Authors
Aymen Mdanat, FRCS, FRCOphth, Mousa Al-Madani, MD, Fahmi Aleikoor, FRCS(OPHTH)

Biconvex spherical surfaces create positive spherical aberration that is the peripheral rays comes to a shorter focus than central rays resulting in loss of contrast sensitivity¹. Traditional intraocular lenses are examples of those lenses that induce positive spherical aberrations.

Normally the cornea has positive spherical aberrations that offset the negative aberrations attributed to the lens². Small positive spherical aberrations allow greater depth of field. With aging, corneal aberrations increase and lenticular aberrations turn into positive, resulting in more positive spherical aberration and loss of contrast sensitivity. Negative spherical aberration lenses are recently used to offset the positive aberration of the cornea. They should be precisely positioned; otherwise high order aberrations such as coma will result³.

Aspheric advanced optics intraocular lenses have two aspheric surfaces to eliminate any spherical aberrations produced by the lens. The optic is asymmetrically biconvex with the anterior surface steeper than the posterior. The lens power is uniform throughout the optic surface, resulting in similar diffraction of peripheral and paraxial rays. They do not introduce new aberrations into the eye and closely follow the optics of phakic eye keeping small positive spherical aberrations with increased depth of field and good contrast sensitivity⁴.

In this study we aimed to evaluate the effectiveness of aspheric intraocular lenses in patients undergoing cataract phacoemulsification surgery. Some of our patients had a contralateral phacoemulsification cataract surgery with a traditional lens implant, which we compared with the recent surgery done.

This prospective and observational study was conducted at King Hussein Medical Center. Thirty patients who underwent phacoemulsification cataract surgery with implantation of an aspheric intraocular lens by the same surgeon, were examined. Inclusion criteria included patient's age between 50 and 85 years, intraocular lens power of 10-30 diopters and potential visual acuity 0.6 log MAR or better after surgery. Any patient with ocular pathology, central nervous abnormality or pre-operative complications affecting visual function was excluded from the study. Both high and low contrast visual acuities were evaluated using Log MAR visual acuity chart⁵. Patient satisfaction regarding surgery was graded as very satisfied where patients had no light related problem or glare at all; satisfied as having minor light related problem or glare; neutral, where no clear opinion was given; dissatisfied as having significant problems and very dissatisfied where they regretted having the operation.

SRK formula was used for intraocular lens calculation with target refraction ranging between -1.02 to zero. Patients were given the same standard pre-operative treatment of topical phenylephrine 10% drops and tropicamide 1% drops. Twenty eight patients had local anaesthesia (lidocaine 2% and bupivacaine 0.5%, 1:1 mixture) and 2 patients had general anaesthesia. All patients had clear corneal temporal incision of 3.00 mm. Capsulorrhexis was on optic and 5.0 mm on average. Surgery time ranged from 8 minutes to 23 minutes (15.2 minutes on average).

The age range was 50-78 years (mean 62.9 years) with 1.14:1 male to female ratio. Eleven patients had previous contralateral phacoemulsification cataract surgery with implantation of another type of intraocular lens.

Two third of patients had zero log MAR best corrected visual acuity and all patients had log MAR visual acuity = 0.2 at high contrast level of illumination. At low contrast illumination, seven patients (23.3%) had zero log MAR best corrected visual acuity (figure 1). 56.7% of the patients were very satisfied with the results of surgery and an additional 36.7% were satisfied. Only two patients were neutral and none of them were dissatisfied (figure 2). Among the eleven patients who had contralateral traditional implant, seven patients were more satisfied with aspheric variety and four patients found no difference. Four patients (36.4%) of the traditional implant group and two patients (6.7%) of the advanced optic group had light related problems. Increase in eye sensibility was found in 10% and unwanted images in 6.7% of the eyes with the aspheric intraocular lens and posterior capsular opacification occurred in one patient (table1).

Despite the importance of optical quality of an intraocular lens on visual outcomes following cataract surgery, objective data on their optical quality are not readily available, and manufacturing standards are industry regulated 6. Traditional implants are reported to cause light related discomfort in 33% of patients and driving problems in 40% ⁷. In our series, 36.4% and 27.3% of the traditional implant patients had such problems respectively.

Looking to figure one, we can see that 28 patients had log MAR best corrected visual acuity of less than 0.1 (corresponding to 6/9 Snellen's acuity) under high contrast illumination and that 26 patients had the same level of visual acuity under low illumination. The differences between these figures are not statistically significant but if we looked at the finest level of visual acuity (zero log MAR or 6/6 Snellen's acuity) the figures become significant (20 patients compared to 8, p<0.05). We can conclude that aspheric intraocular lenses are associated with the finest vision at high illumination level.

Regarding patient satisfaction, 93.3% of the advanced optic implants and 63.6% of the traditional implants were either very satisfied or satisfied. These results were statistically significant (p<0.05). If we look at the very satisfied group of patients, we find the results more significant (56.7% versus 9.1%, p<0.001).

Light related problems encountered in traditional implant groups were comparable to reported figures in literature⁷. In the advanced optic aspheric implant patients, less light related problems, driving problems, increased eye sensibility, and unwanted images were seen. All of these results except unwanted images were statistically significant (Table 1).

We followed the patients for 6 months after the operation, particularly looking for posterior capsular opacification; only one patient of the aspheric implant (3.3%) had posterior capsular opacification compared to two patients of the traditional implant group (18.2%).

The comparison between different types of implants in the same individual is associated with less subjective error than comparing two different groups of patients in terms of patient's satisfaction, and side effects encountered after surgery. Among the eleven patients who had contralateral traditional implant, seven patients were more satisfied with the aspheric implant and four patients found no difference.

Aspheric intraocular lenses are suitable for those with previously LASIK treatment, keratoconus, and other corneal aberrations⁸. They are designed with no variation in power from the center to the periphery providing predictable outcomes for all patients including those with zonular weakness or decentered pupils⁹. However, they should not be used in excessive preoperative corneal negative aberrations or post hyperopic LASIK where the traditional implants with the counteracting positive aberrations are advised.

The USA experience with aspheric lenses was that they resulted in better image quality, were more beneficial in young with larger pupils, and were minimally affected by decentration. The Italians found it to result in a dramatic decrease in posterior capsular opacification, more forgiving in cases of slight intraocular lens decentration and tilt and associated with better depth of field and less glare and dysphotopsia. The French experience was that they were associated with improvement of mesopic contrast sensitivity and had lower high order aberrations and fewer glares³.

In conclusion, aspheric intraocular lenses were associated with improvement of mesopic contrast sensitivity, better image quality and less glare. We advise to use them routinely in patients undergoing cataract phacoemulsification surgery except in cases of excessive preoperative negative corneal aberrations.

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Table 1 Side effects in relation to the type of intraocular lens.

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