GB2031178A

GB2031178A - Contact lens

Info

Publication number: GB2031178A
Application number: GB7839428A
Authority: GB
Original assignee: KWOK-CHU FUNG J
Current assignee: KWOK-CHU FUNG J
Priority date: 1978-10-05
Filing date: 1978-10-05
Publication date: 1980-04-16
Also published as: DE2940352A1; JPS5550216A; JPS5621134B2; HK16483A

Abstract

A contact lens comprises an optical zone and a peripheral zone, the latter having two opposite areas cut away to form a sink segment 8 and a secondary segment 11, the sink segment 8 being heavier than the secondary segment 11 and being defined by a line, such as an arc or chord. The lens may be of soft hydrophilic material. The design inhibits rotation and axis displacement during use. <IMAGE>

Description

SPECIFICATION Contact lenses Technical field The present invention relates to soft contact lenses.

Background art An outstanding difficulty encountered in wearlng a cylindrical soft contact lens is that it cannot be maintained in its proper axis position on the cornea of the eyeball, owing to the normal blinking action of the wearer or patient. Every blinking action of the eye will cause a rotation of the contact lens, either clockwise or anti-clockwise. Thus, the prescribed axis position of the lens cannot be maintained so as to obtain the best vision. This renders it pointless to incorporate a cylindrical correction, for patients with astigmatism, to such soft contact lenses.

One attempt to overcome the problem of rotation of the contact lens during use has been to employ a truncated prism base down ballast design. However, this has two disadvantages: Firstly, the design renders itdifficultto position properly the optical centre of the lens with the visual axis of the eye.

Secondly, the bottom ofthe lens, which is compa rativelythick, creates an uncomfortable feeling on the lower eyelid of the patient.

Disclosure ofthe invention The present invention now provides a soft contact lens comprising a central optical zone and a peripheral zone, characterised in that the peripheral zone comprises (a) a sink segment formed by a depression in the anterior face thereof, said sink segment being defined by a line joining two points on the circumference of the peripheral zone, and (b) a secondary segment diametrically opposite the sink segment, the secondary segment having a lower mass than the sink segment.

Preferably, the sink segment will be defined by a chord or arc and will be formed as a depression of even depth relative to the anterior face of the peripheral zone. It is preferred that the secondary segment be defined by an arc.

As the secondary segment has a lower mass or weight than the sink segment, the lens, after it has been fitted to the eyeball, will self-align with the sink segment in the lowermost position; the line defining the sink segment will assume a generally horizontal position, just above the lower eyelid.

It will be seen that the contact lens of the present invention has several advantages over the prior-art lenses. Thus, blinking actions will not affect the position of the lens, owing to the heavier weight of the sink segment portion relative to the secondary segment portion. Thus, the design of the present lens (which may be generally characterised as a "peripheral visible axis cylindrical soft contact lens") helps two maintain the axis of the lens and to inhibit rotation of the lens. Moreover, in the case of unilateral cylindrical prescriptions, prismatic jump of the image is inhibited.

The lens of the present invention can incorporate a prismatic power correction for the treatment of heterophoria to a certain extent.

Moreover, the present design permits precise control of fitting. The visible line, in general a chord or arc, defining the sink segment portion serves as a reference line t6 the cylindrical axis, thereby giving the practitioner proof of the stability of the lens position during the fitting process and during the wearing period. The secondary segment may also function as a guide to the practitioner.

Also, the sink segment can interact with the lower eyelid and thereby aid- in maintaining the position of the lens on the eyeball.

The process of producing the sink segment and the secondary segment can be easily incorporated into the conventional production procedures for soft contact lenses.

Thus, the present invention also provides a method of manufacturing a contact lens according to the present invention, which comprises the steps of producing a contact lens having an optical zone and a pheripheral zone; incorporating spherical andior cylindrical corrections in the optical zone in accord ance with the prescription for the intended wearer; establishing a line joining two points ofthe circumference of the peripheral zone to define the sink segment and mechanically cutting, e.g. by means of eccentricity, said sink segment in the anterior face of the peripheral zone; mechanically cutting a secon dary segment diametrically opposite the sink seg ment, usually by means of eccentricity, so that the secondary segment has a lower mass than the sink segment; and, optionally, forming a front edge bevel to the lens.

