Comparison of visual quality between aspheric and spherical IOLs

Ramazan Yagc?1 , Feyza Uzun2 , Semra Acer1 , Ibrahim F. Hepsen2. 1School of Medicine, Department of Ophthalmology, Pamukkale University, Denizli - Turkey. 2School of Medicine, Department of Ophthalmology, Fatih University, Ankara - Turkey.

Purpose: To determine if aspheric intraocular lens (IOL) implantation produces the same degree of postoperative ocular aberration and contrast sensitivity as spherical IOL implantation.

Methods: In this randomized prospective comparative study, 60 eyes of 30 cataract surgery patients were randomly assigned to receive a spherical IOL (Rayner 620H) in one eye and an aspheric IOL (Rayner 920H) in the contralateral eye. All patients were examined at 1 month postoperatively. Primary outcomes of contrast sensitivity and ocular wavefront higher order aberrations (HOAs) were assessed.

Results: Aspheric IOLs (median total HOAs 0.26 root mean square [RMS]; range 0.13-0.82 RMS) produced significantly lower total HOAs than spherical IOLs (median total HOAs 0.34 RMS; range 0.18-1.08 RMS; p<0.05). Contrast sensitivity was significantly better with aspheric IOLs (median contrast sensitivity 1.8 log units; range 1.35-1.8 log units) than with spherical IOLs (median contrast sensitivity 1.65 log units; range 1.35-1.8 log units; p<0.05).

Conclusions: When compared with a structurally (platform and material) similar spherical IOL (Rayner 620H), aspheric IOLs (Rayner 920H) appear to significantly reduce HOAs and yield better levels of contrast sensitivity under photopic conditions.

Keywords: Asphericity, Cataract surgery, Intraocular lens, Wavefront aberration

Accepted: February 5, 2014

INTRODUCTION

The goal of cataract surgery is no longer limited to the restoration of good visual acuity; most surgeons now aim to provide their patients with the best visual quality possible (1). The maximization of visual quality—objectively assessed via contrast sensitivity measurement or wavefront aberrometry—is a key focus of new aspheric intraocular lens (IOL) designs (2). Such designs aim to minimize the effects of age-related contrast sensitivity loss, known to arise from an age-related increase in positive aberrations originating from the natural lens (3-5).

Aspheric IOLs produce fewer positive spherical corneal aberrations than conventional spherical IOLs, and as such, produce better contrast sensitivity and visual acuity (4). However, the mode of aspheric IOL action is dependent on the type of aspheric IOL implanted. Zero-aberration aspheric IOLs have no impact on preexisting spherical aberrations, whereas negative aberration aspheric IOLs offset positive corneal spherical aberrations to produce aberration-free images (6, 7).

Previous research has shown that the presence of positive spherical aberrations increases depth of focus and that depth of focus is positively associated with perceived visual quality (8). Thus, negative aberration lenses—which cancel out all positive aberrations—may produce poorer subjective visual quality than aberration-free IOLs, despite providing optimal contrast sensitivity. Studies such as that by Nochez et al (9) illustrate that a final postoperative outcome that has small residual amounts of natural positive spherical aberration (between 0.07 and 0.10 μm) ensures optimal perceived and measurable visual quality, i.e., optimal depth of focus and contrast sensitivity.

In this prospective study, we aimed to compare the levels of ocular aberrations and contrast sensitivity achieved with implantation of the Rayner 920H aspheric aberration-neutral IOL and the Rayner 620H spherical acrylic IOL in patients undergoing bilateral cataract surgery.

This is the first study in which visual quality outcomes have been compared following the implantation of an aspheric aberration-neutral Rayner IOL in one eye and a spherical Rayner IOL made with the same material in the other eye.

