Prospective Comparative Study of Refractive Outcome of STAAR and Alcon Toric Intraocular Lenses
Condition: Astigamtism
Study type: Interventional

Summary: 
      Several methods have been developed to address and reduce preexisting astigmatism. The
      refractive results associated with the use of toric IOLs are likely to be more predictable.
      Other advantages of toric IOL include absence of need for any additional astigmatic
      correction procedure during cataract surgery, faster visual recovery as well as the
      reversibility of the procedure. There has not been any trial carried out to evaluate the
      results of toric IOL in either the investigators local population or in East Asia. Hence, the
      investigators set out to evaluate and compare the efficacy, safety, predictability and
      stability of the STAAR and Alcon toric IOL in Asian eyes.
    

Detailed description: 
      The improvements in surgical technique as well as advances in technology employed during
      modern cataract surgery have made it a safe procedure in routine cases. Moving forwards, the
      single most pressing challenge facing cataract surgeons in the developed countries today is
      the ability to achieve predictable and accurate refractive outcomes. Increasingly, surgeons
      and patients alike have come to measure the success of their surgery by the refractive
      outcome.

      Using partial coherence interferometry has led to more accurate biometry and consequently
      more predictable spherical results. This also helped paved the way for satisfactory
      correction of presbyopia with multifocal intraocular lenses (IOL).

      Astigmatism is also an important component of the refractive equation. Estimates of the
      incidence of significant, naturally occurring astigmatism vary widely from 7.5% to 75%1. It
      is thought that 3% to 15% of eyes may have 2 or more diopters (D) of astigmatism2. Many
      surgeons would agree that astigmatism of greater than 0.5 D will have visual consequences
      such as symptoms of ghosting and shadows and they now aim for both spherical and astigmatic
      outcomes of +/ - 0.5 D3.

      Several methods have been developed to address and reduce preexisting astigmatism. While
      corneal relaxing incisions for astigmatic correction can be unpredictable and highly surgeon
      dependent, the opposite is true for toric IOLs. The refractive results associated with the
      use of toric IOLs are likely to be more predictable as it is independent of corneal wound
      healing. The implantation of an IOL is also less surgeon dependent. Other advantages
      associated with toric IOLs include the absence of need for any additional astigmatic
      correction procedure during cataract surgery, faster visual recovery as well as the
      reversibility of the procedure.

      Studies have been carried out to evaluate the efficacy and rotational stability of the STAAR
      AA4203 TF/TL toric IOL since its FDA approval in November 1998. These trials have only been
      carried out on Caucasian eyes and have shown a significant reduction in the pre-existing
      refractive astigmatism, improvement of postoperative unaided visual acuity as well as
      excellent refractive as well as rotational stability (latter especially so with the TL
      model). Ruhswurm et al.6 reviewed 37 eyes with STAAR toric IOL over a mean duration of 20.3
      months and found that 78.4% of eyes had residual refractive astigmatism within +/- 1.00 D and
      48.6% within +/- 0.50D. 83.4% of these eyes achieved best-corrected visual acuity of 20/40 or
      better. Sun et al.7 demonstrated improved unaided visual outcome between eyes with toric (130
      eyes; 86.4% with visual acuity 20/40 or better) and spherical IOL (51 eyes; 76% with visual
      acuity 20/40 or better). Similar results have also been obtained with the Alcon toric IOL. In
      Horn et al.9, the clinical trial results of 250 patients with Alcon toric IOL have been
      described, demonstrating good unaided visual acuity of 20/25 or better at the 6-month
      postoperative visit (66% of patients with unilateral toric implant and 97% with bilateral
      implants). 97% of these toric patients achieved spectacle freedom for distance vision,
      compared to 50% of control patients. It is well documented that the rotational stability of
      these toric IOL is crucial to the efficacy of astigmatic reduction. Theoretical calculations
      show that an estimated 1/3 of astigmatic correction is lost if the IOL is rotated by 10
      degrees off axis, as well as potential worsening of preoperative astigmatism in the presence
      of more than 30 degrees of off-axis rotation. Toric IOL stability is dependent on multiple
      factors, one of which is the capsular bag size. Vass et al.11 showed a good correlation
      between axial length and capsular bag diameter (CBD), especially so in eyes with axial
      lengths of less than 25.0mm. On the other hand, highly myopic eyes are not shown to have a
      greater risk of having a larger CBD than those with normal axial lengths. A formula derived
      to calculate a predicted CBD (CBDp) showed that values greater than 10.3mm are likely to have
      existing larger CBD and hence benefit from implantation of longer toric IOL due to better
      centration.

      To date, there has not been any trial carried out to evaluate the results of toric IOL in
      either our local population or in East Asia. There has also not been any prospective clinical
      trial conducted to compare the difference (if any) between a plate-haptic and loop-haptic
      toric IOL. Hence, we set out to evaluate and compare the efficacy, safety, predictability and
      stability of the STAAR and Alcon toric IOL in Asian eyes.
    

Intervention name(s): Phacoemulsification with implantation of toric IOL
Intervention type(s): Procedure
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Single
Primary purpose: Treatment
Keywords: efficacy; safety; predictability; stability; toric IOL; refractive astigmatism; phacoemulsification