Implantable Collamer Lens Sizing Using Anterior Segment Optical Coherence Tomography.

To compare the actual postoperative implantable collamer lens (ICL) vault using the conventional STAAR online calculation and ordering system (OCOS), with the predicted vault of other current formulas and develop a new formula entirely based on anterior segment optical coherence tomography (ASOCT) parameters.

Magrabi hospitals & centers, Jeddah, Saudi Arabia.

Interventional case series of 275 eyes who had ICL implantation. ICL size was calculated with OCOS. Data were collected using ASOCT and corneal topography (MS39, CSO, Italy). Postoperative vaults were measured at 1 month with ASOCT. Optimal ICL sizes and predicted vault values were calculated for Nakamura 2 formula (NK2) using scleral spur to scleral spur (SS_SS) and lens rise (LR) data with different sets of coefficients (Nakamura, Mertens and our own coefficients derived from regression analysis). Multi parametric correlation analysis of available ASOCT data was performed to determine their suitability for a new formula [Eldanasoury-Pieger-Bains (EPB) formula]. Simulations were performed to compare predicted vault of different formulas. 

Analysis indicated that the NK2 formula using SS_SS and LR data did either increase the mean vault from 0.51 mm to 0.78 and 0.85 mm when using original N2 or Mertens optimized coefficients or increased the percentage of eyes with low vault when using coefficients optimized to a mean vault of 0.5 mm. Therefore, a new formula was developed using horizontal white to white, implanted ICL spherical equivalent power, pupil diameter and SS_SS data measured with the MS39. Vault predictions for this new formula were similar to actual outcomes.

The new EPB formula provided similar predicted vault results to the actual postoperative vault achieved with the original STAAR formula and could be an alternative to the OCOS.