RU2675398C1 - Method of measurement of the thickness of a lens with diffuse opacities of a nucleus and cortical layers - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: invention relates to ophthalmology and can be used to measure the thickness of the lens with diffuse opacities of the nucleus and cortical layers. Conduct ultrasonic immersion A-biometrics. Average ultrasonic wave velocity of 1,629 m/s is used. Distance between the amplitudes of the A-echo signal from the front to the back surface of the lens is determined. Posterior border of the lens with diffuse opacities is determined with the installation and activation of the "Gate" function to localize the posterior lens capsule on the echogram.

EFFECT: method allows the most accurate calculation of the optical power of an IOL implanted after cataract phacoemulsification, by using an ultrasonic wave velocity of 1,629 m/s.

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Description

The invention relates to ophthalmology and is intended to measure the thickness of the lens (TX) in patients with mature cataract before surgery in order to most accurately calculate the optical power of the IOL.

It is known that the Barrett Universal II formula is the most accurate modern formula for calculating the optical power of an intraocular lens (IOL), which takes into account the patient's TX [Jack X. Kane, Anton Van Heerden, Alp Atik ,, Constantinos Petsoglou. Accuracy of 3 new methods for intraocular lens power selection // J Cataract Refract Surg. - 2017. Vol. - 43 (3). P. 333 - 339]; [Olga Reitblat, Adi Levy, Guy Kleinmann, Tsahi T. Lerman, Ehud I. Assia. Intraocular lens power calculation for eyes with high and low average keratometry readings: Comparison between various formulas // J Cataract Refract Surg. - 2017. Vol. - 43 (9). P. 1149-1156]; [David L. Cooke, Timothy L. Cooke. Comparison of 9 intraocular lens power calculation formulas // J Cataract Refract Surg. - 2016. Vol. - 42 (8). P. 1157-1164].

Currently, optical biometry remains the most reliable method for measuring TX GN. John Shammas, Maya S. Shammas. Measuring the cataractous lens // J Cataract Refract Surg. - 2015. Vol. - 41 (9). P. 1875-1879], however, its use is limited by the technical capabilities of the devices and reducing the transparency of the optical media of the eye. In addition, there is a direct relationship between the occurrence of lens opacities, an increase in cataract density and a decrease in the accuracy of calculating the optical power of the IOL [Ueda TI, Taketani F., Ota T, Hara Y. Impact of nuclear cataract density on postoperative refractive outcome: IOL Master versus ultrasound / / Ophthalmologica - 2007. Vol. 221 (6). P. 384-387].

A universal method for determining TX in all patients, regardless of the state of the optical media of the eye, is ultrasound biometry. Measurement can be carried out both by contact and immersion methods. The contact method of A ultrasound imaging is widespread in ophthalmic practice, however, its accuracy is limited by the resolution of the device, the echo signal from the cornea is localized in the "dead zone" of the sensor. The accuracy and reproducibility of immersion biometric data is significantly higher compared to the contact method due to the fixation of the sensor in the Prager nozzle and the presence of an immersion medium between the sensor and the cornea [Michael P Hennessy, Derek G Chan. Contact versus immersion biometry of axial length before cataract surgery // J Cataract Refract Surg. - 2003. Vol. - 29 (11). P. 2195-2198].

S.T. Fontana and R.F. Brubaker found that the average value of TX is 4.01 mm for children 1 year old and 4.8 mm for people over 80 years old [S.T. Fontana, R.F. Brubaker. Volume and depth of the anterior chamber in the normal aging human eye // Arch Ophthalmol. - 1980. Vol. - 98. P. 1803-1808]. G. Bellows proposed to determine TX by the formula: 4+ value of the patient's age, expressed in hundredths. For example, according to the formula, in a patient at 52 years of age, TX should be 4.52 mm [G. Bellows. Cataract and anomalies of the lens: growth, structure, composition, metabolism, development, growth disorders and treatment of the crystalline Lens // St Louis, MO, CV Mosby. - 1944. P. 60-86].

