|Year : 2019 | Volume
| Issue : 2 | Page : 158-164
Anatomical and functional outcomes of toric intraocular lens implantation
Dubbaka Srujana, Dattakiran Joshi, Amit Sethi, Sriharsha Lanka, Roopali Y Bhirud, Robin Malik
Department of Ophthalmology, INHS Asvini, Mumbai, Maharashtra, India
|Date of Submission||10-Apr-2019|
|Date of Acceptance||05-Jun-2019|
|Date of Web Publication||07-Oct-2019|
Air Cmde (Dr) Dattakiran Joshi
Department of Ophthalmology, INHS Asvini, Mumbai - 400 005
Source of Support: None, Conflict of Interest: None
Background: To minimize the residual refractive correction, toric intraocular lens (TIOL) is being increasingly used in cases undergoing cataract surgery with preexisting corneal astigmatism of ≥1.0 D. Aims: The aim of this study is to evaluate anatomical and functional outcomes of TIOL implantation in cases undergoing cataract surgery with significant corneal astigmatism using conventional manual marking of target axis and to see for any difference in outcomes based on the power of TIOL. Methodology: It is a prospective observational study. Consecutive patients with cataract and astigmatism of >1.0 D with adequate pupil dilation and no significant ocular or systemic comorbidity scheduled to undergo phacoemulsification with TIOL implantation were enrolled. Results: The mean improvement in postoperative uncorrected distance visual acuity (UDVA) over preoperative corrected distance visual acuity was 0.51 ± 0.54 logarithm of the minimum angle of resolution (95% confidence interval CI: 0.30–0.70), equivalent to 4 Snellen lines. The mean postoperative spherical equivalent is 0.38 ± 0.27; 77.4% showed within 0.50 D and the rest were within 1 D. The mean deviation of postoperative TIOL alignment from intended intraoperative TIOL alignment is 3° ± 2° (range: 0°–6°). Both the groups (low- and medium-power TIOLs) had similar postoperative UDVA, residual astigmatism, and deviation of target axis. Conclusions: There was an effective correction of preoperative corneal astigmatism and good visual outcomes with TIOL implantation. Fairly accurate TIOL alignment is achievable with manual marking of target axis. The power of TIOL did not influence postoperative UDVA, residual astigmatism, or deviation of TIOL from target axis.
Keywords: Alignment, astigmatism, cataract surgery, toric intraocular lens
|How to cite this article:|
Srujana D, Joshi D, Sethi A, Lanka S, Bhirud RY, Malik R. Anatomical and functional outcomes of toric intraocular lens implantation. J Mar Med Soc 2019;21:158-64
| Introduction|| |
Modern-day cataract surgery has undergone a stupendous transformation from a mere removal of cataractous lens to the present-day smaller incision phacoemulsification with foldable intraocular lens to achieve least possible residual refraction. Newer advances have enabled us to tackle corneal astigmatism ensuring better refractive outcomes. In cases undergoing cataract surgery, preoperative corneal astigmatism of 1 D or more may be present in up to one-third of cases with 22% having >1.5 D of astigmatism and 8% having >2.0 D of astigmatism.,, Not addressing this astigmatism can result in a significant residual refraction postcataract surgery leading to a considerably reduced unaided visual acuity. Various techniques such as limbal relaxing incisions and opposite clear corneal incisions have been described to decrease corneal astigmatism at the time of cataract surgery. However, the results are unpredictable due to variations in surgical technique, corneal thickness, scarring response, and regression of achieved refraction over a period of time. Toric intraocular lens (TIOL) implantation has been introduced with a view to neutralize corneal astigmatism by providing a toric refracting surface on the IOL. Since its introduction in 1992 by Shimizu et al. as a three-piece nonfoldable polymethyl methacrylate implant inserted through a 5.7-mm incision, TIOL has come a long way to the present-day foldable acrylic hydrophobic TIOL which can be implanted through a 2.2-mm incision. Correct alignment of the axis of TIOL is very important for good postoperative visual outcomes. Various methods have been in practice to mark the target axis for TIOL alignment from conventional manual marking to image-guided systems of Callisto eye with Z align ® and Verion ®. Although a more accurate alignment of the TIOL has been reported with the image-guided systems as compared to conventional manual marking methods, the visual outcomes are comparable.,,
This study has been conducted to evaluate anatomical and functional outcomes with the implantation of modern TIOLs in cases undergoing cataract surgery with significant corneal astigmatism. Furthermore, we tried to see whether manual marking technique still holds a place in this era of more expensive image-guided systems in terms of desired TIOL alignment and visual outcomes. In addition, there is limited literature available on outcomes of low-power TIOL versus medium-power TIOL; hence, we endeavored to see in our study for any difference in TIOL outcomes based on their power.