Cutting by eccentricity involves placing the lens in an eccentric position to the axis of the tool carrier from which the form is being established.

Brief description of drawings Figure 1A is a view of the anterior face of a soft contact lens representing a minus lens forthe correction of short-sightedness.

Figure 1B is a vertical section along the line B-B of Figure 1A.

Figure 2A is a view of the anterior face ofthe contact lens of Figure 1A, having a sink segnient, defined by an arc, formed therein.

Figure 2B is a vertical section through the line B-B in Figure 2A.

Figure 3A is a view of the anterior face ofthe lens of Figure 2A, having a secondary segment and front edge bevel formed therein.

Figure 3B is a vertical section along the line B-B in Figure 3A.

Figure 4A is a view of the anterior face of the contact lens of Figure 1A, having a sinksegment, defined by a chord formed therein.

Figure 4B is a vertical section along the line B-B in Figure 4A.

Figure 5A is a view of the anterior face of the contact lens of Figure 4A having a secondary segment and front edge bevel fornied therein.

Figure 5B is a vertical section along the line B-B in 'Figure 5A.

Figure 6A is a view of the anterior face of a contact lens representing a plus lens for the correction of far-sightedness.

Figure 6B is a vertical section along the line B-B of Figure 6A.

Figure 7A is a view of the anterior face of the contact lens of Figure 6A, having a sink segment, defined by an arc, formed therein.

Figure 78 is a vertical section through the line B-B in Figure 7A.

Figure 8A is a view of the anterior face of the lens of Figure 7A, having a secondary segment and front edge bevel formed therein.

Figure 8B is a vertical section along the line B-B in Figure 8A.

Figure 9A is a view of the anterior face of the contact lens of Figure 6A, having a sink segment, defined by a chord, formed therein.

Figure 9B is a vertical section along the line B-B in Figure 9A.

Figure lOA is a view of the anterior face of the contact lens of Figure 9A having a secondary segment and front edge bevel formed therein.

Figure 10B is a vertical section along the line B-B in Figure 10A.

Description ofpreferred embodiments The lens shown in Figure 1A may be fabricated from a hydrophilic material, as is customary for soft contact lenses. The lens will normally having a diameter of at least 1 2.0mm. As shown, the lens comprises two zones, an optical zone having a circular perimeter 2 and a peripheral zone 3 defined by the perimeter 2 and the outside circumference 4 of the lens. The optical zone 1 is approximately 8 mm in diameter and the peripheral zone 3 preferably has a width (i.e. the radial distance between the opticalzone perimeter 2 and the circumference 4) of 2 mm to 3.5 mm.

Preferably, the outside (anterior) face of the peripheral zone 3 (also known as the "lens carrier") has a concavity of minus 4.00 dioptre to minus 6.00 dioptre relative to the base curvature of the inside or posterior face 6 of the lens. Accordingly, the peripheral zone is thicker at the outside edge or circumference 4 than at the optical-zone perimeter 2.

As shown in Figures 2A and 2B, a depression is mechanically cut into the anterior face 5 of the peripheral zone, establishing a visible arc 7 and leaving a sink segment 8 the boundaries of which are the arc 7 and the circumference 4; as can be seen from Figure 2A, the arc 7 touches the optical-zone perimeter or margin 2 substantially tangentially at a point 9.

The next stage of the manufacturing process is indicated in Figures 3A and 3B. An area of the face 5 of the peripheral zone directly opposite the sink segment 8 is mechanically cut away by eccentricity, establishing a secondary arc 10 which defines, with the circumference 4, a secondary segment 11 of reduced weight and thickness; in particular, the mass of the secondary segment 11 is less than the mass of the sink segment.

Finally, a front edge bevel may be formed near the circumference 4 of the anterior face 5 of the peripheral zone 3. The bevel 12 reduces the edge thickness of the lens, thereby increasing the comfort whilst it is being worn.

As can be seen in Figure 3A, the areas of the sink segment and secondary segment are congruent.

It should be noted here that, in order to avoid unnecessary repetition in the discussion of the remaining drawings, like parts are indicated by like numerals.

