Study ID
Intervention
Comparison group
Follow-up
Preoperative astigmatism
Study population
Freitas et al. 2014
Toric IOL in both eyes (AcrySof Toric TM, Alcon, Fort Worth, TX)
Non-toric IOL (AcrySof Natural, Alcon) + limbal-relaxing incisions in both eyes
1 + 3 + 6 months
O.75–2.5 D (both eyes)
Toric: 15 patients (30 eyes); age 65.7 years Non-toric: 16 patients (32 eyes); age 71.8 years
Gangwani et al. 2014
Multifocal toric IOL (Mflex-T multifocal toric IOL, Rayner IOLs, East sussex, UK) in 1 eye of a patient
Non-toric multifocal IOL (M-flex, Rayner IOLs) in the other eye + peripheral corneal-relaxing incisions
3 months
1.0–2.5 D
29 eyes in both groups; age 74.8 years (4.6)
Himschall et al. 2014
Rayner T-flex toric IOL (Rayner) in 1 eye
C-flex or Superflex non-toric IOL (Rayner) + 1 or 2 relaxing peripheral corneal incisions in the other eye
1 + 6 months
1.0–2.5 D
60 eyes (30 patients); age 71.0 years (8.4)
Holland et al. 2010
AcrySof Toric (SA60T3-T5, Alcon)
Non-toric IOL (AcrySof SA60AT, Alcon)
1 year
≥0.75 D with-the-rule astigmatism or ≥1.0 D against-the-rule astigmatism
Age: 71 years Toric: 241 eyes non-toric:236 eyes
Lam et al. 2015
TECNIS Toric IOL (Abbott Medical Optics (Santa Ana CA)
TECNIS 1-piece IOL with limb-relaxing incision
1 + 3 months
≤3.0 D
Age: Non-toric: 67.7 years (6.9), toric: 64.8 (10.3) Toric: 31 eyes of 31 patients
Liu et al. 2014
Toric IOL (model and manufacturer not specified)
Non-toric IOL (model and manufacturer not specified) + peripheral corneal-relaxing incisions
1 + 6 months
Group A: 0.75–1.5 D group B: 1.75–2.5 D
Age: Non-toric: 70.5 years (8.0), toric: 67.3 years (10.3) Toric: 15 patients in group A and 12 in group B
Maedel et al. 2014
Aspheric toric IOL (Lentis Unico L-312 T, Oculentis GmbH, Berlin Germany)
Aspheric non-toric IOL (Lentis Unico L-312, Oculentis GmbH) + opposite clear corneal incisions
1 h, 1 week, 3 + 9 months
1.04–2.11 D (mean 1.69, SD 0.41)
Age: 70.1 (11.8) Toric: 18 eyes non-Toric: 21 eyes
Mendicute et al. 2009
Toric IOL (AcrySof Toric SN60T3, SN60T4, SN60T5, Alcon)
Non-toric IOL (AcrySof SN60AT, Alcon) + opposite clear corneal incisions
3 months
1–3 D
Toric: 20 eyes; age 69.3 years (8.2) non-toric: 20 eyes; age 71.9 (6.8)
Mingo-Botin et al. 2010
Toric IOL (AcrySof Toric, Alcon)
Non-toric IOL (Acrysof natural, Alcon) + peripheral corneal-relaxing incisions
3 months
1–3 D
Toric: 20 eyes; age 71.5 years (11.1) non-toric: 20 eyes; age 75.6 (5.9)
Titiyal et al. 2014
Toric IOL (AcrySof IQ Toric, Alcon)
Non-toric IOL (AcrySof IQ, Alcon) + astigmatic keratotomy
1 day, 1 week, 1 + 3 months
1.25–1.3 D
Toric: 17 eyes; age 60.7 years (5.99) non-toric: 17 eyes; age 62.23 years (3.29)
Visser et al. 2014
Toric IOL (AcrySof aspheric toric, SN6AT3-T9, Alcon)
Non-toric IOL (AcrySof aspheric non-toric, Alcon, SN60WF)
1 week, 1 + 3 + 6 months
≥1.25 D
Age: 74 years Toric 41 patients (82 eyes) non-toric: 45 patients (90 eyes)
Waltz et al. 2015
Toric IOL (TECHNIS toric ZTC150, Abbott medical optics
Non-toric IOL (TECHNIS 1-piece ZCB00 IOL, Abbott medical optics)
1 day, 1 week, 1 + 3 + 6 months
0.75–1.5 D
Toric:102 patients; age 71.3 years (9.1)non-toric:95 patients; age 69.9 years (7.6)
Zhang et al. 2011
Toric IOL (TECHNIS toric ZTC150, Abbott medical optics)
Non- toric (AcrySof non-toric SN60AT, Alcon)
1 + 3 + 6
≥ 0.5 to ≤3 in both eyes
Toric: 30 patients (60 eyes); age 67 years (10) non-toric: 30 patients (60 eyes); age 65 years (12)
]. As many as 10% of these lenses rotated from the axis of initial placement, as assessed by objective measures using photographic retro-illumination techniques. Although the late rotation was seldom a problem, especially with larger fenestration modified haptics, the issue remained due to unacceptably high rates of repositioning required. Subsequent development of tIOLs based on a single piece and three-piece acrylic platforms resulted in better lens stability. The impact of lens material was found to be a major factor (Table 5.1). Silicone and PMMA lenses are much less adherent to the capsule than acrylic lenses.
Rotation of the lens by 15° from ideal axis can reduce the clinical effectiveness by 50%. For tIOL positions that are 30° from ideal placement, the entire corrective effect is negated, and beyond this there will be increasing residual astigmatism. Optically, the axis of residual astigmatism is found to be 45° from the midpoint of intended ideal lens position and the actual position.
Optically the effect of off-axis placement of a lens is described by
Tilt and decentration of the tIOL can degrade the optical quality of the outcome as well. Thus, in cases where IOL stability in the bag cannot be ensured, alternative fixation must be considered. Options include optic capture in the capsulorrhexis, iris fixation, or scleral fixation. However, these techniques are not as amenable to precise axis placement as primary in-the-bag fixation of the tIOL. As such, secondary means of correction may be needed and the patient counseled accordingly.
Intentional residual astigmatic refractive error can improve the depth of focus, but more than 0.75 diopters, or even less at an oblique meridian, will compromise the image quality such as to nullify the benefit. Ideally the conoid of Sturm would straddle the fovea. Alternatively, a simple myopic astigmatic result, with one focal blur circle of the conoid on the fovea and one anterior to it, would give a measure of pseudo-accommodation.
5.2 Operative Considerations
Surgically induced astigmatism (SIA) can be a significant consideration in the choice of tIOL power and axis of placement. It has been shown to be more important in lower magnitude astigmatism correction and with temporal cataract incision placement. Even with small incision and micro-incisional techniques, the SIA cannot be considered to be nil; however, it may have less and less impact on the target of axis of tIOL placement. Calculation of SIA, and lens constant optimization can be concurrently achieved with a limited data set and using widely available tools. Once a surgeon’s estimated SIA is known, and the incision location is identified, the information is entered into toric IOL calculator software. Some of this is available online. Desktop computer software allows surgeons to retain an ongoing data set for refinements in biometric calculations and SIA.
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