|Year : 2020 | Volume
| Issue : 1 | Page : 75-76
Toric intraocular implantation: An overview
Sandeep Gupta1, Srujana Bhaskar2
1 Associate Professor, Department of Ophthalmology, Command Hospital, Kolkata, West Bengal, India
2 Associate Professor, Department of Opthalmology, AFMC, Pune, India
|Date of Submission||16-Jun-2019|
|Date of Decision||18-Jul-2019|
|Date of Acceptance||25-Aug-2019|
|Date of Web Publication||03-Mar-2020|
Surg Cdr Srujana Bhaskar
Associate Professor, Department of Opthalmology, AFMC, Pune
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Gupta S, Bhaskar S. Toric intraocular implantation: An overview. J Mar Med Soc 2020;22:75-6
Ever-evolving advances and innovations in the field of cataract surgery have ensured improved postoperative visual outcomes and patient satisfaction. Patients are intolerant of any residual refractive errors after surgery and expect glass-free full vision. To minimize the residual refractive error postcataract surgery, especially in cases with preexisting corneal astigmatism of 1D or more, toric intraocular lenses (TIOLs) are the preferred choice of procedure. Since its introduction in 1992 as a nonfoldable polymethylmethacrylate implants to be inserted through a 5.7 mm incision, TIOLs have come a long way to the present-day foldable hydrophobic lenses which can be implanted through a 2.2 mm incision. However, it is not the one-stop solution in all patients, and few considerations are mandatory before planning these IOLs.
A good patient selection plays an essential role in obtaining optimal postoperative results after TIOLs. Higher corneal astigmatism (>4D), irregular astigmatism, and central corneal opacities are to be avoided while selecting cases for TIOL. However, with appropriate patient counseling, TIOLs could still be considered in these cases to decrease the residual astigmatism and spectacle dependence. Eyes with zonular dehiscence should not be offered TIOL as a stable capsular bag is important for intraoperative TIOL rotation for its correct alignment with the intended axis.
Precise TIOL power and axis calculation preoperatively are of paramount importance to get fairly accurate postoperative visual outcomes. To improve precision, multiple measurements are to be taken for both keratometry and axial length using IOL Master. In cases with mature cataract, dense posterior subcapsular cataract, nuclear sclerosis, and axial length could be measured with A scan. However, it is important to take axial length readings with good spikes, that the probe should be only touching gently and not pressing, and that the measured axial length should be comparable with that of the other eye. Various TIOL calculators are available online which calculate the power of TIOL and axis of its alignment using the keratometry and axial length values. Any deviation from the predicted outcomes should be thoroughly analyzed to ascertain possible fallacies and should be definitely avoided in subsequent cases.
Various marking techniques are presently in practice to mark the intended axis on the cornea before the surgery. These include the conventional manual marking methods and the recently introduced image-guided systems. Manual marking involves a three-step technique which includes placing reference marks at 3'O, 6'O, and 9'O clock position with the patient sitting/standing erect with the back resting against a wall and the gaze straight-ahead with pendulum or bubble marker; alignment of these reference marks intraoperatively with the degree gauge of the fixation ring; and finally, intraoperative marking of the target axis with the corneal meridian marker. The image-guided systems that capture the preoperative reference image subsequently perform intraoperative image registration when the limbal landmarks are used to match the two images. A graphic overlay is then displayed in the surgical field showing the target axis along which the TIOL is required to be aligned.
Although the accurate alignment of TIOL has been reported with the various image-guided systems with <5 of deviation from the intended axis,, they are expensive and hence available at only few centers. However, there is a silver lining with good visual outcomes when manual marking techniques are used with adequate meticulousness as has been shown in the ensuing study wherein the TIOL alignment has been compared with that of the image-guided systems.
Postoperative rotational stability of TIOL is another important factor in achieving optimal visual outcomes. Accurate intraoperative alignment of TIOL with the target axis, meticulous removal of viscoelastic including from behind the TIOL, and hydrophobic nature of TIOL which helps in forming strong adhesions between the IOL and lens capsule in the early postoperative period contribute toward better rotational stability in the postoperative period.
TIOL misalignment postoperatively could be caused by inaccurate calculation of the target axis of IOL alignment, inaccurate alignment of TIOL intraoperatively, and postoperative IOL rotation. There is a loss of approximately 3% of the effective cylinder power with one degree of misalignment, and the entire toric effect is lost when there is 30° of misalignment., TIOL will require realignment if there is more than 10 of rotation from the target axis as rotation <10 changes the manifest refraction by 0.5D which does not entail additional intervention.
To conclude, TIOLs are wonderful tools for giving spectacle-free vision to patients with cataract and significant astigmatism. Furthermore, manual marking techniques are as good as imaging systems if used meticulously, and once consistent results are achieved repeatedly, TIOLs can be used in patients with small amount of astigmatism also.
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