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Пасечникова Н.В., Жабоедов Д.Г. Значение фактора сферичности и асферичности поверхности ИОЛ в создании качественных зрительных функций
02.08.2014, 17:11

Резюме
Пасечнікова Н.В., Жабоєдов Д.Г. Значення фактору сферичності та асферичності поверхні ІОЛ у створенні якісних зорових функцій.
З метою з’ясування значимості сферичного і асферичного дизайну оптичної частини ІОЛ для створення якісного зору при її імплантації проведено ретроспективний аналіз візуальних функцій в 91 випадку, серед яких 47 пацієнтам імплантували сферичну ІОЛ SА60AT, 44 – асферичну ІОЛ SN60WF. В обох групах отримані високі й якісні зорові функції, однак у пацієнтів зі сферичною лінзою показники аберацій, в тому числі аберацій вищих порядків, виявилися більшими порівняно з пацієнтами з асферичною ІОЛ. Встановлено, що компонент асферичності відіграє суттєву роль в покращенні якості зору особливо в умовах зниженої освітленості, тоді як у звичайних умовах різниця між групами не виявлена.
Ключові слова: факоемульсифікація катаракти, імплантація ІОЛ, сферичність і асферичність оптичної поверхні ІОЛ, якість зорових функцій.
Резюме
Пасечникова Н.В., Жабоедов Д.Г. Значение фактора сферичности и асферичности поверхности ИОЛ в создании качественных зрительных функций.
С целью уяснения значимости сферичного и асферичного дизайна оптической части ИОЛ для создания качественного зрения при ее имплантации проведен ретроспективный анализ визуальных функций в 91 случае, среди которых 47 пациентам имплантировалась сферичная ИОЛ SА60AT, 44 – асферичная ИОЛ SN60WF. В обеих группах получены высокие и качественные зрительные функции, однако у пациентов со сферической ИОЛ показатели аберраций, в том числе аберраций высших порядков, оказались больше по сравнению с пациентами с асферической ИОЛ. Установлено, что компонент асферичности играет заметную роль в улучшении качества зрения особенно в условиях пониженной освещенности, тогда как в обычных условиях разница между группами не выявлена.
Ключевые слова: факоэмульсификация катаракты, имплантация ИОЛ, сферичность и асферичность оптической поверхности ИОЛ, качество зрительных функций.

Summary
Pasechnikova N.V., Zhaboiedov D.G. Effect of sphericity and asphericity factor of iol optical surface on the visual functions quality.
 In order to clarify the significance of sphericity and asphericity of an IOL optical design in quality vision creation at its implantation it has been conducted the retrospective analysis of visual functions in 91 cases, of which 47 patients were implanted a spherical IOL SА60AT, 44 – an aspherical IOL SN60WF. Patients of both groups received high and qualitative visual functions, however in the group of patients with the spherical IOL indices of aberrations including high order aberrations were higher compare to patients with aspherical IOL implanted. It has been found that aspherical component plays a significant role in visual functions improvement especially in low light conditions whereas under normal conditions the differences between groups was not identified.
Key words: cataract phacoemulsification, IOL implantation, sphericity and asphericity of IOL optical surface, the quality of visual functions.

Рецензент: д.мед.н., проф. А.М. Петруня

УДК 617.7:681.42:535

 ГУ «Институт глазных болезней и тканевой терапии им. В.П.Филатова» (Одесса)

SI “The Filatov Institute of Eye Diseases and Tissue Therapy of the National Academy of Medical Sciences of Ukraine”  (Odessa)

Национальный медицинский университет им. А.А. Богомольца (Киев)

O.O. Bogomolets National medical university Kyiv

zhaboedov@ukr.net

Trends in the status of modern cataract surgery are shifting the focus attention of researchers from quantitative to qualitative characteristics of visual functions. Its improvement is achieved by reducing the trauma of the surgery on the eyeball itself and through the optimization of the constructive peculiarities of implanted intraocular lenses (IOL). In this, the development and improvement of IOL optics that reduces or eliminates spherical aberration (SA) of the pseudophakic eyes take the special place [2, 3].