MATERIALS AND METHODS

This prospective randomized study involved patients undergoing bilateral cataract removal via phacoemulsification between May 2010 and April 2011. All surgery was performed at Fatih University Hospital, Ankara, Turkey. The tenets of the Declaration of Helsinki were followed. Patients were implanted with an aspheric IOL Rayner 920H in one eye and a spherical IOL Rayner 620H in the fellow eye. The eye implanted with the aspheric IOL was chosen at random for each patient. Rayner IOLs are single-piece lenses composed of foldable hydrophilic acrylic material (refractive index, 1.46) with an overall length of 12.5 mm and optic diameter of 6.25 mm. Patients with visually significant bilateral cataract and corneal astigmatism lower than 2.0 D were eligible for inclusion in the study. Exclusion criteria included the presence of surgical complications or any ocular disease, such as corneal opacities or irregularity, amblyopia, anisometropia, glaucoma, or retinal abnormalities. All patients underwent contrast sensitivity, distance best-corrected visual acuity (BCVA), and wavefront aberrometry measurements at 30 days after surgery.

We carried out corneal and ocular wavefront analysis with the Galilei anterior segment topographer (Galilei, Ziemer, Port, Switzerland, software version 5.2.1) and Schwind aberrometer (Schwind, Eyetech Solutions, Kleinostham, Germany, software version 3.1.3.751), which uses Hartmann-Shack technology to obtain wavefront data. No dilating eyedrops were used during wavefront measurements and the root mean square (RMS) of aberrations was calculated.

The Hamilton-Veale contrast sensitivity test was performed at the same visit. The test is modeled on the Pelli-Robson contrast sensitivity test and was conducted at 33.3 cm from the subject, using a card measuring 30 × 20 cm and consisting of 8 rows of letters, divided into 16 blocks with 2 letters in each block. The contrast used in the test varied from black on white (level 1) to nearly white on white (level 16). The letters were the same size as a 20/200, 6/60, or logMAR 1.0 letter, which corresponds to a spatial frequency of 1 cycle per degree.

Absolute values of log contrast sensitivity were obtained for each eye under a recommended illumination of 60-120 cd/m2 . We chose the Hamilton-Veale chart for contrast sensitivity measurement because this was quick to carry out in a clinical setting and was the only contrast sensitivity chart available in the hospital at which the surgery was performed.

We performed all surgery under topical anesthesia using a conventional phacoemulsification technique. The technique involved the creation of a 2.8-mm clear corneal incision, a 5.0-5.5 mm anterior continuous curvilinear capsulorhexis, extracapsular cataract extraction by phacoemulsification, and in-the-bag IOL implantation with an injector system. No sutures were used in any case. Postoperative medications included topical moxifloxacin 0.5% and dexamethasone 0.1% eyedrops 4 times daily for 1 month. Patients had sequential surgery 1 week apart.

Statistical analyses were performed using Microsoft Excel 2003 and SPSS for Windows version 15.0 (SPSS Inc., Chicago, Illinois, USA) software. We used the Shapiro-Wilk test and graphical analysis to test the normality of continuous data. Descriptive statistics were expressed as numbers for categorical variables and mean ± standard deviation for normally distributed continuous variables. Median and interquartile range values were expressed for skewed data. The χ2 test was used for categorical data analysis, the independent samples t test was used for evaluation of numerical parameters with normal distribution, and the Mann-Whitney test was used for evaluation of parameters without normal distribution. Statistical significance was defined as a p value of at least 0.05.

All applicable institutional and governmental regulations concerning the ethical use of human volunteers were followed during this research.

RESULTS

We evaluated 60 eyes of 30 patients (21 women, 70%). The patients had a mean age of 68.12 ± 8.2 years (SD). No intraoperative complications, defined as zonule or posterior capsule rupture, vitreous loss, or capsulorhexis tear, or posterior capsule opacification were identified. A postoperative slit-lamp examination showed well-centered IOLs in the capsular bag in all eyes with no cases of clinically significant decentration.

The mean BCVA achieved following aspheric IOL implantation was greater than that achieved with spherical IOL implantation (p = 0.002). Preoperative and postoperative corneal wavefront aberrations measurements revealed no difference in total higher order aberration (HOA) RMS. Measurements captured during ocular wavefront aberrometry showed significantly lower spherical aberration values (p = 0.003) and total HOAs (p = 0.002) for the aspheric IOL group than for the spherical IOL group. No significant difference was seen for horizontal and vertical coma RMS (p = 0.249 and p = 0.310, respectively). Contrast sensitivity was significantly better with the aspheric IOL than with the spherical IOL (p<0.001) (Tab. I)

DISCUSSION

Recent advances in IOL design have involved the application of wavefront technology to improve optical efficiency and visual function. The ability to measure HOAs has led to a better understanding of the eye as an optical system and the development of aspheric IOLs.