| Methodology|| |
This was a prospective observational study conducted at a tertiary care center. Ethical clearance was obtained from the Institutional Review Board. Written informed consent was obtained from all the patients. The study conforms to the tenets of the Declaration of Helsinki. Consecutive patients with cataract and astigmatism of >1.0 D scheduled to undergo phacoemulsification with TIOL implantation from November 2018 to January 2019 were enrolled in the study. Eyes with pupil dilation of at least 5.0 mm, regular astigmatism ranging from 1.0 to 6 D, and no significant ocular or systemic comorbidity were included. Eyes with preexisting retinal pathology, small pupils (<5 mm), significant corneal opacity, irregular astigmatism, ocular surface disorders, history of contact lens usage, and previous corneal/intraocular/refractive surgery were excluded. A total of 31 patients fulfilled the inclusion criteria and have constituted the study population.
A comprehensive ocular examination was done which included uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), slit-lamp biomicroscopy, fundus examination, noncontact tonometry, and optical biometry with Zeiss IOLMaster 500 (Carl Zeiss AG, Jena, Germany) to measure axial length (AL) and keratometry to determine corneal astigmatism. The emmetropic IOL spherical power was calculated after feeding the A-constant of the TIOL (Tecnis Toric Aspheric IOL; AMO, Illinois, USA) into the IOL Master. The best of five repeat AL measurements (with a minimum signal-to-noise ratio of 2.0) and the mean of three sets of keratometry measurements were selected for IOL power calculations. Biometry was repeated if the inter-eye AL difference was found to be > 0.3 mm. If AL was not possible to measure with IOL Master due to mature cataract or thick posterior subcapsular cataract, a scan was used and the best of five measurements with good spikes was taken. As per the standard practice, the required spherical lens power was first determined with IOL Master using SRK/T formula (Hoffer Q formula was used for eyes with AL < 22 mm). Following this, the final spherocylinder which needs to be corrected by the TIOL was taken as the sum of the keratometry values from IOL Master and the surgically induced astigmatism (SIA) spherocylinder. SIA of the surgeon was calculated previously using Dr. Warren Hill's SIA calculator. TIOL power and orientation were chosen using the manufacturers' online calculators, which took into account AL, keratometry values, and surgeon-induced astigmatism.
