Article

No viscoelastic? Not a problem

Toric IOL misalignment is fixable without it; its absence allows IOL mobilization inside the capsular bag.

Not long ago, patients with astigmatic refractive errors required intraoperative interventions, such as astigmatic keratotomy, limbal relaxing incisions or even selective positioning of surgical incisions. But innovation has advanced the reality of near perfect vision. Today, toric IOLs provide a powerful option to correct astigmatism, ultimately leading to spectacle independence.

But correct toric IOL placement requires a little skill. As these IOLs must be placed at a specific axis, the use of a specialized, preoperative toric IOL calculator is vital. Because while rare, post-implantation rotation is a post-surgical concern.1 It is important to note that even a single degree of off-axis placement can result in compromised visual outcomes.

IOL repositioning typically occurs due to poor outcomes from primary cataract surgery. IOL misalignment, displacement and decentration resulting in poor vision or visual disturbances rank among the main reasons for reoperation.1 Furthermore, we have seen a 75% increase in secondary procedures over a 13-year period.2

Although cataract surgery has greatly developed in the past decade, physician and patient expectations of outcomes has also increased. We present a case of a patient with post-implantation toric IOL rotation that required a surgical realignment intervention to correct the residual astigmatism from the original cataract surgery.

CASE REPORT

A 79-year-old Caucasian female with no relevant past medical history was referred to our clinic for removal of her cataract in the right eye. Clinical examination showed her BCVA of 20/100 with a refraction of +2.75 sph/1.50 cyl x 169 in the right eye. Slit lamp examination revealed a combined 2+ nuclear sclerosis, 3+ posterior subscapular cataract (NO2NC2P3 as per the LOCS III grading system).

The patient wished for optimal post-operative vision without glasses, so we chose a toric IOL to reduce astigmatism. A 23.0-D AcrySof IQ Toric SN60AT (Alcon) IOL was calculated to be placed at 6 degrees with an expected target refraction of 0.01 sph/0.05 cyl x 006 using the Barrett toric calculator. Postoperatively, the patient reported blurred vision and slit lamp examination revealed the misalignment of the toric lens at 170 degrees with a manifest refraction of -1.00 sph/1.75 cyl x 060 degrees. With this much residual cylinder remaining, we decided to re-operate and rotate the IOL. We used the Toric Results Analyzer (astigmatismfix.com ) to determine the amount of IOL rotation required to decrease the residual astigmatism, with a resultant axis of 30 degrees (Figure 1). Note that the outputted axis is different from preoperative calculations, because the Toric Results Analyzer takes into account post-operative manifest refraction from the primary surgery. Not only does this refraction take into account the current lens position, it also accounts for any changes in lens tilt or induced corneal astigmatism from the surgical incisions.

Figure 1. (A) Output from the Toric Results Analyzer. IOL power and lens axis, along with manifest refraction, were inputted into the analyzer. The formula calculated that the ideal position of the IOL should be at 30 degrees, which would result in a residual refraction of -0.33 sph/0.41 cyl x 121. (B) The effect of IOL axis on the magnitude of astigmatism with the 23.0 D Acrysof IQ Toric SN60AT IOL. The lowest magnitude of astigmatism is achieved with the IOL placed at 30 degrees.

The patient returned to the operating room one month from the original surgery, and we used a “no viscoelastic” technique to rotate the IOL from 170 to 30 degrees (Figures 2 and 3). Visual acuity returned to 20/20 OD with a manifest refraction of 0.00 sph/0.50 cyl x 140 within two weeks postop, and OPD-Scan III (Nidek) confirmed the axis of the IOL at 30 degrees (Figure 4).

Figure 2. Intraoperative realignment of the 23.0 D Acrysof IQ Toric SN6AT IOL. Micrograspers (Microsurgical Technology) were used to stabilize the anterior leaflet of the capsular bag while a Sinskey lens hook (Katena) was used to dissect the IOL from the capsular bag (A-D). A Kuglen hook (Katena) was used to displace the iris while a Sinskey hook freed the IOL haptics (E/F).

Figure 3. A Kuglen hook and a Sinskey hook were used to manipulate the mobile IOL within the capsular bag (A/B) and final rotational changes were made with the Sinskey hook (C/D). The IOL was observed in the bag prior to closing (E) and after (F). The primary incision was hydrated to ensure stable placement of the IOL.

