Reduced wavefront aberration influence the visual function after the senile cataract surgery with an aspherical intraocular lens

Purpose: To evaluate whether the aspherical intraocular lens (IOL) with a modified aspherical anterior surface provides better quality of vision than the conventional spherical IOL for the senile cataract patients after phacoemusification and IOL implantation.

Methods: Consecutively 115 eyes were selected from 72 senile cataract patients who received phacoemulsification and IOL implantation in Peking University Eye Center, age range from 49 to 84(63.9±9.9 years old).Each was randomly assigned to receive TecnisZ9001 IOL or CeeOnEdge 911 and or Sensar AR40e (both made by AMO). In the time frame from one day before operation, one week, one month, three months and six months after operation, the eyes underwent several checkups by the same personnel. checkups included visual acuity, optometry, contrast sensitivity test and wavefront aberration (WA) examination. The parameters included best corrective visual acuity, the values of contrast sensitivity, Z40 Zernike coefficient, root mean square of the 4th order (RMS4) and higher-order root mean square (RMSh). Visual functional questionnaires were finished and the scores were saved. Then statistical analysis needs to be done.

Results: Spherical wavefront aberration has positive correlation with the age (r=0.582, P value<0.05). There are no significant difference of BCVA between each two of the three groups before or after the operation (P value>0.05). The patients with Tecnis IOL get lower Z40 Zernike coefficient, RMS4 and the RMSh than these items in the CeeOn 911 group and Sensar AR40e group(P value<0.05), and higher contrast sensitivity at the 5 level of spatial frequency. Furthermore, the visual function scores are higher than the other two spherical IOL group (P value<0.05).

Conclusion: The older of the patient, the higher spherical wavefront of the eye would be. Different from the conventional spherical IOL, a kind of aspherical IOL can provide better quality of vision by reducing the spherical wavefront after cataract surgery.

Key Words: Intraocular lens, aberration, cataract, visual function

Corresponding author: Wei Wang,

The human eyes are not ideal optical devices. In theory, size and space differences of photoreceptor cells make it possible for the retinal resolution to reach 3.0[1,2] . Due to the existence of wavefront aberration which limits the visual quality, BCVA can only reach 2.0 or lower. Despite conventional refractive surgeries do make corrections with satisfying postoperative vision, many patients complain about the syndrome and side-effects associated with the surgery, such as dizzying, selaphobia, lowered contrast sensitivity, blurred vision in dark environment etc. Research has found that the postoperative vision weakening is related to the increase of higher-order aberration. Study of wavefront aberration of the human eyes, especially higher-order aberrations, is something new that was developed in recent years. Its clinical application mainly reflects in refractive surgeries that are driven by wavefront aberration. In clinical terms, the aberrations are occasioned by cornea and lens. Along with aging, the aberration also grows. If spherical IOLs are implanted in a cataract surgery, positive aberration may still occur, which will not eliminate corneal aberration. The emerging intraocular lens, however, results in negative spherical aberration. With special treatments to the anterior/posterior chambers of the corneal lens, corneal refractivity will be reduced and therefore it compensates the positive corneal aberration.

Our research focuses on comparing differences between spherical and aspherical IOL to patients’ visual function after senile cataract surgery, especially emphasizing on the study of postoperative spherical aberrations. Results from objective and subjective observations are carefully studied. Other parameters, including the best corrective visual acuity, the values of contrast sensitivity and questionnaires collecting results of patients’ vision after surgery, are all applied in the analysis of our research.

