WO2009079726A1

WO2009079726A1 - Intracomeal ring

Info

Publication number: WO2009079726A1
Application number: PCT/BR2007/000359
Authority: WO
Inventors: Paulo Ferrara De Almeida Cunha
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-12-26
Filing date: 2007-12-26
Publication date: 2009-07-02
Anticipated expiration: 2010-06-26

Abstract

An intracomeal ring (1) comprising a 90° to 360° arc of cornea bio compatible inert transparent material having a triangular cross section, conta ins colour pigmentation so as to filter light radiation and thus limit the quantity and quality of the light that reaches the retina. Preferably the colour of the pigmentation is yellow.

Description

Title: ¹¹I NTRACO RN EAL RING"

The present invention refers to intracorneal rings used in the correction of myopia and other forms of ametropy. Background of the Invention The use of intracorneal rings was originally proposed by a

Russian doctor, Blavaskaya, who, in 1966, used rings made of corneal tissue for correcting high degrees of ametropy. In 1986 Fleming proposed using, hexagonal section, large diameter rings of variable thickness for correcting low degrees of myopia. Almost at the same time, Paulo Ferrara (see Brazilian Patent Pl 8705060) proposed the use of triangular section, small diameter rings of variable thickness for correcting moderate and elevated degrees of myopia.

The so-called lntacs and Ferrara rings, which are the two basic types of intracorneal rings used today, use transparent materials that are biocompatible with respect to the human cornea. The transparency of the material, however, causes a high degree of refraction which, in its turn and when the light reaches the retina, cause considerable discomfort to the user who is dazzled, especially at night. Object of the invention The object of the present invention is to ameliorate the problems that result from refraction for users of Ferrara intracorneal rings which, in their presently preferred form, comprise a 90° to 360° arc of cornea biocompatible inert transparent material (for example, PMMA - polymethylmethacrylate), the ring having a scalene triangular cross section of which the base is the longest side and the shortest side is the outer side, the plane defined by the lower outer edge of the ring being lower than the plane defined by its lower inner edge, whereby the base of the ring, corresponding to the longest side of the triangle, defines a truncated cone.

Since the rings mentioned herein are in reality arcs of up to 360°, the term ring is to be understood to include such partially annular segments. Summary of the Present Invention

According to the present invention an intracorneal ring comprising a 90° to 360° arc of cornea biocompatible inert transparent material having a triangular cross section is characterised by containing colour pigmentation so as to filter light radiation and thus limit the quantity and quality of the light that reaches the retina. Preferably the pigmented transparent material is yellow PMMA having high light transmittance properties (for example, 90%) which, in a referred embodiment filters light such as to present an ultraviolet absorption at 410 nm of about 0.12/mm. The preferred yellow PMMA material has a refraction index of approximately 1.492. In the preferred embodiments of the invention, the triangular cross section is in the form of a scalene triangle of which the base is the longest side and the shortest side is the outer side, the plane defined by the lower outer edge of the ring being lower than the plane defined by its lower inner edge, whereby the base of the ring, corresponding to the longest side of the triangle, defines a truncated cone.

The outer diameter of the ring may suitably vary from 5 mm to 6 mm and the thickness of the ring may be in the range of 0.15 mm to 0.40 mm. The height of the ring from the base of the triangle to its apex is preferably also from 0.15 mm to 0.40 mm. It has been found that, notwithstanding the yellow pigmentation throughout the material of the ring, once the ring is implanted in the cornea, the yellow colour is not discernable to the observer and the visual appearance is the same as when the ring is made of clear non-pigmented material. Brief Description of the Drawings

The invention will be better understood from the following description of preferred embodiments, given by way of example, reference being made to the accompanying drawing which shows a 180° ring and its possible cross sections. Detailed Description of the Invention

Referring now to the drawing, an intracomeal ring 1 is in the form of an arc of approximately 120°. The ring is made of PMMA (poly- methylmethacrylate) which is inert and biocompatible with respect to the cornea, although other suitable materials with similar properties could be sued.