Preoperatively, the reference axis was marked at 3, 6, and 9'o clock positions using the bubble marker (Nuijts Lane Toric Reference Marker) with the patient positioned erect and maintaining a straight-ahead gaze. Intraoperatively, the reference limbal marks were aligned to the degree gauge on the fixation ring (Mendez Gauge), and the target axis was marked with a two-ray axis marker inked with marking ink. Furthermore, the main corneal incision was marked as per the toric calculation sheet. A 2.8-mm clear corneal incision and two 1.1-mm side port incisions were made. Anterior continuous curvilinear capsulorhexis of ~5 mm was made with a 26G needle cystotome. Coaxial phacoemulsification (with Stellaris; Bausch and Lomb.) was performed, and TIOL (Tecnis Toric Aspheric IOL; AMO, Illinois, USA) was implanted in the bag. The IOL was rotated to align with the target axis and was kept about 5° anticlockwise. After completion of irrigation, aspiration, and meticulous removal of ophthalmic viscosurgical device (OVD) including from behind the IOL, TIOL alignment was completed and stromal hydration of the corneal incisions was performed. Postoperatively, all the patients received 0.5% moxifloxacin eye drops four times a day for 2 weeks 1% prednisolone eye drops four times a day for 3 weeks which was tapered over next 3 weeks and were reviewed at 1 day, 3 days, 10 days, 3 weeks, and 6 weeks. Postoperative IOL orientation was seen and measured on slit lamp using a thin vertical slit on day 1 and at 6 weeks [Figure 1]. Postoperative UDVA, CDVA, refraction, and keratometry using IOL Master were recorded at 6 weeks.
|Figure 1: Postoperative assessment of toric intraocular lens implantation axis on slit lamp|
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Outcome measures were postoperative visual acuities (unaided and best-corrected), refractive astigmatism, spherical equivalent (SE) (obtained either by manifest refraction or by autorefraction), reduction in total astigmatism, residual corneal astigmatism, and deviation of TIOL alignment from target axis. Further, eyes were assigned to two groups as per the toric power of the TIOL. Group 1 included low-power TIOLs (Tecnis Toric Aspheric IOL ZCT +1, +2.25; AMO, Illinois, USA) and Group 2 comprised patients receiving medium-power TIOLs (Tecnis Toric Aspheric IOL ZCT +3, +3.75, +4.5; AMO, Illinois, USA). Statistical analysis was performed using SPSS software SPSS for Windows, version 17.0 (SPSS Inc., Released 2008, Chicago, IL, USA).
| Results|| |
Thirty-one eyes of 29 patients (19 females and 10 males) with a mean age of 63.7 years (standard deviation: 9.9, range: 37–80) were included in the study [Table 1]. All 31 eyes received Tecnis Toric Aspheric IOL. The preoperative corneal astigmatism was against the rule (ATR) in 67.7% (n = 21), with the rule (WTR) in 29% (n = 9), and oblique astigmatism was seen in 3.2% (n = 1). Group 1 consisted of 12 eyes with low-power TIOL and the rest 19 eyes received medium-power TIOL in Group 2. There were no general cataract surgery-related complications, such as posterior capsule rupture, zonular dialysis, or endophthalmitis. More importantly, there was no significant TIOL rotation which required IOL repositioning. In the 31 eyes that received TIOLs, 30 eyes (96.77%) achieved an improvement in postoperative UDVA compared with the preoperative CDVA, 1 eye (0.03%) showed no change, and none of the eyes showed reduction. The mean improvement in postoperative UDVA over preoperative CDVA was 0.51 ± 0.54 logarithm of the minimum angle of resolution (logMAR) units (95% confidence interval: 0.30–0.70) [Table 2]a and [Table 2]b, equivalent to 4 Snellen lines. The postoperative logMAR UDVA ranged from 0.00 to 0.48 with a mean of 0.24 ± 0.11. In the one eye that showed no change in postoperative UDVA from preoperative CDVA, 1.00 D of residual cylinder was found with a SE of 0.25 and the visual acuity (0.48 logMAR) improved to 0.07 logMAR with correction. The mean postoperative SE is 0.38 ± 0.27. In terms of postoperative SE, 24 eyes (77.4%) showed within 0.50 D and the rest 7 eyes were within 1 D. The preoperative mean corneal astigmatism (ΔK) was 2.1 D ± 0.68. The preoperative refractive cylinder could be obtained only in 14 cases as the rest of them had either thicker posterior subcapsular cataract or denser cataracts including hypermature cataract. For those 14 cases, the mean preoperative refractive cylinder was 2.29 DC ± 0.77. The postoperative mean refractive cylinder was 0.65 DC ± 0.24, and the mean reduction of postoperative cylinder over preoperative mean ΔK is 1.46 ± 0.69 representing a statistically significant reduction (P < 0.0001) [Table 3]a and [Table 2]b. All 31 eyes (100%) showed a reduction in refractive cylindrical correction. There was a decrease in corneal astigmatism postoperatively, although this difference was not significant (2.1 ± 0.68 vs. 1.76 ± 0.79, P= 0.07). The mean difference of postoperative TIOL alignment from intended intraoperative TIOL alignment is 3° ± 2° (range: 0°–6°). In cases with ATR astigmatism, this misalignment was 2.62° ± 2.13° and it was slightly more in WTR astigmatism cases 4° ± 1.41°; however, the difference is not statistically significant (P = 0.09). In 5 eyes, the postoperative IOL alignment was exactly the same as was placed during surgery and all of them were seen in ATR cases.
