Impact of Posterior Corneal Surface on Toric Intraocular Lens (IOL) Calculation

Area of Science:

• Ophthalmology
• Corneal Biomechanics
• Refractive Surgery

Background:

• Toric intraocular lens (IOL) calculations are crucial for correcting astigmatism during cataract surgery.
• Accurate prediction of total corneal astigmatism is essential for optimal visual outcomes.
• The contribution of the posterior corneal surface to total astigmatism is increasingly recognized.

Purpose of the Study:

• To quantify the impact of posterior corneal astigmatism on the accuracy of toric IOL calculations.
• To compare anterior-only corneal astigmatism measurements with total corneal astigmatism (anterior + posterior).
• To evaluate the clinical significance of posterior cornea measurements in toric IOL power selection.

Main Methods:

• Retrospective analysis of 379 eyes undergoing cataract surgery with non-toric IOL implantation.
• Corneal astigmatism measured using Placido-topography (TMS-5) and Scheimpflug imaging (IOLMaster, Lenstar).
• Comparison of anterior, posterior, and total corneal astigmatism with postoperative refractive astigmatism using vector analysis.

Main Results:

• The average absolute vector difference between anterior and total corneal astigmatism was minimal (0.3 ± 0.2 D).
• Total corneal astigmatism measurements showed a smaller deviation from refractive astigmatism compared to anterior measurements alone.
• Posterior cornea consideration slightly reduced with-the-rule (WTR) astigmatism and increased against-the-rule (ATR) astigmatism.

Conclusions:

• Posterior corneal measurements have a small but statistically significant impact on toric IOL calculation accuracy.
• Incorporating posterior cornea data can refine toric IOL selection.
• Measurement of the posterior cornea is recommended to identify atypical cases, such as early keratoconus, potentially missed by anterior surface analysis.