|LETTER TO THE EDITOR
|Year : 2021 | Volume
| Issue : 1 | Page : 117-119
The hidden culprit for toric intraocular lens selection - Influence of posterior corneal astigmatism in various astigmatism types
Shruthy Vaishali Ramesh1, Prasanna Venkatesh Ramesh2, Meena Kumari Ramesh1, Ramesh Rajasekaran3
1 Department of Cataract and Refractive Surgery, Mahathma Eye Hospital Private limited, Tiruchirappalli, Tamil Nadu, India
2 Department of Glaucoma and Research, Mahathma Eye Hospital Private limited, Tiruchirappalli, Tamil Nadu, India
3 Department of Paediatric Ophthalmology and Strabismus, Mahathma Eye Hospital Private limited, Tiruchirappalli, Tamil Nadu, India
|Date of Submission||12-Aug-2020|
|Date of Acceptance||30-Aug-2020|
|Date of Web Publication||27-Mar-2021|
Dr. Prasanna Venkatesh Ramesh
Mahathma Eye Hospital Private Limited, No 6, Tennur, Seshapuram, Trichy - 620 017, Tamil Nadu
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Ramesh SV, Ramesh PV, Ramesh MK, Rajasekaran R. The hidden culprit for toric intraocular lens selection - Influence of posterior corneal astigmatism in various astigmatism types. TNOA J Ophthalmic Sci Res 2021;59:117-9
|How to cite this URL:|
Ramesh SV, Ramesh PV, Ramesh MK, Rajasekaran R. The hidden culprit for toric intraocular lens selection - Influence of posterior corneal astigmatism in various astigmatism types. TNOA J Ophthalmic Sci Res [serial online] 2021 [cited 2021 May 6];59:117-9. Available from: https://www.tnoajosr.com/text.asp?2021/59/1/117/312272
Posterior corneal astigmatism has revolutionized the management of astigmatism in cataract patients with toric intraocular lenses (IOLs). Its effect has made a shifting paradigm in toric selection criteria, especially in the era where cataract surgery is considered as a refractive surgery.
We had an experience where a patient visiting for cataract surgery had a keratometric analysis with optical biometry (Lenstar) revealing corneal astigmatism of 0.48 D at 166°, for which considering the small quantity of astigmatism, monofocal, nontoric IOL (AcrySof® IQ) was advised and implanted. However, during the postoperative period, the patient had an unaided visual acuity of 20/40 and, with correction of −1.00 D cylinder at 90°, had a best-corrected visual acuity of 20/20. Considering this postoperative surprise, we did a retrospective analysis. The patient's preoperative data were entered into the online Alcon toric calculator which showed that the patient had required a SN6AT3 model to achieve emmetropia postoperatively [Figure 1]. Such a scenario would be a major setback in cases of multifocal IOL implantation.
|Figure 1: Alcon online toric calculator shows that for our patient who had against-the-rule astigmatism required a SN6AT3 model (red arrow) to achieve emmetropia postoperatively, and if a nontoric intraocular lens (red circle) was implanted, the patient would have a postoperative residual astigmatism of 0.88 D at 174°|
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Posterior corneal astigmatism varies between −0.26 D and −0.78 D. Ideally, articles suggest how it impacts the outcome for toric surgeries, but it plays a major role in selection criteria for toric IOL implantation. The majority of the cataract practitioners choose toric cases only when the magnitude of corneal astigmatic is >0.75 D., Interestingly, against-the-rule astigmatism throws a curveball at us with regards to toric outcome in terms of posterior corneal astigmatism, especially in such low magnitudes. Hence, it is essential to not just take the magnitude of astigmatism but also the type of astigmatism in your inclusion criteria for toric IOLs.
Hence, instead of reserving toric calculation for only a specific set of patients, we would suggest the utilization of online toric calculators for all patients [Figure 2] undergoing microincision cataract surgery and based on its suggestion to go ahead with IOL implantation to avoid such surprises.
|Figure 2: Alcon online toric calculator. (a) Hypothetical situation where the same magnitude of astigmatism, if present as with-the-rule astigmatism, then the calculator would suggest a nontoric intraocular lens (red arrow) for the patient to achieve emmetropia. (b) Similarly, if the patient had presented with oblique astigmatism, the calculator would suggest a SN6AT2 model intraocular lens (red arrow) to achieve emmetropia|
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]