The preoperative characteristics of the two groups were similar [Table 4]. The mean corneal astigmatism was 1.75 ± 0.46 D (1.30–2.74) in Group 1 versus 2.32 ± 0.72 D (1.32–3.67) in Group 2, which was consistent with the choice of TIOLs; however, this difference was not statistically significant (P > 0.05). The mean AL was 22.8 ± 1.1 mm (range: 20.33–24.58) with no statistically significant difference between the two groups. The comparison of postoperative data is shown in [Table 5]. No patients required a postoperative IOL adjustment. The mean postoperative UDVA was similar in the two groups: 0.22 logMAR in Group 1 versus 0.24 logMAR in Group 2 (P = 0.39). There was a statistically significant difference in postoperative CDVA between the two groups, and Group 2 with mean CDVA of 0.06 logMAR had one case with preexisting corneal opacity with CDVA of 0.3 logMAR and four patients of 0.18 logMAR attributable to amblyopia of which three had preoperative corneal astigmatism of >3.0 D. The mean residual refractive astigmatism was 0.56 D in Group 1 and 0.7 D in Group 2 (P = 0.11). The distribution of preoperative corneal astigmatism and residual postoperative refractive cylinders of the groups is shown in [Figure 2] and [Figure 3]. 100% of the patients in Group 1 achieved ≤0.75 D of residual cylinder as compared to 57.9% in Group 2. In our study group, none of the eyes suffered an increase in refractive astigmatism after TIOL implantation. The reduction of the refractive astigmatism was highly significant in both the groups. The postoperative SE was not statistically different in the two groups (0.39 vs. 0.42, P= 0.7). 77.4% of the eyes achieved a SE within ± 0.5 D, 75% of the eyes in Group 1 and 78.9% in Group 2. The mean reduction of corneal astigmatism was 0.47 D ± 0.56 in Group 1 and 0.26 D ± 0.62 in Group 2 which was not statistically significant (P = 0.35). The mean deviation in IOL alignment at 6 weeks postoperative from the intended intraoperative alignment is similar in both the groups (2.75° vs. 3.92°, P= 0.3).