The lens shown in Figures 5A and 5B is similar to that shown in Figures 3A and 3B except that the sink segment 8 is defined not by an arc but by a visible chord 13. In this lens, the sink segment 8 and the secondary segment 11 are not congruent, since the latter is defined still by a secondary arc.

The secondary segment is, in general, formed by a secondary arc (rather than a secondary chord) because (a) it is easier to manufacture mechanically and technically and (b) it reduces the friction of the upper eyelid with the margin of the lens (the segment margin). A straight-line margin would cause the edges of 1 he perimeter, where the segment is cut, to be pc inted and therefore would cause greater irritation. The lower eyelid is stable and therefore a chord would not cause the same sort of irritation.

Figures 4A and 4B represent a stage in the manufacture of the lens of Figure 5A and Figure 5B, wherein only the sink segment 8 has been formed.

The contact lens shown in Figures 6A and 6B is similartothatshoun in Figures 1Aand 1B,except that the optical zone 1 has a different correction.

Figures 8A and 8E3 illustrate a finished contact lens developed from the lens of Figures 6A and 6B, and incorporating featu -es analogous to those shown in Figures 3A and 3B. igures 7A and 7B illustrate an intermediate stage n the production of the lens of Figures 8A and 8B.

The finished lens shown in Figures 10Aand 10B is an alternative development from the lens of Figures 6A and 6B and incorporates features analogous to those shown in Figures 5A and 5B. Figures 9A and 9B represent an intermediate stage in the manufacture of the lens of Figures 1 OA and lOB.

Of course, variations from the illustrated embodiments are possible. For example, the chord or arc defining the sink segment need not meet the perimeter or the margin of the optical zone at a tangent.

It may vary from prescription to prescription.

Similarly, although the sink segment and the secondary segment are congruent in the lens of Figure 3A and the lens of Figure 8A, this need not always be the case; again it may vary from prescription to prescription.

The soft lens of this invention may be made of any, appropriate material. For example, as an alternative to a hydrophilic material, a suitable silicone rubber could be used; in this case, however, a moulding technique might be used in the lens manufacture.

In the case of a lens with a mild prescription, it may be necessary to provide additional prismatic ballast to stabilise the position of the lens, as thinner lenses would require greater mass.

Claims

1. A soft contact lens comprising a central optical zone and a peripheral zone, charactarised in that the peripheral zone comprises (a) a sink segment formed by a depression in the anterior face thereof, said sink segment being defined by a line joining two points on the circumference of the peripheral zone, and (b) a secondary segment diametrically opposite the sink segment, the secondary segment having a lower mass than the sink segment.

2. A contact lens according to claim 1, characte rised in that the sink segment is formed as a depression of even depth relative to the anterior face ofthe peripheral zone.

3. A contact lens according to claim 1 or 2, characterised in that the line defining the sink segment is a chord or arc.

4. A contact lens according to claim 1,2 or 3 characterised in that the secondary segment is defined by an arc.

5. A contact lens according to any of claims 1 to 4, characterised in that the peripheral zone is provided with a front-edge bevel.

6. A contact lens according to any of claims 1 to 5, characterised in that the anterior face of the peripheral zone has a basic concavity of -4.00 dioptre to -6.00 dioptre relative to the posterior face of the lens.

7. A contact lens according to any of claims 1 to 6, characterised in that it is made of hydrophilic material.

8. A contact lens according to any of claims 1 to 7, characterised buy a minimum diameter of 12 mm and a width of the peripheral zone of 2 mm to 3.5 mm.

9. A contact lens substantially as herein described and as illustrated in Figures 3A and 3B, in Figures 5A and 5B, in Figures 8A and 8B, or in Figures 10A and 10B.

10. A method of manufacturing a contact lens according to any of claims 1 to 9 which comprises the steps of providing a contact lens having an optical zone and a peripheral zone; incorporating spherical and/or cylindrical corrections in the optical zone, establishing a line joining two points of the circumference of the peripheral zone to define the sink segment in the anterior face of the peripheral zone; mechanically cutting said sink segment in the anterior face of the peripheral zone; mechanically cutting a secondary segment diametrically opposite the sink segment so that the secondary segment has a lower mass than the sink segment; and, optionally, forming a front edge bevel.

11. A method according to claim 10, characte rised in that the sink segment and/or the secondary segment is/are formed by eccentricity.