1. Objects & Methodology

1.1 Objects of Study

From February to December 2005, 72 patients diagnosed cataract by and treated in the Peking University Eye Center with a total of 115 eyes were the major objects of the study. Among them, 43 patients received cataract surgeries on both eyes. For statistics and figures please refer to Table1. As our research requires a keen cooperation from the patients in postoperative checkups on parameters such as the values of contrast sensitivity, the result of subjective aberration checkups, the patients’ occupation, education level, therefore, matters. Such results from follow-up checkups as a matter of fact play a key role in weighting our study. After analyzing the characteristics and traits of the clan of our patients, with our Eye Center’s geographic location and surrounding habitant composition in mind, we narrowed down our research participates to those who mostly were retiree teachers and governmental officers as this clan of patients normally enjoy a relatively higher education level. We also invited retirees who would like to cooperate with us on after-surgery follow-ups. Due to limited resources of our Eye Center, however, we cannot guarantee a completely random-chosen mechanism in terms of pinning down each patient. We tried our best to assure the continuity of our cases. Detailed screening criterion please refers to in the following Participants chosen criterion (1.4) and the principle that same IOL should be used on both eyes on a single patient applies throughout our research.

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Table 1. Case scenario TecnisZ9001，CeeOn911and Sensar materials are used in three groups of patients respectively with participants’ age range between 49-84 years-old, average 63.9 years-old, in line with the mathematical approach as normal distribution.

1.2 Research Material

1.2.1 Intraocular lens

- TecnisZ9001, AMO（Advanced Medical Optics）(US firm)
- CeeOn Edge911, AMO (US firm)
- Sensar AR40e, AMO (US firm)

1.2.2 Devices

- Standard logarithmic vision chart and Jaeger vision chart
- FACT test card for the measuring of contrast sensitivity
- Noncontact tonometer: Canon, Tonometer TX-10
- Cornea curvimeter: Nikon，Speedy-K
- counts of corneal endothelium，Iconan， Nonconrobo Pachy
- A-type ultrasonic device: Alcon， The Ultrascan Imaging System
- corneal keratometer，Zeiss, WaveLight, Allegro Topolyzer
- Subjective wave-front aberrometer: WFA1000 from Suzhou Liangjing Medical Equipment Co., ltd
- Objective wavefront aberrometer: Zeiss, WaveLight, Allegretto Wave Analyzer
- Sovereign phacoemulsification instrument: AMO Co., ltd USA

1.3 Methodology

1.3.1 Checkups before-surgery include ：

- Uncorrected far/near visual acuity
- Standard optometry, best corrective and uncorrective visual acuity
- Tonometer: 3 consecutive measures should be taken using Tonometer TX-10 noncontact tonometer, high and low margins are balanced within 3mm range, the mean should be taken
- Rountain slit lamp and fundus examination;
- Corneal diopter measures: Speedy-K diopter measuring device should be used with the parameter of 12mm，high and low margins are indicated as K1 and K2 respectively; the high point and low point are used in the calculation of IOL modeling;
- Counts of corneal endothelium cells: Nonconrobo Pachy non-contact device should be used: cell density on the medium, on point-3 and point-9 should be recorded together with the percentage of hexagonal cell;
- Axial length measuring: 10MHz A-type device should be used, result will be used in determining IOL;
- Corneal topology test: Allegro Topolyzer should be used to exam lesions other than ailments on the corneal curvature and keratoconus etc.
- Subjective aberration test: WFA1000 Subjective aberration measuring device should be used, the patient should conduct such tests on themselves. Method will be taught to the patients and three times of tests should be observed for the best result;
- Objective wavefront aberration test: Allegretto Wave Analyzer objective aberration testing device should be used; Mydriatic eye drop should be used on the sick eye(s) 10min/doses ×3～5 doses; 10 minutes after the last dose when the diameter of the pupil is larger than 6.0mm, an objective aberration test should be conducted. All such tests should be conducted by the same person with at least 4 times of each tests done so on the same eye so as to screen out one best result that satisfies the following criterions: 1) lowest dispersion value between the lower-order aberration (myopic astigmatism) and the optometry result; 2) best match of the high-order aberration graph and the root mean square; 3) best focus of the original photo; 4) lest dislocation from the center. The focal point of our research is the result of objective wavefront aberration. Thanks to the software studying condition of the eye, we can observe various level of aberrations occurred in different miotic conditions (with different pupil diameters)

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