It is known that under normal conditions, the passage of light rays through the optical media of the eye induces spherical aberration. Positive SA are generated by the cornea and the negative – by the lens that in the state of norm leads to its compensation. With age due to structural pathologic changes of the lens the part of positive SA increases resulting in reduction of visual acuity and contrast sensitivity in lower illumination condition especially with wide pupil. A similar situation is developing in the postoperative pseudophakic eyes in which light rays passing through the peripheral zone of the IOL are refracted more compare to paraxial that induces positive SA. Furthermore, IOL with high diopter due to convex profile of its optical surfaces also generates positive SA [6, 7, 9].

According to opinion of many researchers, implantation of IOL with optical aspherical design can significantly reduce or even eliminate SA of the entire optical system of the pseudophakic eye, which is an important condition for improving the quality of visual functions in patients after cataract surgery. At the same time, other authors note that subjective indicators of vision quality such as absolute visual acuity (VA) and contrast sensitivity is not significantly different from those of spherical lenses implantation [1, 4, 5, 8].

Thus, despite the obvious advantages of aspheric IOLs in terms of theoretical optics, some surgeons don’t note at the clinic significant differences in terms of VA and spatial contrast sensitivity (SCS) compared to conventional spherical IOL. Consequently, although the large variety of aspheric IOL models is introduced into practice of ophthalmic surgery, it is still a very debatable question the relationship of the optical characteristics of the lens with their clinical efficacy, which formed the basis for the study on the quality of the visual functions depending on the sphericity of the optical surface of the implanted IOL.

The purpose of the study – to clarify the importance of spherical and aspherical component of the IOL optical design in achieving the quality vision after cataract phacoemulsification.

Materials and methods. It has been conducted the retrospective analysis of visual functions after phacoemulsification of cataract (FEC) with IOL implantation in patients with uncomplicated cataract. This study included patients with pseudophakia – 91 eyes (100.0%), among which spherical IOL SA60AT were implanted in 47 cases (51.6%) – group 1, aspheric lenses SN60WF were implanted in 44 cases (48.4% ) – group 2. All operations were performed by the same surgeon with a same technology.

Before surgery, all patients underwent the ophthalmologic examination that included biomicroscopy, visiometry, auto refractometry, tonometry, ultrasound and optical biometry, ophthalmoscopy. IOL calculation were made by SRK/T formula. Postoperative follow-up after 3 months in addition to the above also included the investigation of spatial contrast sensitivity, aberrometry and focus depth measuring.

Results and discussion. Characteristics of the eyes are shown in Table 1. From the data it is visible that the distribution of the studied parameters in the groups was comparable.

Table 1

Characteristics of the studied patients groups (n=91)

Parameter

1 Group

2 Group

Quantity (eyes)

47 (51,6%)

44 (48,4%)

Age (years)

61,2±2,4

61,5±2,3

Gender (male/female)

23/24

21/23

Visual Acuity (with correction)

0,28±0,11

0,29±0,12

Keratometry before surgery (D)

43,51±1,4

43,49±1,2

Anteroposterior Axis (mm)

23,58±1,3

23,56±1,4

IOL power

22,31±0,9

22,76±1,12

 

In order to eliminate the influence of the refraction value on the depth of focus, eye refraction was equalized by correction of subjective indicators, for which the trial spectacle frames were used in condition of VA maximal correction for distance. Sequentially lens with variable optical power (in increments of ± 0,25 diopters) were inserted in a frame on the side of the test eye till the reduction of the maximum corrected VA for distance on the one line. Visual acuity for distance was measured with a maximum correction and VA for near and finite distance was measured without correction and with correction for distance (Table 2).

Table 2

Indices of Visual Acuity in patients with spherical and aspheric IOLs implanted in 3 months after cataract surgery

Patients Groups

VA for distance with maximal correction

VA for finite distance

VA for near

without correction

with correction for distance

without correction

with correction for distance

1

0,94±0,05

0,7±0,08

0,49±0,03

0,41±0,08

0,24±0,05

2

0,99±0,05

0,6±0,05

0,56±0,06

0,3±0,05

0,14±0,03

 

According to the data there are no significant differences in the corrected VA for distance between the groups, at the same time it was established significant difference between the groups in indices of VA for near with correction for distance (CfD). The highest VA for near vision with CfD (0,24 ± 0,05) and without correction (0,41 ± 0,08) was registered in group 1. In the same group 1 VA for finite distance with CfD and without correction was 0,49 ± 0,03 and 0,70 ± 0,08 respectively (vs. 0,56 ± 0,06 and 0,6 ± 0,05 in group 2).

