Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Eye prosthesis – Intraocular lens
Patent
1997-12-29
1999-10-19
Yu, Mickey
Prosthesis (i.e., artificial body members), parts thereof, or ai
Eye prosthesis
Intraocular lens
128898, A61F 216
Patent
active
059680954
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a method of preoperatively selecting an intraocular lens to be implanted into an eye to postoperatively render the eye emmetropic or ametropic with any desired postoperative refraction.
BACKGROUND OF THE INVENTION
To obtain a desired postoperative refractive outcome of an intraocular lens implantation--emmetropia or ametropia--, there are several methods in use to determine which dioptric power the intraocular lens to be implanted, should have. The correct implant power to choose depends on the axial distance from the cornea, at which the intraocular lens (IOL) will end up in the eye.
With the present techniques, the axial position of the IOL can only be estimated.
Two major schools exist today for estimating the axial position of the IOL.
One school describes the optics of the eye in terms of thin lens theory.
In this connection reference is hereby made to: lens. Vestn. Oftamol 1967;80(4):27-31, distant vision. Br J Ophthalmol 1973;57:735-740, Am Intra-Ocular Implant Soc J 1975;1(1):4-5, prepupillary lens in the aphakic eye. Bibliotheca Ophthalmol 1975;83:273-275, calculation of the refractive power and its accuracy. Ophthalmologica 1975;171:467-486, Ophthalmic Surg 1975;6(3):17-31, and refining intraocular lens power calculations. J Cataract Refract Surg 1988;14:17-24.
The axial position of the IOL is mostly considered to be a constant, often referred to as the ACD constant. The value of the constant depends to some extent on the IOL model. In the thin lens theory, this constant represents the postoperative distance between the principal planes of the cornea and of the IOL.
Another school applies retrospective statistical analysis of clinical data to determine a coefficient, the so called A-constant, in a linear equation, known as the SRK formula, linking corneal dioptric power K, eye length L, IOL power and postoperative refraction.
In this connection reference is made to: the Binkhorst, Colenbrander, and SRK.TM. implant power prediction formulas. Am Intra-Ocular Implant Soc J 1981; 7:337-340, and other second generation formulas. J. Cataract Refract Surg 1988;14:136-141, and of the SRK/T formula and other theoretical and regression formulas. J Cataract Refract Surg 1990; 16:341-346.
The linear relationship mentioned above, is not a theoretically correct representation of the optics of the eye, but the SRK approach is most widely used because it is simple and, in clinical practice, yields results similar to the thin lens theory approach.
The SRK/T formula in the above reference 10), is a hybrid between the two approaches.
In both schools, further refinement entails corrections depending on mainly eye length.
The following references: Gaussian optics. J Cataract Refract Surg 1987; 13:141-145, Linsen-Systems Brille-Kontaktlinse-Hornhaut-Augenlinse (IOL), in: Schott K, Jacobi K W, Freyler H (Hrsg): 4 Kongr. d. Deutsch. Ges. f. Intraokularlinsen Implant., Essen 1990. Berlin, Heidelberg, New York, Springer Verlag 1990, and Cataract Refract Surg 1991; 17:194-198, problem of pre-estimating the axial position of the IOL remains.
The position of the IOL optic is determined by its fixation in the eye. Fixation is mostly obtained by means of attachments to the optic, so called loops, that hold the lens in place by spring action against ocular tissue. The most common site of placement of the IOL today is inside the capsular bag. Alternative placements are in the ciliary sulcus and in the anterior chamber angle. Lenses that are fixed to the iris also exist, but fixation is then not by spring action. There are also lenses meant for capsular bag placement that do not possess loops or exert spring action, such as disc lenses, plate lenses, and capsular bag filling lenses.
SUMMARY OF THE INVENTION
The object of the invention is to bring about a method of preoperatively selecting an intraocular lens to be implanted into an eye to postoperatively render the eye emmetropic or with any other chosen refractive outcome, which method should be applicable to all types of IOLs.
Thi
REFERENCES:
patent: 4710193 (1987-12-01), Volk
patent: 5282852 (1994-02-01), Capetan et al.
Norrby, Eur. J. Implant. Ref. Surg, 7, pp. 202-209 ( Aug. 1995).
Norrby et al, J. Cataract Refract. Surg, 23, pp. 254-259(Mar. 1997) .
O'Hara Kelly
Pharmacia & Upjohn Groningen BV
Yu Mickey
LandOfFree
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