In this study, we compared a hydrophilic acrylic aspheric IOL (Rayner 920H) and a hydrophilic acrylic spherical IOL (Rayner 620H). Rayner 920H and Rayner 620H IOLs are made of a similar material and platform, resulting in similar physical and anatomic outcomes. By choosing IOLs made by the same manufacturer and of the same material, we were able to evaluate the effect of optical asphericity on the level of visual quality provided by the IOL, while minimizing potential confounding factors. We evaluated BCVA and visual function determined by contrast sensitivity and HOA.

Several previous studies with a similar aim have not identified statistically significant differences in the BCVA achieved with aspheric versus spherical IOL implantation (10-15). Other studies, however, have demonstrated better BCVA in eyes implanted with an aspheric IOL compared with eyes with a spherical IOL (7, 16, 17). Our study findings show a significantly better mean BCVA following aspheric versus spherical Rayner IOL implantation.

Contrast sensitivity function, which plots the reciprocal of the threshold contrast for sinusoidal gratings as a function of their spatial frequency, is a visual performance index that accurately reflects human spatial vision. It gives information on visual performance for a range of object scales (2). Numerous studies designed to evaluate photopic contrast sensitivity have identified significantly better outcomes with aspheric than spherical IOLs (11, 14, 17-19); other studies, however, have found no significant differences in visual outcomes with each lens type (5, 12, 20-22). Such discrepant findings emphasize the uncertainty that surrounds the specific outcomes achievable with aspheric IOLs under photopic conditions. It is important to keep in mind that the methods used to measure contrast sensitivity varied between the different studies and may not have been sensitive enough to detect potentially significant differences in contrast vision under photopic or mesopic conditions (2, 15, 23, 24). Thiagarajan et al (7) measured photopic contrast sensitivity using a Pelli-Robson chart and found no significant difference in contrast sensitivity achieved with aspheric and spherical IOL groups. Conversely, Santhiago et al (15) detected better performance with aspheric IOLs than with spherical IOLs, with Pelli-Robson contrast sensitivity testing under photopic conditions. Our study findings also showed that a significantly better photopic contrast sensitivity was achieved with aspheric than spherical IOL implantation.

Our findings are in keeping with those of other studies that have compared negative-aberration aspheric IOLs with spherical IOLs. These studies showed that lower levels of spherical aberration occur with the former IOL type (25- 28). Caporossi et al (11) conducted a study in which an aberration-free aspheric IOL, the Sofport AO (Bausch & Lomb, Inc., Rochester, New York, USA), was compared with a spherical IOL. Their findings showed lower values of spherical aberration with the aspheric IOL. Johansson and associates (8) compared the aspheric IOL, Akreos AO (Bausch & Lomb, Inc.), with the aspheric IOL, Tecnis (Abbott Medical Optics Inc., Abbott Park, Illinois, USA), and found that the Tecnis produced significantly lower values of spherical aberration than the Akreos. Nabh and associates (29) compared 3 aspheric IOLs (Akreos AO, Tecnis, and AcrySof IQ) and found lower values of spherical aberration in eyes implanted with the AcrySof IQ than in eyes implanted with the Akreos AO; however, the Akreos AO group had lower values of spherical aberration than the aspheric IOL Tecnis group. In our study, eyes implanted with the aspheric IOL Rayner 920H showed lower values of spherical aberrations and total HOAs than eyes implanted with the spherical IOL Rayner 620H. These results reflect those of previous studies. The difference in preoperative and postoperative corneal total HOA between the 2 groups was not statistically significant. These results indicate that the reduction in ocular spherical aberration was mainly caused by implantation of the aspheric IOLs. Dietze and Cox (30) suggested that more coma aberration is induced when an aspheric IOL is decentered. In the current study, postoperative ocular coma was taken as a measure of the degree of IOL decentration and tilt in the capsular bag. There was no statistically significant difference in coma values between the aspheric and spherical IOL groups. It is possible that our lower levels of coma aberration justify the lower decentration in both IOL groups.

