comprises a small zone `1 Iat the centre which is designed to correct the distance vision and an outer zone 2 which corrects the reading vision. `It is applied to the cornea 3 of the eye 4, the lens of the eye being depicted at 5 with the iris at .6 and the pupil at 7. The area of t-he central zone 1 should in theory be equal to about half that of the pupil 7 under average lighting conditions but in practice a slightly larger distance zone than this is usually required because of lens movement on the eye. The greater the movement the larger the distance zone should be. The combined areas of the reading and distance zones `1 and 2 should be equal to or slightly larger than the largest size of the pupil 7.
In this embodiment the radius of curvature of the inner surface of the reading portion is made so that it lits the surface of the cornea in the usual way/while the radius of curvature of the inner surface of the distance portion is slightly smaller so that that portion stands slightly away from the eye.
The respective radii of curvature of the two zones of the lens are adjusted in accordance with the requirements of each particular patient and the material of which the lens is made. Allowance must also be made for the presence of the tear iiuid -between the lens and the eye, since this is of a dierent refractive index from the material of which the lens is constructed. When polymethyl methacrylate is used for making the lens it is found that the difference between the curvatures of the distance and reading portions and therefore the dioptral power must be about three and one-eighth times greater in air than that actually required in the eye.
The zones may be of various shapes and in various positions on the lens. For example they may be circular, oval or even semi-circular. They may be `formed in the lens by grinding and polishing each zone to its appropriate curvature or by moulding or by fusing together glasses or plast-ics of different refractive index. When it is desired to have a zone in the centre of different radius of curvature from that of the outer zone this is usually obtained by grinding the inside or concave surface of the lens. It is also possible to have a third zone of intermediate focal length between the distance and reading zones which will provide for correct vision at about one metrefrom the eye, that is, between the reading and distance positions. The different zones can be polished so las to give a gradual change from one to the other `without any sharp transition.
The invention may be applied to any known type of contact lens, providing that the optical system can be well centred and that the movement of the lens when tted to the eye is slight.
It is quite surprising that the wearer of lenses made according to the present invention is able to see correctly both near `and far det-ails without consciously having to look -in a different way for each, as he would with the known spectacle bifocal lenses. It appears that light reaches the retina all the time from both port-ions but when viewing ldistance the rays from the reading portion are so out of focus or ignored by the patient so that they do not interfere and vice versa.
1. A bifocal corneal contact lens of generally ccncavoconvex form having a maximum external dimension smaller than the limbus of the eye of the patient to Whom the lens is applied, said lens including a pair of concentric lens zones having a total area adapted to be only slightly greater than the largest normal area of the pupil of the eye, the central one of said lens zones being circular and having an area approximately half the area of the pupil under average lighting conditions so the patient can see simultaneously through both of said lens zones, the outer one of said lens zones having anterior and posterior curvatures to provide for the patients prescribed vision at close range, the central lens zone having yan anterior surface of the same curvature as said anterior surface of said outer lens zone, the posterior sur-face of said central lens zone being in the for-m of a spherical recess of shorter rad-ius of curvature than the radius of curvature of the posterior surface of said outer lens zone and defining, together with the tear iluid filling said recess, the distance prescription for the patient, the curvature of the posterior surface of said outer lens zone substantially conforming to the curvature of the cornea of t-he eye to provide a relatively tight tit for keeping the lens centered on the eye and for minimal movement so the patient can see simultaneously through .both of said lens zones for bifocal vision.
2. A bifocal corneal contact lens of generally concavoconvex for/n .having a maximum external dimension smaller than the limbus of the eye of the patient to whom the lens is applied, said lens including a 'central lens zone and an outer lens zone which together have a total area adopted to be only slightly greater than the larges! normal area of the pupil of the eye, said central lens zone being circular and having an area approximately half the area of the pupil under average lighting conditions so the patient can see simultaneously through both of said lens zones, the outer one of said lens zones having anterior and posterior curvatures to provide for the patient's` prescribed vision at close range, the central lens zone having an anterior surface of the same curvature as said lanterior surface of said outer lens zone, tlze posterior surface of said central lens zone being in the form of a spherical recess of shorter radius of curvature than the radius of curvature of the posterior surface of said outer lens zone and defining, together with the tear fluid lling said recess, the distance prescription for the patient, the curvature of the posterior surface of said outer lens zone :substantially conforming to the curvature of the cornea ofthe eye to provide a relatively tight fit for keeping the lens centered on the eye and for minimal movement so the patient can see simultaneously through both of said lens zones for bifocal vision.
References Cited in the le of this patent or the original patent UNITED STATES PATENTS 2,006,640 Hubbell July 2, 1935 2,129,305 lFeinbloox'n Sept. 6, 1938 2,198,868 AFeinbloom Apr. 30, 1940 2,274,142 Houchin Feb. 24, 1942 2,809,556 Hornstein .f Oct. 15, 1957 OTHER REFERENCES Sidelights on Refraction (Williamson-Noble), Ophthalmological Society of the United Kingdom, vol. LXXVI, pages 633-647, 1956.