RU2523150C1 - Method for measuring intraocular lens power with intracapsular fixation following previous excimer laser keratectomy - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: eye length (L), curve radius of the anterior surface of the cornea (R), intraocular lens constant A (A), curve radius of the posterior lens of the cornea (R_P), corneal diameter (d) and corneal thickness in the centre (H) are measured. The intraocular lens power (Diol) is measured by formula: $$D_{iol}=\frac{1336\left(1336-L\frac{333}{R}\right)}{\left(L-p\right)\left(1336-p\frac{333}{R}\right)},$$

wherein p is a distance of the anterior surface of the intraocular lens and an apex of the cornea following an excimer laser keratectomy, mm. The p value is determined as: $$p=R_P-\sqrt{R_P^2-\frac{{\left(d-\mathrm{1,82}\right)}^2}{4}}+\mathrm{0,62467}A+H-\mathrm{70,983.}$$

EFFECT: method enables providing more accurate measurement of the intraocular lens power with intracapsular fixation following the previous excimer laser keratectomy ensured by taking into account the curve radius of the anterior surface of the cornea, the diameter of the cornea and the intraocular lens constant A.

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Description

The invention relates to the field of ophthalmic surgery.

A known method for determining the optical power of an intraocular lens (IOL) with intracapsular fixation for the correction of ametropia according to the patent of the Russian Federation No. 2201724. The method includes measuring the length of the eye, the radius of curvature of the anterior surface of the cornea, the refraction of the cornea, the distance between the anterior surface of the IOL and the apex of the cornea, the depth of the anterior chamber, the thickness of the natural lens, the diameter of the optical and haptic parts of the IOL and the angle of inclination of the haptic part to the plane of the optical part.

However, this method has a significant drawback: it has insufficient accuracy in calculating the IOL for the eyes of patients after a previous excimer laser keratectomy operation. This leads to a decrease in visual function in such patients, the correction of which requires additional surgical interventions.

EFFECT: increased accuracy of determining the optical power of an intraocular lens with intracapsular fixation after previously performed excimer laser keratectomy.

The technical result is achieved by the fact that in the method for determining the optical power of an intraocular lens with intracapsular fixation after a previously performed excimer laser keratectomy, including measuring the length of the eye, the radius of curvature of the anterior surface of the cornea, the refraction of the cornea and the constant A of the intraocular lens, additionally measure the radius of curvature of the posterior surface of the cornea and cornea in the center, and the optical power of the intraocular lens is determined by the formula:

$$D_{\mathrm{and}\mathrm{about}l}=\frac{1336\left(1336-L\frac{333}{R}\right)}{\left(L-p\right)\left(1336-p\frac{333}{R}\right)}$$

where D _iol is the optical power of the intraocular lens, diopter;

L is the length of the eye, mm;

333 / R - standardized refraction of the cornea, diopters;

R is the radius of curvature of the anterior surface of the cornea, mm;

p is the distance between the front surface of the intraocular lens and the apex of the cornea after excimer laser keratectomy, mm, determined by the formula:

$$p=R_s-\sqrt{R_s^2-\frac{{\left(d-1.82\right)}^2}{\mathrm{four}}}+0.62467A+H-\mathrm{70,983}$$

R _s - the radius of curvature of the posterior surface of the cornea, mm;

A is the constant A of the intraocular lens;

H is the thickness of the cornea in the center, mm;

d is the diameter of the cornea, mm.

These proportions are selected empirically.

When determining the distance between the anterior surface of the intraocular lens and the apex of the cornea according to the invention, the radius of curvature of the posterior surface of the cornea, the diameter of the cornea and the value of the factory constant A of the intraocular lens are taken into account.

After an excimer laser keratectomy operation, the cornea after ablation, that is, after removal of tissue from the anterior surface, has a smaller corneal thickness and a greater radius of curvature of the anterior surface. Moreover, using excimer laser keratectomy technology, the radius of the posterior surface of the cornea is practically unchanged and can serve as a reference surface for the predicted position of the IOL, the optical power of which must be determined. Therefore, the determination of the distance between the front surface of the intraocular lens and the apex of the cornea according to the prototype formula, based on the radius of curvature of the front surface of the cornea, gives overestimated values, leading to a significant error in determining the optical power of the IOL.

The set of essential distinguishing features proposed by the authors is necessary and sufficient for the unambiguous achievement of the claimed technical result.

The method is as follows.

