Anterior chamber depth measurements point to IOL formulas for best refractive outcomes

This study by Douglas D. Koch and colleagues examined the effect of anterior chamber depth (ACD) on the accuracy of 8 IOL formulas in patients with normal axial lengths (AL).  It is thought that ACD is one of the main sources of error in patients with myopic or hyperopic surprises. 

Study design

The retrospective case series included 270 patients with ALs between 22.0 mm and 25.0 mm who were scheduled for cataract surgery. The cohort was divided into 3 groups based on preoperative ACD measurements (<3.0 mm, 3.01–3.49 mm, >3.5 mm).

Outcomes

All formulas performed well in eyes within the normal range of ACD measurements.

In eyes with shallow and deep ACDs, multiple-variable vergence formulas (Barrett Universal II, Haigis, and Holladay 2) and the Olsen ray-tracing purchased version formula performed more accurately when compared with 2-variable formulas (Hoffer Q and Holladay 1) and the Olsen OLCR formula. The Barrett Universal II formula performed the best overall in these 2 groups. 

Limitations

The study is limited by its retrospective design, small sample size and inability to separate true shallow ACDs from erroneous shallowness because of thick lenses.

Clinical significance

In eyes with normal ALs, the ACD appears to be an important variable in the accuracy of IOL calculations. The findings suggest that paying close attention to preoperative ACD values and using specific formulas in these cases can improve refractive outcomes.