Intraocular lens calculations after refractive surgery.

Area of Science:

• Ophthalmology
• Refractive Surgery
• Intraocular Lens (IOL) Power Calculation

Background:

• Refractive surgery significantly alters corneal curvature, complicating standard intraocular lens (IOL) power calculations for subsequent cataract surgery.
• Accurate IOL power calculation is essential for achieving emmetropia after cataract surgery, especially in patients with a history of refractive surgery.

Purpose of the Study:

• To evaluate the impact of prior myopic refractive surgery on IOL power calculation accuracy.
• To compare various IOL calculation methods in eyes previously treated with myopic refractive surgery.
• To assess the influence of pre-operative refractive error on IOL power calculation deviations and introduce a new formula.

Main Methods:

• Retrospective case series of 21 patients undergoing cataract extraction and IOL implantation after myopic refractive surgery.
• Six IOL calculation methods were assessed: clinical history (IOL(HisK)), spectacle plane history (IOL(HisKs)), vertex (IOL(vertex)), back-calculated (IOL(BC)), average keratometry (IOL(avgK)), and flattest keratometry (IOL(flatK)).
• Methods were compared against an 'exact' IOL (IOL(exact)) for emmetropia and pre-refractive surgery manifest refraction using linear regression and paired t-tests.

Main Results:

• The IOL(HisKs) method demonstrated the highest accuracy with the smallest mean deviation from emmetropia (-0.56 +/- 1.59 D).
• IOL(BC) and IOL(vertex) showed moderate accuracy, while IOL(flatK), IOL(HisK), and IOL(avgK) resulted in significant hyperopic shifts without adjustments.
• An adjusted IOL(flatK) formula, incorporating pre-refractive surgery spherical equivalent (SEQ(m)), yielded results statistically indistinguishable from IOL(exact).

Conclusions:

• The clinical history at the spectacle plane (IOL(HisKs)) method is a reliable option for IOL power calculation in post-myopic refractive surgery eyes.
• A novel predictive formula using pre-refractive surgery SEQ(m) and current flattest keratometry provides accurate IOL power calculations.
• The IOL(HisKs) method is preferred when pre-operative keratometry readings are unavailable, a common scenario for cataract surgeons.