In addition, the speed of the ultrasonic wave varies as the cataract ripens. A change in the speed of ultrasound in the lens by 50 m / s leads to an average error in calculating the optical power of the IOL up to 0.5 Dptr [G.L. Vanderheijde, J. Weber. Accommodation used to determine ultrasound velocity in the human lens // Optom Vis Sci. 1989. - Vol. 66 (12) - P. 830-833].

In published works, the results of measuring the speed of an ultrasonic wave in a clouded lens are variable. D.J. Coleman et al. In 1975 conducted a study of 4 eyes in children and 50 eyes in adult patients with cataracts and determined that the rate of ultrasonic wave velocity in the lens is on average 1659 m / s at the age of 1 year and reaches a value of 1629 m / s to 72 years. [D.J. Coleman, F.L. Lizzi, L.A. Franzen, D.H. Abramson A Determination of the velocity of ultrasound in cataractous lenses. // Ultrasonography in Ophthalmology. - Bibl. Ophthalmol. 1975 .-- Vol. 83. P. 246-251]. In 1962, F. Jansson and E. Kock obtained an average ultrasound velocity of 1640.5 m / s, with 1641 m / s for young people in a clear crystalline lens, 1628 m / s for an initial clouding, and mature cataract - 1589 m / s, however, this study included a total of 12 eyes [F. Jansson, E. Kock. Determination of the velocity of ultrasound in the human lens and vitreous. // Acta Ophthalmol. 1962. - 40. - P. 420-433]. D.J. Coleman et al. Published data in 1975 in which the velocity of an ultrasonic wave in a mature cataract was 1670 m / s. [D.J. Coleman, F.L. Lizzi, R.L. Jack Ultrasonography of the Eye and Orbit. Philadelphia: Lea &Febiger; 1977]

The closest analogue of the invention is a method of measuring the thickness of the lens with opacities using the standard method of ultrasonic immersion A - biometry [Renu Jivrajka, Maya C. Shammas, Teresa Boenzi, Mike Swearingen, H. John Shammas. Variability of axial length, anterior chamber depth, and lens thickness in the cataractous eye // J Cataract Refract Surg. - 2008. Vol. - 34 (2). P. 289-294]. The measurement of PZO and TX eyes with transparent lenses, as well as eyes with initial and posterior capsular cataracts, is carried out in the standard “Phackic” mode, which implies the use of the known ultrasonic wave propagation velocity in the lens - 1641 m / s. In patients with dense cataracts and diffuse opacities of the lens, the measurement is performed in the “Dens cataract” mode, which uses a standard TX value of 4.7 mm without taking into account the speed of propagation of the ultrasonic wave velocity in the lens. Thus, despite the development of ultrasonic and optical methods of biometry, the issue of accurate measurement of TX in patients with mature cataracts still remains an issue.

The task of the invention is to develop a more accurate ultrasound determination of the thickness of the lens with diffuse opacities of the nucleus and cortical layers.

The technical result of the proposed method is the possibility of the most accurate calculation of the optical power of the IOL implanted after cataract phacoemulsification.

The technical result is achieved by performing immersion A-biometry using an ultrasonic wave velocity of 1629 m / s and determining the posterior border of the lens with diffuse opacities with the setting of a mark when the “Gate” function is activated to localize the posterior lens capsule on the echogram.

We conducted a study in which we determined the optimal value of the ultrasonic wave velocity for the biometrics of a clouded lens. We measured PZO and TX in patients with mature swelling cataract (36 eyes) using various diagnostic modes of the ultrasound scan. First, immersion A-scan of the eyes was performed in the standard “Phakic” mode, the PZO and TX measurements were performed, then the same parameters were determined after the “Gate” function was activated and the echo signal of the posterior lens capsule was localized. Secondly, the measurement of PZO and TX was carried out in the "Dens cataract" mode recommended by manufacturers of ultrasound equipment for use in patients with mature cataract. Thirdly, after we created the “Dense cataract new” mode, in which the ultrasonic wave velocities for a clouded lens 1589 m / s, 1629 m / s, 1670 m / s were used sequentially, the values of PZO and TX were determined. The results of biometrics are presented in Table 1.