Thus, the data from our study showed that after cataract surgery regardless to the sphericity design of implanted IOL VA of patients significantly improved, that confirms the results of other authors, and it was not identified significant differences in visual acuity for distance between the two groups with spherical and aspheric IOLs. This fact showed that all IOLs have the same capability to rehabilitation of VA for distance.

Keratometry data showed that the noticeable interdependence between refraction and sphericity or asphericity of implanted IOL was not found out.

In studying of aberrometry data it was paid the particular attention to high-order aberrations (HOA) of the entire eye (Entire Eye Aberrations) to the fourth order inclusive (Z4), and point spread function (PSF). Data are presented in a Table 3.

Table 3

Aberrometry data in 3 months after cataract surgery with IOL implantation

Data (μm)

Groups

1

2

Total aberrations

0,76±0,29* (0,71-0,86)

0,68±0,28* (0,57-0,86)

High-order aberrations

0,50±0,15* (0,48-0,52)

0,37±0,17* (0,36-0,40)

Spherical aberrations Z4

0,22±0,08* (0,25-0,28)

0,03±0,05* (0,03-0,06)

Coma

0,31±0,14* (0,27-0,31)

0,21±0,09* (0,17-0,21)

Vertical coma Z3-1

-0,16±0,19 (-0,18- -0,13)

0,04±0,17 (0,01-0,04)

Horizontal coma Z3+1

0,03±0,13 (0,01-0,05)

0,03±0,12 (0,01-0,03)

Trefoil

0,25±0,16* (0,23-0,26)

0,27±0,13 (0,19-0,21)

Trefoil Z3+3

0,06±0,11 (0,00-0,03)

-0,11±0,12 (-0,09-0,07)

Trefoil Z3-3

-0,11±0,09* (-0,13-0,11)

-0,17±0,13* (-0,19-0,13)

Focus Depth (D)

1,79±0,63*

1,39±0,65*

PSF (Strehl ratio)

0,31±0,11*

0,28±0,08*

Note.  *-р≤0,05.

It had been revealed a marked difference between the groups in total HOA as well as in certain types of aberrations, in particular, total aberrations are higher in group 1compare to group 2. SA (Z4) in the group with implanted spherical IOL were significantly higher. Total coma had  also higher values in group 1. A more detailed analysis of the coma showed that vertical coma (Z3-1) was significantly less in group 2. Values of the horizontal coma (Z3+1) did not differ between groups. In values of trefoil there was no significant differences between the groups. The difference in the value of the PSF (Strehl ratio) between the groups was not statistically significant.

The study established a significant difference in the depth of focus between the groups. In the group with a spherical IOL depth of focus was higher (1,79 ± 0,63), than the aspherical (1,39 ± 0,65). The depth of focus increasing in patients with implanted spherical IOL in our view can be explained by the fact that the spherical surface of the lens in the center and on the periphery of the optical part divides light stream into many separate focuses, that summing creates the effect of focus lengthening, however, due to this phenomenon image definition reduces, that subjectively noted by patients with spherical IOL implanted.

Correlation analysis revealed the key parameters of the wavefront affecting the VA for near and finite distance. In particular, we were able to establish that the total aberration, SA, HOA, coma, and the depth of focus are closely linked to VA for near and finite distance. It was determined a significant correlation between the total SA (r = 0,95, p <0,05), a simple coma (r = 94, p <0,05) and the depth of focus.

To assess visual function a study of contrast sensitivity was conducted, which was verified with a maximum spectacle correction in photopic and scotopic light conditions. These data confirmed that the aspherical component plays an important role in vision improving in low light conditions, whereas under normal conditions the difference between the two groups was not found.

