Astigmatism Correction With Toric Intraocular Lenses
The reduction in refractive astigmatism after cataract surgery can result in a significant improvement in visual quality. Toric IOLs are an important option for decreasing astigmatism, giving predictable results and increasing the chance of spectacle independence postoperatively.
In our study we found that postoperative UDVA, optical quality in terms of MTFA/D and the Strehl ratio, and quality of life were better in the astigmatic patients implanted with toric IOLs in comparison with astigmatic patients implanted with non-toric spherical IOLs. These postoperative values in the toric group were similar to those in the non-astigmatic control group.
The significantly better refractive cylinder correction in the toric group compared with the astigmatic SN60AT group was indicated by the lower postoperative astigmatism. The lower astigmatism likely resulted in better statistical and clinical postoperative UDVA in the toric group.
The importance of wavefront evaluation for toric IOL implantation has been reported previously. Nevertheless, to our knowledge, this is the first report of a correlation between aberrometric results and subjective satisfaction assessed by the NEI-RQL 42 questionnaire in astigmatic patients implanted with toric IOLs. Statistical gains in objective visual quality were seen in the toric group, indicated by the increase in MTF A/D and Strehl ratio postoperatively, reaching postoperative values similar to patients with no preexisting corneal astigmatism. However, the confounding effects of neural processing cause ambiguity regarding the validity of objective measures in representing subjective patient impression. In the current study, we addressed this conundrum by administering a standardised well reported patient questionnaire (the NEI-RQL 42). The results of the NEI-RQL 42 questionnaire indicated significantly better postoperative visual quality perceived by the toric group compared with the control group in terms of glare symptoms, clarity of vision, far vision and satisfaction with correction.
Regarding the quality of life evaluation, a possible flaw in our study is the unilaterality of the surgery; however, our patients had a bilateral cataract, and a sensible change in life quality could be obtained even after one eye surgery.
The ability of the OPD Scan II to separate the anterior corneal surface from the internal aberrations allows determination of the source of refractive astigmatism preoperatively. Postoperatively, alignment of the toric IOL, residual astigmatism and induced aberrations can be evaluated using the various functions of this aberrometer/topographer combination. For example, retinal image quality can be separately analysed for cornea and crystalline lens or IOL.
In our clinical practice for toric IOL implantation, we prefer to examine the wavefront pattern of regular astigmatism (Z2, Z2) because the AcrySof toric IOL only corrects the regular astigmatism on the anterior corneal surface. However, evaluating visual performance with the MTF allows us to determine the effects of lower and higher order aberrations postoperatively.
In conclusion, the MTF and Strehl ratio data indicated gains in objective optical quality, retinal image quality and visual performance in eyes that underwent toric IOL implantation compared with eyes that underwent non- toric spherical IOL implantation, and this was likely related to reduced astigmatism in the toric group. The postoperative results in the toric group were similar to those in the non-astigmatic control group.
The NEI-RQL 42 instrument indicated better quality of life in eyes that underwent toric IOL implantation compared with eyes that underwent non-toric IOL implantation. This questionnaire is a sensitive subjective instrument that detects the visual benefits of toric IOLs and verified the results of the objective wavefront data.
In this study, we implanted spherical toric or non-toric IOLs. The benefits of aspheric IOLs on objective retinal image quality and quality of life have been documented previously. Because of these advantages, they are rapidly replacing monofocal spherical IOLs as the standard of care. Further studies are necessary to evaluate if the addition of the aspheric profile to toric IOLs will confer greater advantages.
Discussion
The reduction in refractive astigmatism after cataract surgery can result in a significant improvement in visual quality. Toric IOLs are an important option for decreasing astigmatism, giving predictable results and increasing the chance of spectacle independence postoperatively.
In our study we found that postoperative UDVA, optical quality in terms of MTFA/D and the Strehl ratio, and quality of life were better in the astigmatic patients implanted with toric IOLs in comparison with astigmatic patients implanted with non-toric spherical IOLs. These postoperative values in the toric group were similar to those in the non-astigmatic control group.
The significantly better refractive cylinder correction in the toric group compared with the astigmatic SN60AT group was indicated by the lower postoperative astigmatism. The lower astigmatism likely resulted in better statistical and clinical postoperative UDVA in the toric group.
The importance of wavefront evaluation for toric IOL implantation has been reported previously. Nevertheless, to our knowledge, this is the first report of a correlation between aberrometric results and subjective satisfaction assessed by the NEI-RQL 42 questionnaire in astigmatic patients implanted with toric IOLs. Statistical gains in objective visual quality were seen in the toric group, indicated by the increase in MTF A/D and Strehl ratio postoperatively, reaching postoperative values similar to patients with no preexisting corneal astigmatism. However, the confounding effects of neural processing cause ambiguity regarding the validity of objective measures in representing subjective patient impression. In the current study, we addressed this conundrum by administering a standardised well reported patient questionnaire (the NEI-RQL 42). The results of the NEI-RQL 42 questionnaire indicated significantly better postoperative visual quality perceived by the toric group compared with the control group in terms of glare symptoms, clarity of vision, far vision and satisfaction with correction.
Regarding the quality of life evaluation, a possible flaw in our study is the unilaterality of the surgery; however, our patients had a bilateral cataract, and a sensible change in life quality could be obtained even after one eye surgery.
The ability of the OPD Scan II to separate the anterior corneal surface from the internal aberrations allows determination of the source of refractive astigmatism preoperatively. Postoperatively, alignment of the toric IOL, residual astigmatism and induced aberrations can be evaluated using the various functions of this aberrometer/topographer combination. For example, retinal image quality can be separately analysed for cornea and crystalline lens or IOL.
In our clinical practice for toric IOL implantation, we prefer to examine the wavefront pattern of regular astigmatism (Z2, Z2) because the AcrySof toric IOL only corrects the regular astigmatism on the anterior corneal surface. However, evaluating visual performance with the MTF allows us to determine the effects of lower and higher order aberrations postoperatively.
In conclusion, the MTF and Strehl ratio data indicated gains in objective optical quality, retinal image quality and visual performance in eyes that underwent toric IOL implantation compared with eyes that underwent non- toric spherical IOL implantation, and this was likely related to reduced astigmatism in the toric group. The postoperative results in the toric group were similar to those in the non-astigmatic control group.
The NEI-RQL 42 instrument indicated better quality of life in eyes that underwent toric IOL implantation compared with eyes that underwent non-toric IOL implantation. This questionnaire is a sensitive subjective instrument that detects the visual benefits of toric IOLs and verified the results of the objective wavefront data.
In this study, we implanted spherical toric or non-toric IOLs. The benefits of aspheric IOLs on objective retinal image quality and quality of life have been documented previously. Because of these advantages, they are rapidly replacing monofocal spherical IOLs as the standard of care. Further studies are necessary to evaluate if the addition of the aspheric profile to toric IOLs will confer greater advantages.