RU2523153C1 - Method for measuring intraocular lens power with intracapsular fixation in pseudoexfoliation syndrome - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: eye length (L), curve radius of an anterior surface of the cornea (R), curve radius of a posterior surface of the cornea (R_P), the corneal diameter (d), as well as the maximum difference of lengths of the ciliary zonule fibres(S) and an intraocular lens constants A are measured. The intraocular lens power (Diol) is measured by formula: $$D_{iol}=\frac{1336\left(1336-L\frac{333}{R}\right)}{(L-p)\left(1336-p\frac{333}{R}\right)},$$

wherein 333/R is standardised corneal refraction, dptr. A distance from an anterior surface of the intraocular lens and an apex of the cornea in pseudoexfoliation syndrome (p) is determined by formula: $$p=R_P-\sqrt{R_P^2-\frac{{(d-\mathrm{1,82})}^2}{4}}+\mathrm{0,62467}A-\mathrm{70,563}-\mathrm{0,97}{e}^{-\mathrm{8,16}S}.$$

EFFECT: method enables providing more accurate measurement of the intraocular lens power with intracapsular fixation in pseudoexfoliation syndrome by taking into account the maximum difference of the lengths of the ciliary zonule fibres used for calculating the power value.

2 ex

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 of calculating the IOL for the eyes of patients with pseudoexfoliation syndrome, when there is a shift of the IOL towards the retina. 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 in pseudoexfoliation syndrome.

The technical result is achieved by the fact that in the method for determining the optical power of an intraocular lens with intracapsular fixation for pseudoexfoliation syndrome, 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, an additional measure is made of the maximum difference in the length of the fibers of the zinc ligament, and the optical power of the intraocular lens is determined by the formula:

$$D_{\mathrm{AND}\mathrm{ABOUT}L}=\frac{1336\left(1336-L\frac{333}{R}\right)}{(L-p)\left(1336-p\frac{333}{R}\right)}$$

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 with pseudoexfoliation syndrome, mm, determined by the formula:

$$p=R_s-\sqrt{R_s^2-\frac{{(d-1.82)}^2}{\mathrm{four}}}+0.62467\text{A-70}\text{, 563-0}{\text{, 97 e}}^{\text{-8}\text{, 16S}}$$

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

A - constant A of the intraocular lens;

S is the maximum difference in the length of the fibers of the zinc binder, 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, the value of the factory constant A of the intraocular lens and the value of the maximum difference of the fibers of the zinc ligament due to its weakening due to the pseudoexfoliation syndrome determined by the ultrasound method are taken into account.

In pseudo-exfoliative Zinn syndrome, the ligament is weakened and after intracapsular fixation of the IOL, its backward shift occurs. The value of hypermetropization increases with the severity of PES and a corresponding increase in the difference in the lengths of the fibers of the zinc binder. The displacement of the main plane of the IOL back is due to the following circumstances. Among the factors determining the stable position of the capsular bag with the implanted IOL, a certain role is played by the adhesion forces between the posterior capsule and the anterior hyaloid membrane of the vitreous body, which displace the capsular bag to the posterior pole of the eye. This shift is more pronounced when the fibers of the zinc ligament are weakened, which is characterized by the degree of PES. The higher the degree of PES, the higher the tendency to bias. Therefore, the determination of the distance between the front surface of the intraocular lens and the apex of the cornea according to the formula of the prototype due to this displacement gives underestimated 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 pseudoexfoliation syndrome, including measuring the length of the eye, the radius of curvature of the anterior surface of the cornea, the refraction of the cornea, the constant A of the intraocular lens, the maximum difference in the length of the fibers of the zinc ligament, the optical power of the intraocular lens is determined by the formula:

$$D_{\mathrm{AND}\mathrm{ABOUT}L}=\frac{1336\left(1336-L\frac{333}{R}\right)}{(L-p)\left(1336-p\frac{333}{R}\right)}$$

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 with pseudoexfoliation syndrome, mm, determined by the formula:

$$p=R_s-\sqrt{R_s^2-\frac{{(d-1.82)}^2}{\mathrm{four}}}+0.62467\text{A-70}\text{, 563-0}{\text{, 97 e}}^{\text{-8}\text{, 16S}}$$

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

A - constant A of the intraocular lens;

S is the maximum difference in the length of the fibers of the zinc binder, mm;

d is the diameter of the cornea, mm.

The method is illustrated by the following examples.

Example 1. Patient A., 56 years old. Diagnosis: Right eye - cataract with pseudoexfoliation syndrome of stage 3. According to the invention, the radius of curvature of the anterior surface of the cornea was measured: 7.8 mm, eye length: 23.60 mm, corneal diameter: 11.6 mm; radius of curvature of the posterior surface of the cornea: 6.9 mm; the maximum difference in the length of the fibers of the zinc binder 0.36 mm For implantation, an artificial lens model with a constant A of 118.2 was chosen.

Ophthalmoscan Model-200 from Sonometrics Systems Inc. was used to measure eye length. (USA), the radius of curvature of the anterior surface of the cornea - IOL-master (Germany), Pentacam HR Oculus (Germany), the maximum difference in the length of the fibers of the zinc binder was determined on a UBM-840 device from Humphrey (USA), the technological parameters of the IOL are indicated lens manufacturer in the product passport.

Substituting the measured values in the formula, according to the invention received: D _iol = 20.51 diopters.

An artificial lens with an optical power of 21.5 diopters was implanted.

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

Example 2. Patient Z., 66 years old. Diagnosis: Right eye - cataract with pseudoexfoliation syndrome of 4 degrees. According to the invention, the radius of curvature of the front surface of the cornea was measured: 7.92 mm, eye length: 24.12 mm, corneal diameter: 11.5 mm; radius of curvature of the posterior surface of the cornea: 7.06 mm. For implantation, an artificial lens model with a constant A of 118.2 was chosen.

Ophthalmoscan Model-200 from Sonometrics Systems Inc. was used to measure eye length. (USA), the radius of curvature of the anterior surface of the cornea - IOL-master (optical zone 2.5 mm) (Germany), the ultrasonic density of the zinc bond was determined using a Pentacam HR Oculus device (Germany), the 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 = 19.55 diopters.

An artificial lens with an optical power of 19.5 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 in pseudoexfoliation syndrome for the correction of 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 in pseudoexfoliation syndrome.

Claims (1)

A method for determining the optical power of an intraocular lens with intracapsular fixation in pseudoexfoliation syndrome, 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 also measure the maximum difference in the length of the fibers of the zinc cords, and the optical power lenses are determined by the formula:
$$D_{\mathrm{AND}\mathrm{ABOUT}L}=\frac{1336\left(1336-L\frac{333}{R}\right)}{(L-p)\left(1336-p\frac{333}{R}\right)}$$

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 with pseudoexfoliation syndrome, mm, determined by the formula:
$$p=R_s-\sqrt{R_s^2-\frac{{(d-1.82)}^2}{\mathrm{four}}}+0.62467\text{A-70}\text{, 563-0}{\text{, 97 e}}^{\text{-8}\text{, 16S}}$$

R _s - the radius of curvature of the posterior surface of the cornea, mm;
A - constant A of the intraocular lens;
S is the maximum difference in the length of the fibers of the zinc binder, mm;
d is the diameter of the cornea, mm.