|Figure 2: Preoperative astigmatism and postoperative refractive cylinder in low-power toric intraocular lens implantation group|
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|Figure 3: Preoperative astigmatism and postoperative refractive cylinder in medium-power toric intraocular lens implantation group|
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| Discussion|| |
To obtain optimal visual outcomes in TIOL implantation, it is important to accurately align the TIOL along the target axis. Various modalities both manual and image-guided modalities are in use for this purpose. The three-step manual marking techniques conventionally used have given fairly accurate alignment of TIOL with a mean deviation from target axis of 4.9° ±2.1°. Recently, with the introduction of the image-guided systems and intraoperative aberrometry, there has been an improvement in the precision of TIOL alignment, with <5° of deviation from the intended axis in the majority of cases.,, Titiyal et al. compared Callisto eye and Z align ® with manual marking techniques; a mean deviation of <5° was achieved with Callisto eye and Z align ®, whereas it was >5° with manual marking. In our study, manual marking with bubble marker, fixation ring, and two-ray marker has been used to mark the target axis. The deviation from target axis in our study was 3° ± 2° (range: 0°–6°) which was similar to the results obtained with image-guided systems and aberrometry. Despite the subjective nature of manual marking, optimal results can be achieved if adequate diligence is followed while marking, as has been shown in this study. Various other variables that have contributed to a reasonably accurate target axis achievement postoperatively are the hydrophobic nature of the TIOL used with adequate overall diameter, adequate coverage of optic of TIOL by the anterior capsule, and meticulous removal of OVD including from behind the IOL, and none of the eyes were of high AL, all of them providing better rotational stability of TIOL.,
In our study, 20/40 or better was achieved in 93.5% (29 out of 31) of cases which is comparable with various studies which have shown a postoperative UDVA of 20/40 or better achieved in 70%–100% of cases undergoing TIOL implantation.,,, Holland et al. in a randomized control trial observed residual astigmatism of 1.0 D or less in 88% of cases and 0.5 D or less in 53% of cases undergoing TIOL implantation. Our study showed residual astigmatism of 1.0 D or less in 100% of cases and 0.50 D or less in 45.2% of cases (14 out of 31).
It has been reported that 1° of misalignment of TIOL axis causes a loss of approximately 3% of the effective cylinder power, and the entire toric effect is lost with induction of cylinder in a new meridian in cases with 30° of misalignment., TIOL is required to be realigned if there is >10° of rotation from the target axis. In cases where the deviation from target axis is <10°, the manifest refraction changes only by 0.5 D and hence does not require any additional intervention. Further, it is seen that realignment may be required in 0.65%–3.3% of cases, 1.1% with AcrySof TIOL, 2.3% with Tecnis TIOL, and 3.3% with silicone lenses.,,, None of the cases in our study required realignment as the deviation from target axis was 6° or less. Another parameter which is associated with postoperative rotation is the axis of IOL implantation. An increased incidence of rotation has been reported in cases with vertical axis of IOL implantation (with-the-rule astigmatism), although no plausible explanation was coming forthwith in the literature search. In our study too, the extent of TIOL deviation from target axis was more in cases with WTR astigmatism as compared to ATR astigmatism (4° ± 1.41° vs. 2.62° ± 2.13°).
To date, limited literature is available comparing various powers of TIOL. Mairot et al. compared +1.0 D TIOL with +1.5 D TIOL and observed similar postoperative UDVA, SE, and residual astigmatism in both the groups. The present study compared low-power TIOLs (+1 D and +2.25 D) with medium-power TIOLs (+3.0 D, +3.75 D, 4.0 D, and 4.5 D). Our study also shows the efficacy of monofocal TIOL implantation to correct corneal astigmatism even of low degree. There is no statistical difference between low and medium TIOLs in this study for postoperative UDVA, residual refractive astigmatism, SE, and deviation from target axis. Overall, 77.4% of the eyes achieved a SE within ± 0.5 D, 75% of the eyes in Group 1 and 78.9% in Group 2. In low TIOL group, 100% of the cases achieved ≤0.75D of residual cylinder as compared to 57.9% in medium TIOL group. The limitations of this study of small sample size and consecutive sampling procedure should be acknowledged. As has been mentioned above, limited data are available in the literature comparing low- and medium-power TIOL. To our knowledge, this is only the second time that low- and medium-power TIOLs have been studied.
| Conclusions|| |
This study showed effective correction of preoperative corneal astigmatism and good visual outcomes with TIOL implantation. Despite the limitation of smaller study population, this study has brought out significant results in terms of accurate IOL alignment and good postoperative UDVA with manual marking of target axis. Further, this study observed that the power of TIOL did not influence postoperative UDVA, residual astigmatism, or deviation of TIOL from target axis. A larger controlled study is required to compare the outcomes of various powered TIOLs.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]