**2. A short history and clinical outcomes of toric IOLs**

The first article reporting a toric IOL (Nidek NT -98B) was published in 1994 [9], which had a cylinder power of 2.00 or 3.00 D. In the study, Shimizu et al. had relatively positive results, although some negative results still occurred in some eyes of which the lens axis rotated more than 30° [9]. Ever since then, with the predictability increasing and the safety enhancing, toric IOLs have definitely become a considerable option to correct significant astigmatism when undergoing cataract surgery [10, 11]. At present, standard toric IOLs are available in cylinder powers of 1.0 to 6.0 D, while higher cylinder powers are also available (see **Table 1**).

Toric IOL had achieved increasingly great visual outcomes. An uncorrected distance visual acuity (UDVA) of 20/40 or better is achieved in more than 70% of


better and 41.4% had a UDVA of 20/25 or better [9]. Similar results were found in

From a social cost-effectiveness perspective, toric IOLs were inferior to monofocal IOLs in a recent prospective study [34], which should be noted in health-

Compared with incisional astigmatic keratotomy, toric IOLs offered better predictability and stability of correction [17], especially in moderate to high astigmatism [30]. In a recent meta-analysis (including 13 RCTs with 707 eyes), toric IOLs provided better distance visual acuity and lower amounts of residual astigmatism, combined with greater spectacle independence, than nontoric IOLs even when

For a toric IOL, the keratometric astigmatism (both axis and magnitude) of the

Traditionally, keratometry and topography take into account only the anterior corneal curvature [35]. However, nomograms predict total corneal astigmatism based on the power and axis of the anterior corneal astigmatism, assuming a fixed ratio between the anterior and posterior curvature [36]. These methods obviously cannot take outliers and irregularities into account (e.g., post-refractive surgery eyes) [35], thus leading to significant postoperative and/or overcorrection. However, if the agreement of measurement of astigmatism between instruments of different kinds is poor (more than 10°), the selection of toric IOLs requires extra care.

The astigmatism of posterior cornea is generally minus lens of against-the-rule. As mentioned above, ignoring effects of actual posterior corneal curvature may lead to inaccuracies in total astigmatism estimation in some eyes. In a recent study [36], for those eyes who received IOLs with 2 diopters of cylinder or less, a coefficient of adjustment of 0.75 for with-the-rule astigmatism and 1.41 for against-the-rule astigmatism can be applied to the corneal astigmatism power value to calculate a more appropriate IOL cylinder power than that be calculated by using unadjusted

Since minimizing the residual refractive error is especially critical in toric multifocal IOLs [37], imaging systems that measure posterior corneal curvature, as well as the new algorithm that incorporates the effect of posterior corneal astigmatism, are increasingly being invented. For example, the Scheimpflug imaging systems, slit scanning systems, and OCT systems could measure posterior corneal curvature, besides the anterior curvature. In a comparative study [35] including a Scheimpflug tomography (OCULUS Pentacam), a Placido topographer (Tomey TMS-5 in Placido mode), a swept source/Fourier domain OCT (CASIA SS-1000), an autokeratometer (Haag-Streit Lenstar), and a hybrid topographer (Tomey TMS-5), the OCULUS Pentacam has the disadvantage of high measuring noise on posterior corneal curvature. Meanwhile, the highest precision for planning toric IOL power and axis was achieved by combining the keratometry and OCT data. In a recent study, Lu et al. found that a novel multicolored spot reflection topographer system

another high-quality RCT [29].

*DOI: http://dx.doi.org/10.5772/intechopen.90153*

*Toric Intraocular Lenses*

relaxing incisions were used [33].

**3. The measurement of astigmatism**

cornea must be accurately measured.

**3.1 Anterior corneal curvature**

**3.2 Posterior corneal curvature**

anterior corneal curvature measurements.

**37**

care decision-making.

#### **Table 1.**

*Summary of commercially available toric IOLs.*

the cases, and spectacle independence has been reported in more than 60% of the patients in previous studies [12, 13, 15–23, 25–30], which is significantly increased compared with nontoric monofocal IOLs [31, 32]. A randomized controlled trial (RCT) compared the outcomes of AcrySof toric IOLs with conventional spherical IOLs and observed a UDVA of 20/40 or better in 92.2% of cases undergoing toric IOL implantation, with 63.4% having a UDVA of 20/25 or better. In contrast, only 81.4% of cases undergoing nontoric IOL implantation had a UDVA of 20/40 or

*Toric Intraocular Lenses DOI: http://dx.doi.org/10.5772/intechopen.90153*

better and 41.4% had a UDVA of 20/25 or better [9]. Similar results were found in another high-quality RCT [29].

Compared with incisional astigmatic keratotomy, toric IOLs offered better predictability and stability of correction [17], especially in moderate to high astigmatism [30]. In a recent meta-analysis (including 13 RCTs with 707 eyes), toric IOLs provided better distance visual acuity and lower amounts of residual astigmatism, combined with greater spectacle independence, than nontoric IOLs even when relaxing incisions were used [33].

From a social cost-effectiveness perspective, toric IOLs were inferior to monofocal IOLs in a recent prospective study [34], which should be noted in healthcare decision-making.
