Biometric aspects of diffractive multifocal intraocular lenses

Area of Science:

• Ophthalmology
• Biomedical Engineering
• Optics

Background:

• Diffractive multifocal intraocular lenses (IOLs) are widely used to correct refractive errors.
• Accurate biometric calculations are crucial for achieving desired refractive outcomes with IOL implantation.
• The SRK formula series and Binkhorst formula are commonly used for IOL power calculation.

Purpose of the Study:

• To determine the A constant for diffractive multifocal intraocular lenses.
• To investigate the relationship between axial length and anterior chamber depth (ACD) in patients with multifocal IOLs.
• To provide an updated A constant for preoperative biometric calculations using the SRK-II formula.

Main Methods:

• A retrospective biometric study was conducted on 132 patients implanted with diffractive multifocal IOLs.
• Refractions for distance were performed to determine the two principal focal points induced by the IOL.
• The difference in diopters was used to calculate the A constant (SRK formula series) and ACD (Binkhorst formula).

Main Results:

• The calculated A constant was 116.46, showing consistency across various axial lengths (22mm to 24.5mm).
• For emmetropic patients with IOL power alone, the A constant was 116.3.
• The average ACD was 3.94mm, with variations observed in shorter and longer eyes.

Conclusions:

• An A constant of 116.4 is recommended for preoperative biometric calculations when using the SRK-II formula with diffractive multifocal IOLs.
• Anterior chamber depth exhibits variability based on ocular dimensions.
• These findings contribute to optimizing refractive outcomes in patients undergoing multifocal IOL surgery.