Note:

* - the ultrasonic scanning modes developed by us with the speed of an ultrasonic wave for measuring TX 1589 m / s, 1629 m / s and 1670 m / s

** - differences are statistically significant (p <0.05)

“Gate” + - the “Gate” function is activated, measurements are taken taking into account the localization of the signal from the posterior lens capsule.

“Gate” - - the “Gate” function is not activated, measurements were taken without taking into account the localization of the signal from the posterior lens capsule.

There were no statistically significant differences between the obtained PZO values during immersion A-biometry using all the above-described modes (p> 0.05), despite clinically significant differences between the values using the Gate function and without it. Statistically significant differences were found between the results of measuring TX without activating the “Gate” function and with it. The propagation velocity of an ultrasonic wave in a swelling lens is variable, however, the measurements of TX obtained using a value of 1629 m / s turned out to be identical to those used in the "Dense cataract" mode and amounted to 4.69 ± 0.25 and 4.7 ± 0.0, respectively . Therefore, the “Dense cataract new” mode with an ultrasonic wave velocity for measuring TX equal to 1629 m / s is most suitable for measuring TX in patients with mature swelling cataract, using the values of 1589 m / s and 1670 m / s for biometrics . The physical properties of ultrasound also suggest a decrease in the speed of the ultrasonic wave as structural changes of the swelling lens increase.

Therefore, to accurately measure the thickness of the lens in a patient with mature swelling cataracts by ultrasound, the “Gate” function should be activated and the ultrasonic wave velocity used to measure the thickness of the lens equal to 1629 m / s.

Thus, we have developed a new “Dense cataract new” mode (Fig. 1 - “Dense cataract new” mode, when conducting A-scan, the ultrasound speed for a cloudy lens was set to 1629 m / s), taking into account the average ultrasound speed of 1629 m / c for a lens with diffuse opacities, which is optimal and corresponds to the morphological changes of the dense lens against the background of mature cataract. A method for determining TX during mature cataract includes immersion ultrasound A-biometry with obtaining the highest possible echo signals from the cornea, anterior and posterior surfaces of the lens, retina and sclera, followed by a decrease in amplitude of the echocomplex of signals from retrobulbar fiber in a developed mode that takes into account the average speed of the ultrasonic wave in clouded lens equal to 1629 m / s, with further determination of the distance between the amplitudes A - of the echo signal from the front to the back surface of the crystal This is the installation and activation of the “Gate” function on the echogram.

The method is as follows.

In a patient with diffuse opacities of the nucleus and cortical layers, ultrasound immersion A-biometry is performed. Using the average speed of the ultrasonic wave, equal to 1629 m / s, determine the distance between the amplitudes of the A-echo signal from the front to the back surface of the lens, while the posterior border of the lens with diffuse opacities is determined by setting and activating the “Gate” function to localize the posterior lens capsule on the echogram .

Clinical example.

Patient K., 49 years old. Upon receipt of the visual acuity of the left eye - 0.02 n / a, failed to perform autorefractometry. The results of keratometry of the left eye according to the IOL-Master device were: R1 - 44.87 Dptr ah 45 °; R2 - 44.37 Dptr ax 135 °; cyl -0.5 Dptr ah 5 °, ACD - 2.7 mm, WTW - 12.0 mm. Pneumotonometry - 17 mm Hg. When conducting ultrasound in the vitreous body, floating opacities were visualized, the posterior detachment of the vitreous body; retinal detachment was not detected. An objective examination: the eye was calm, the anterior chamber was smaller than average (2.7 mm), destruction of the pigment rim of the iris of 1-2 tbsp., Pronounced diffuse opacities of the lens were revealed. According to the survey, the diagnosis was made: mature cataract of the left eye. Scheduled phacoemulsification of cataracts of the left eye. When performing an A-scan of the eyeball in the “Phakic” mode without activating the “Gate” function, the TX was 3.43 mm, and the PZO was 23.65 mm. (Fig. 2 - A-scan of the eyeball in patient K., 49 years old with mature cataract: “Phakic” mode, “Gate” function for the posterior lens capsule is not activated, the lens thickness is 3.43 mm).