The width of the ring shown in the drawing is 0.6 mm and has internal and external diameters of 4.40 mm and 5.60 mm, respectively. At each end of the ring there is a small orifice 2 having a diameter of 0.20 mm that is used for manipulating the ring during the implant operation.

Ring 1 has a scalene triangular cross section, that is to say, the three sides of the triangle are of different lengths. The drawing shows two details of suitable cross sections, by way of example. In one case, shown on the lower left hand side of the drawing, the base 3 is the longer side and is 0.60 mm long whereas the height measured between the base 3 and the apex 4 of the triangle is 0.15 mm. In the other case that is illustrated, the base 3' is also 0.60 mm whereas the height is 0.35 mm, although it could vary to about 0.40 mm. In both cases however, the base of the ring defines a truncated cone the angle of which can vary up to 45°, the angle being chosen to be tangential to the cornea in accordance with its curvature at the position where the ring is being implanted.

It is to be observed that the shortest side 5 or 5' of the scalene triangular section corresponds to the outer face of the ring whereas the side of intermediate length 6 or 6' corresponds to the inner face.

The curvature of the base of the ring (that is to say, the angle of the truncated cone defined by base 3, 3' which is designed to be tangential to the cornea at the point of implantation) is always chosen in accordance with the necessities of the patient. This will determine the external diameter of the ring which usually varies between about 5 mm and 6 mm. The ring examplified in the drawing has an external diameter of 5.60 mm and an internal diameter of 4.40 mm.

Although the intracomeal ring illustrated in the drawing and as described above has met with great success, it has, as mentioned above, the drawback of dazzling the patient due to refraction, especially at night. In accordance with this invention, a yellow pigment is incorporated in the ring material (PMMA) so that the ring 1 effectively comprises a yellow filter. The result is that the quality and quantity of light that reaches the retina is modified and this improves the quality of the optical system of the eye.

Moreover, once the ring has been implanted in the cornea the yellow colour of the ring is not visible to others and thus the beneficial effects of the filter do not affect the appearance of the user.

The ring material used in the preferred embodiment is a yellow pigmented PMMA pigment used may conveniently have the following specification: Index of refraction: 1.492 ± 0,002

Specific gravity: 1.190 ± 0.005

Luminous transmittance: 90%

UV absorption at 410 nm = 0.12/mm

It has been found that in the case of the preferred embodiment and notwithstanding the yellow pigmentation throughout the material of the ring, once the ring is implanted in the cornea, the yellow colour is not discernable to the observer and the visual appearance is the same as when the ring is made of clear non-pigmented material.

Other pigmented inert materials may also be used which are not necessarily yellow in colour provided that they have a suitable filtering effect combined with high transmittance.

Claims

1. lntracorneal ring comprising a 90° to 360° arc of cornea biocompatible inert transparent material having a triangular cross section, characterised by containing colour pigmentation so as to filter light radiation and thus limit the quantity and quality of the light that reaches the retina.

2. lntracorneal ring according to claim 1 , characterised in that said pigmentation is yellow.

3. lntracorneal ring according to claim 1 or 2, characterised in that said pigmented material has a luminous transmittance of about 90% and a U V absorption at 410 nm of about 0.12/mm.

4. lntracorneal ring according to any one of the previous claims, characterised in that said trianguloar cross section is in the form of a scalene triangle of which the base is the longest side and the shortest side is the outer side, the plane defined by the lower outer edge of the ring being lower than the plane defined by its lower inner edge, whereby the base of the ring, corresponding to the longest side of the triangle, defines a truncated cone.

5. lntracorneal ring according to claim 4, characterised in that the outer diameter of the ring is- between 5 mm and 6 mm and the thickness of the ring is in the range of 0.15 mm to 0.40 mm.

6. lntracorneal ring according to claim 4 or 5, characterised in that the height of the ring from the base of the triangle to its apex is from 0.15 mm to 0.40 mm