Figure 4. Two-week postoperative OPD Scan III (Nidek) of the AcrySof IQ Toric SN60AT IOL placed at 30 degrees (red line) of axis as calculated by the Toric Results Analyzer.

SURGICAL TECHNIQUE IN REALIGNMENT

Reoperation and realignment can challenge even the most skilled surgeons. The most challenging aspect of mobilizing the IOL is freeing the optic and haptics from the anterior and posterior capsular leaflets. Capsular fibrosis and contracture typically can range from two weeks to four months postoperatively.3 Once this occurs, risk of bag tear increases when manipulating the lens within the bag. In this case, OVD directed under the anterior leaflet of the capsule is used to separate the leaflets from the IOL, allowing it to be mobilized and realigned. In the setting of a toric IOL, however, this may result in retained OVD in the capsular bag with increased risk of re-rotation of the IOL.

In our case, as we re-operated shortly after initial surgery, the capsule had not fibrosed significantly, and we used a “no-viscoelastic” technique in the realignment of the IOL. As seen in Figure 2A/B, we used a set of micrograspers (Microsurgical Technology) to stabilize the anterior leaflet of the capsular bag. Then, we used a Sinskey lens hook (Katena) to help separate the surrounding anterior leaflet from the IOL (Figure 2C/D). Once freed, we introduced a Kuglen hook (Katena) and used a two-handed technique to release the haptics from the posterior and anterior leaflets (Figure 2E/F, Figure 3A/B). Once the IOL was freely moving within the bag, we used the Sinskey hook to realign the IOL to 30 degrees (Figure 3 C/D). We set the axis preoperatively using a Mastel Toric Set II (Mastel Precision INC) and confirmed lens placement postoperatively with OPD-Scan III (Nidek) and anterior segment photography (Figure 4).

TORIC MISALIGNMENT

As toric IOLs correct astigmatism, precise axis placement is crucial in optimizing post-operative visual acuity and astigmatism correction. A 1-degree off-axis rotation of the IOL has shown to result in a loss of approximately 3.3% in the lens cylinder power. Also, if the rotation is 30 degrees or more, the cylinder power is completely lost.4 One study found that the mean rotational misalignment of the AcrySof IQ Toric SN60AT IOL was approximately 4-5 degrees at two years postop.5

Furthermore, the largest rotational change of the IOL occurred within the first 24 hours with less than 1% rotating beyond 20 degrees. Those who had greater than 20 degrees of rotation had axial lengths of 25.0 mm or longer. Axial length and capsular bag size are proportionally related.6 Since the IOL is placed within the capsular bag, the larger the bag, the greater the potential for rotational instability.

Capsular bag size is one of many potential factors that can cause misalignment of a toric IOL. Intraoperative factors such as incomplete removal of OVD and insufficient extension of the IOL haptics allow for greater potential space within the capsular bag.7 Any changes due to these factors typically present in the early postoperative phase (within 24 hours) whereas capsular bag fibrosis and phimosis typically cause IOL misalignment at a later stage (around two weeks to four months).3

CONCLUSION

As IOL technology improves, the ability to achieve near perfect vision postoperatively greatly increases. Astigmatic correction is an integral part of modern cataract surgery, and toric IOLs give surgeons a powerful and reliable option in correcting astigmatism with minimal postoperative complications. Toric IOLs require precise positioning on axis, as any rotation can result in suboptimal outcomes.

Key factors in ensuring that the IOL is secured at the correct axis prior to closing the eye are confirming the haptics have fully deployed and OVD is completely removed both posterior and anterior to the IOL.

Frequent follow-ups are important to ensure proper IOL alignment — if there is a large change in alignment, the patient may require surgical intervention. An online rotation calculator (The Toric Results Analyzer) should be used to recalculate the correct axis so the least amount of postoperative astigmatism is ensured. A “no-viscoelastic” technique is a novel approach at mobilizing the IOL within the capsular bag without the need of creating potential space for movement. Ultimately, early intervention can correct these rare issues and allow the patient to achieve excellent refractive outcomes. OM

REFERENCES

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