When using the “Gate” function in the “Phakic” mode, the lens thickness was 5.58 mm, the PZD was 23.79 mm, which is 0.14 mm more than in the previous measurement (Fig. 3 - A-scan of the eyeball in the patient K., 49 years old with mature cataract: “Phakic” mode, the “Gate” function for the posterior lens capsule is activated, the thickness of the lens is 5.58 mm). In the "Dense cataract" mode, the lens thickness is not measured, since a standard value of 4.7 mm is used, the PZO value is 23.74 mm (Fig. 4 - A-scan of the eyeball in patient K., 49 years old with mature cataract: mode "Dense cataract", the thickness of the lens is standard - 4.7 mm;). Thus, the measurement of biometric parameters of the eye in patients with mature cataract in the Phakic mode using the speed for an optically transparent lens of 1641 m / s is not correct. The use of the Dense cataract new regime allowed the most accurate measurement of both TX (5.54 mm) and eye length (23.75 mm) in a patient with mature cataract. (Fig. 5 - A-scan of the eyeball in patient K., 49 years old with mature cataract: “Dence cataract new” mode, the “Gate” function for the posterior lens capsule is activated, the lens thickness is 5.54 mm.) those obtained in the Dense cataract and Dense cataract new modes turned out to be almost the same, 23.74 and 23.75, respectively. In FIG. 6 (A-scan of the eyeball in patient K., 49 years old with mature cataract: in the “Dens cataract new” mode, the ultrasonic wave speed for the mature lens is set at 1670 m / s, the “Gate” function for the posterior lens capsule is activated, the lens thickness is 5.68 mm, PZO 23.89) presents an A-scan of the left eyeball in the "Dense cataract new" mode at a set ultrasonic wave speed for the mature lens equal to 1670 m / s (Fig. 7 - "Dense cataract new" mode, when conducting A-scan, the ultrasound speed value for a cloudy lens was established - 1670 m / s), the “Gate” function for the posterior lens capsule was activated, the TX was 5.68 mm, the PZO was 23.89, which clearly shows the differences from the obtained values when applying the “Dense cataract new” mode with the speed of the ultrasonic wave for clouded lens 1629 m / s.

Based on the obtained data, the IOL was calculated using the Barrett Universal II formula; the obtained optical power value of the Domilens Nidek NS-60YG Aktis SP IOL was +19.0 Dptr when calculating for emmetropia (the calculated value of the spheroequivalent of postoperative refraction is -0.26 Dptr). The next day, the patient's maximum uncorrected visual acuity was 0.9, after 1 week - 1.0.

Thus, the proposed method provides an increase in the informational content of TX measurement for the accurate calculation of IOL in patients with mature cataract due to immersion A-biometry of the eye, taking into account changes in the speed of the ultrasonic wave in a dense clouded lens, which is one of the main aspects of achieving refraction of the target after surgical treatment cataracts.

Claims (1)

A method for measuring the thickness of a crystalline lens with diffuse opacities of the nucleus and cortical layers by performing ultrasound immersion A-biometry, characterized in that the average ultrasonic wave velocity of 1629 m / s is used, the distance between the amplitudes of the A-echo signal from the front to the back surface of the lens is determined, In this case, the posterior border of the lens with diffuse opacities is determined with the installation and activation of the “Gate” function to localize the posterior lens capsule on the echogram.

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