A limitation of this study was the failure to measure contrast sensitivity under mesopic conditions. Pupils are larger under mesopic conditions and pupil size is positively associated with spherical aberration quantity. The reduction of ocular spherical aberrations may lead to improvements in contrast sensitivity, and therefore testing visual quality under mesopic conditions may help to determine if aspheric IOLs lead to a significant decrease in spherical aberrations. In conclusion, the findings of our study suggest that hydrophilic acrylic aspheric Rayner 920H IOL implantation yields significantly lower ocular wavefront aberration and better contrast sensitivity than the spherical Rayner 620H IOL implantation. The aspheric Rayner IOL may therefore be considered an effective method of maximizing a patient’s optical quality after cataract surgery. Further largescale studies examining functional visual quality after IOL implantation are necessary.

Financial Support: No financial support was received for this submission.

Conflict of Interest Statement: None of the authors has conflict of interest with this submission.

Meeting Presentation: Presented at the 29th Congress of the ESCRS, Vienna, Austria, September 2011.

Address for correspondence: Ramazan Yagc?

Department of Ophthalmology

Pamukkale University Hospital

Camlaralti M. Universite C

20070 Kinikli Denizli

Turkey

[email protected]

REFERENCES

1. Morales EL, Rocha KM, Chalita MR, Nosé W, Avila MP. Comparison of optical aberrations and contrast sensitivity between aspheric and spherical intraocular lenses. J Refract Surg 2011;27:723-8.

2. Montés-Micó R, Ferrer-Blasco T, Cervi?o A. Analysis of the possible benefits of aspheric intraocular lenses: review of the literature. J Cataract Refract Surg 2009;35:172-81.

3. Artal P, Berrio E, Guirao A, Piers P. Contribution of the cornea and internal surfaces to the change of ocular aberrations with age. J Opt Soc Am A Opt Image Sci Vis 2002;19:137-43.

4. Su PY, Hu FR. Intraindividual comparison of functional vision and higher order aberrations after implantation of aspheric and spherical intraocular lenses. J Refract Surg 2009;25:265-72.

5. Kurz S, Krummenauer F, Thieme H, Dick HB. Contrast sensitivity after implantation of a spherical versus an aspherical intraocular lens in biaxial microincision cataract surgery. J Cataract Refract Surg 2007;33:393-400.

6. Nio YK, Jansonius NM, Geraghty E, Norrby S, Kooijman AC. Effect of intraocular lens implantation on visual acuity, contrast sensitivity, and depth of focus. J Cataract Refract Surg 2003;29:2073-81.

7. Thiagarajan M, McClenaghan R, Anderson DF. Comparison of visual performance with an aspheric intraocular lens and a spherical intraocular lens. J Cataract Refract Surg 2011;37:1993-2000.

8. Johansson B, Sundelin S, Wikberg-Matsson A, Unsbo P, Behndig A. Visual and optical performance of the Akreos Adapt Advanced Optics and Tecnis Z9000 intraocular lenses: Swedish multicenter study. J Cataract Refract Surg 2007;33:1565-72.

9. Nochez Y, Majzoub S, Pisella PJ. Effect of residual ocular spherical aberration on objective and subjective quality of vision in pseudophakic eyes. J Cataract Refract Surg 2011;37:1076-81.

10. Rocha KM, Soriano ES, Chamon W, Chalita MR, Nosé W. Spherical aberration and depth of focus in eyes implanted with aspheric and spherical intraocular lenses: a prospective randomized study. Ophthalmology 2007;114:2050-4.

11. Caporossi A, Martone G, Casprini F, Rapisarda L. Prospective randomized study of clinical performance of 3 aspheric and 2 spherical intraocular lenses in 250 eyes. J Refract Surg 2007;23:639-48.