Thus, the study of pseudophakic eye visual functions with implanted spherical or aspherical IOL showed that the quality of vision in each of these groups was sufficient high. Nevertheless, quantitative indices differences revealed inessential. It can be interpreted so that the final total effect depends on a large number of different factors, among which the importance of sphericity or asphericity of the IOL surface is masked, that makes it difficult to set clinical significance of the investigated phenomenon, especially that the impact of the corrective influence of brain visual centers is attached so it is not possible to isolate this due to lack of reliable methods for the psycho physiological effects studying. Though, it can be affirmed that there is a strong tendency towards improvement of visual quality produced by IOL aspherical design, that is evidenced by subjective sensations of patients with aspheric lenses implanted, which is difficult to express by specific numerical values.

Conclusions.

  1. Significant differences in visual acuity for distance without and with correction between patients with implanted spherical and aspheric IOLs were not identified.
  2. It was revealed the marked differences between the groups in the total HOA as well as in specific types of aberrations, in particular, total SA were higher in group 1 compare to group 2. The difference in the value of the PSF (Strehl ratio) between the groups was not statistically significant.
  3. IOL with spherical component significantly improves the depth of focus compare to aspherical IOL (p <0,05), however the details clarity of subjects is reduced.
  4. According to data of spatial contrast sensitivity it was determined that the aspherical component plays an important role in improving of vision especially in low light conditions, whereas under normal conditions the difference between the groups was not found.

Литература

  1. Владимиров Д.В. Сравнение результатов аберрометрии глаз после имплантации сферических и асферических интраокулярных линз / Д.В. Владимиров // Збірник наукових праць співробітників НМАПО імені П.Л. Шупика. – 2011. – Вип. 20, Кн. 1. – С. 463–469.
  2. Демьянченко С.К. Клинико-теоретическое обоснование метода интраокулярной коррекции афакии асферическими ИОЛ : дис. ... канд. мед. наук : 14.01.07 / Демьянченко Сергей Константинович; [Место защиты: ФГБУ «МНТК «Микрохирургия глаза» им. акад. С.Н. Фёдорова» Минздравсоцразвития России]. – М., 2011. – 83 с.: ил.
  3. Малюгин Б.Э. Современные стандарты хирургии катаракты с имплантацией интраокулярной линзы (обзор литературы) / Б.Э. Малюгин, А.В. Терещенко, Ю.А. Белый [и др.] // Рефракционная хирургия и офтальмология. – 2010. – Т. 10, № 3. – С. 4–10.
  4. Малюгин Б.Э. Сравнительная характеристика зрительных функций и данных аберрометрии у пациентов со сферической, асферической и аккомодирующей моделями ИОЛ / Б.Э. Малюгин, М.А. Исаев, А.В. Головин [и др.] // Офтальмохир. – 2012. – № 2. – С. 36–37.
  5. Awwad S.T. Contrast sensitivity and higher order aberrations in eyes implanted with Acrysof IQ SN60WF and AcrySof SN60AT intraocular lenses / S. T. Awwad, D. Warmerdam, R. W. Bowman, S. Dwarakanathan [et al.] // J. Cataract Refract. Surg. – 2008. – Vol. 24. – P. 619–625.
  6. Morales E.L. Comparison of optical aberrations and contrast sensitivity between aspheric and spherical intraocular lenses / E.L. Morales, K.M. Roha, M.R. Chalita [et al.] // J. Refract Surg. – 2011. – Vol. 27, № 10. – P. 723–728.
  7. Packer M. Aspheric intraocular lens selection based on corneal wavefront / M. Packer, I.H. Fine, R.S. Hoffman // J. Refract. Surg. – 2009. – Vol. 25, № 1. – P. 12–20.
  8. Trueb P.R. Visual acuity and contrast sensitivity in eyes implanted with aspheric and spherical intraocular lenses / P.R. Trueb, C. Albach, R. Montés-Micó, T. Ferrer-Blasco // Ophthalmology. – 2009. – Vol. 116 (5). – P. 890–895.
  9. Tzelikis P.F. Spherical aberration and contrast sensitivity in eyes implanted with aspheric and spherical intraocular lenses: a comparative study / P.F. Tzelikis, L. Akaishi, F.C. Trindade [et al.] // Am. J. Ophthalmol. – 2008. – Vol. 145. – Р. 827–833.
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