On the patient’s eye with a previously performed excimer laser keratectomy, the length of the eye, the radius of curvature of the anterior surface of the cornea, the refraction of the cornea and the constant A of the intraocular lens, the radius of curvature of the posterior surface of the cornea and the thickness of the cornea are measured. The optical power of the intraocular lens is determined by the formula:

$$D_{\mathrm{and}\mathrm{about}l}=\frac{1336\left(1336-L\frac{333}{R}\right)}{\left(L-p\right)\left(1336-p\frac{333}{R}\right)}$$

where D _iol is the optical power of the intraocular lens, diopter;

L is the length of the eye, mm;

333 / R - standardized refraction of the cornea, diopters;

R is the radius of curvature of the anterior surface of the cornea, mm;

p is the distance between the front surface of the intraocular lens and the apex of the cornea after excimer laser keratectomy, mm, determined by the formula:

$$p=R_s-\sqrt{R_s^2-\frac{{\left(d-1.82\right)}^2}{\mathrm{four}}}+0.62467A+H-\mathrm{70,983}$$

R _s - the radius of curvature of the posterior surface of the cornea, mm;

A is the constant A of the intraocular lens;

H is the thickness of the cornea in the center, mm;

d is the diameter of the cornea, mm.

The method is illustrated by the following examples.

Example 1. Patient A., 52 years old. Diagnosis: Right eye - cataract after excimer laser keratectomy 18 years ago. According to the invention, the radius of curvature of the front surface of the cornea was measured: 8.4 mm, eye length: 25.2 mm, corneal diameter: 11.5 mm; radius of curvature of the posterior surface of the cornea: 7.5 mm. An artificial lens model with a constant A equal to 118.6 was chosen for implantation.

Ophthalmoscan Model-200 from Sonometrics Systems Inc. was used to measure eye length. (USA), radius of curvature of the anterior surface of the cornea - TOPCON autokeratometer (Japan), radius of curvature of the posterior surface of the cornea on a Pentacam HR Oculus device (Germany), technological parameters of the IOL are indicated by the lens manufacturer in the product passport.

Substituting the measured values in the formula, according to the invention received: D _iol = 18,45dptr.

An artificial lens with an optical power of 18.5 diopters was implanted.

1 month after surgery: visual acuity without correction of 1.0.

Example 2. Patient G., 49 years old. Diagnosis: Left eye - cataract after excimer laser keratectomy 25 years ago. According to the invention, the radius of curvature of the anterior surface of the cornea was measured: 8.9 mm, eye length: 25.85 mm, corneal diameter: 11.2 mm; radius of curvature of the posterior surface of the cornea: 8.0 mm For implantation, an artificial lens model with a constant A of 118.6 was chosen.

Ophthalmoscan Model-200 from Sonometrics Systems Inc. was used to measure eye length. (USA), radius of curvature of the anterior surface of the cornea - TOPCON autokeratometer (Japan), radius of curvature of the posterior surface of the cornea on a Pentacam HR Oculus device (Germany), technological parameters of the IOL are indicated by the lens manufacturer in the product passport.

Substituting the measured values in the formula, according to the invention received: D _iol = 19.04 diopters.

An artificial lens with an optical power of 19.0 diopters was implanted.

1 month after surgery: visual acuity without correction of 1.0.

Thus, thanks to the proposed method for determining the optical power of an intraocular lens with intracapsular fixation after an excimer laser keratectomy has been performed to correct aphakia after cataract extraction, the calculation accuracy is increased by at least 20% and the refractive error is minimized.

Using the proposed method will provide high accuracy in determining the optical power of an intraocular lens with intracapsular fixation after previously performed excimer laser keratectomy.

Claims (1)

A method for determining the optical power of an intraocular lens with intracapsular fixation after previously performed excimer laser keratectomy, including measuring the length of the eye, the radius of curvature of the anterior surface of the cornea, the refraction of the cornea and the constant A of the intraocular lens, characterized in that they additionally measure the radius of curvature of the posterior surface of the cornea and the thickness of the cornea and the optical power of the intraocular lens is determined by the formula:
$$D_{\mathrm{and}\mathrm{about}l}=\frac{1336\left(1336-L\frac{333}{R}\right)}{\left(L-p\right)\left(1336-p\frac{333}{R}\right)}$$

where Diol is the optical power of the intraocular lens, diopter;
L is the length of the eye, mm;
333 / R - standardized refraction of the cornea, diopters;
R is the radius of curvature of the anterior surface of the cornea, mm;
p is the distance between the front surface of the intraocular lens and the apex of the cornea after excimer laser keratectomy, mm, determined by the formula:
$$p=R_s-\sqrt{R_s^2-\frac{{\left(d-1.82\right)}^2}{\mathrm{four}}}+0.62467A+H-\mathrm{70,983}$$

R _s - the radius of curvature of the posterior surface of the cornea, mm;
A - constant A of the intraocular lens;
H is the thickness of the cornea in the center, mm;
d is the diameter of the cornea, mm.