12. Sandoval HP, Fernández de Castro LE, Vroman DT, Solomon KD. Comparison of visual outcomes, photopic contrast sensitivity, wavefront analysis, and patient satisfaction following cataract extraction and IOL implantation: aspheric vs spherical acrylic lenses. Eye 2008;22:1469-75.

13. Ohtani S, Miyata K, Samejima T, Honbou M, Oshika T. Intraindividual comparison of aspherical and spherical intraocular lenses of same material and platform. Ophthalmology 2009;116:896-901.

14. Assaf A, Kotb A. Ocular aberrations and visual performance with an aspheric single-piece intraocular lens: contralateral comparative study. J Cataract Refract Surg 2010;36:1536-42.

15. Santhiago MR, Netto MV, Barreto J Jr, et al. Wavefront analysis, contrast sensitivity, and depth of focus after cataract surgery with aspherical intraocular lens implantation. Am J Ophthalmol 2010;149:383-9.

16. Mester U, Dillinger P, Anterist N. Impact of a modified optic design on visual function: clinical comparative study. J Cataract Refract Surg 2003;29:652-60.

17. Bellucci R, Scialdone A, Buratto L, et al. Visual acuity and contrast sensitivity comparison between Tecnis and AcrySof SA60AT intraocular lenses: a multicenter randomized study. J Cataract Refract Surg 2005;31:712-7.

18. Pandita D, Raj SM, Vasavada VA, Vasavada VA, Kazi NS, Vasavada AR. Contrast sensitivity and glare disability after implantation of AcrySof IQ Natural aspherical intraocular lens: prospective randomized masked clinical trial. J Cataract Refract Surg 2007;33:603-10.

19. Mester U, Kaymak H. Comparison of the AcrySof IQ aspheric blue light filter and the AcrySof SA60AT intraocular lenses. J Refract Surg 2008;24:817-25.

20. Denoyer A, Le Lez ML, Majzoub S, Pisella PJ. Quality of vision after cataract surgery after Tecnis Z9000 intraocular lens implantation: effect of contrast sensitivity and wavefront aberration improvements on the quality of daily vision. J Cataract Refract Surg 2007;33:210-6.

21. Kasper T, Bühren J, Kohnen T. Visual performance of aspherical and spherical intraocular lenses: intraindividual comparison of visual acuity, contrast sensitivity, and higher order aberrations. J Cataract Refract Surg 2006;32:2022-9.

22. Awwad ST, Warmerdam D, Bowman RW, Dwarakanathan S, Cavanagh HD, McCulley JP. Contrast sensitivity and higher order aberrations in eyes implanted with AcrySof IQ SN60WF and AcrySof SN60AT intraocular lenses. J Refract Surg 2008;24:619-25.

23. Dick HB. Recent developments in aspheric intraocular lenses. Curr Opin Ophthalmol 2009;20:25-32.

24. Ginsburg AP. Contrast sensitivity and functional vision. Int Ophthalmol Clin 2003;43:5-15.

25. Kasper T, Bühren J, Kohnen T. Intraindividual comparison of higher-order aberrations after implantation of aspherical and spherical intraocular lenses as a function of pupil diameter. J Cataract Refract Surg 2006;32:78-84.

26. Marcos S, Barbero S, Jiménez-Alfaro I. Optical quality and depth-of-field of eyes implanted with spherical and aspheric intraocular lenses. J Refract Surg 2005;21:223-35.

27. Rocha KM, Soriano ES, Chalita MR, et al. Wavefront analysis and contrast sensitivity of aspheric and spherical intraocular lenses: a randomized prospective study. Am J Ophthalmol 2006;142:750-6.

28. Bellucci R, Morselli S, Piers P. Comparison of wavefront aberrations and optical quality of eyes implanted with five different intraocular lenses. J Refract Surg 2004;20:297-306.

29. Nabh R, Ram J, Pandav SS, Gupta A. Visual performance and contrast sensitivity after phacoemulsification with implantation of aspheric foldable intraocular lenses. J Cataract Refract Surg 2009;35:347-53.

30. Dietze HH, Cox MJ. Limitations of correcting spherical aberration with aspheric intraocular lenses. J Refract Surg 2005;21:S541-6.