Abstract
Purpose :
Measurement of crystalline lens geometry in-vivo is critical to optimize performance of state-of-the-art cataract surgery. To date, in-vivo accurate estimation of crystalline lens whole shape parameters is missing. In this study we estimate lens volume (VOL), equatorial diameter (Ø) and equatorial plane position (EPP). The method was validated ex-vivo and demonstrated in-vivo.
Methods :
27 ex-vivo human lenses (19-71 y.o) were measured and whole lens 3-D volumes were constructed from custom-developed OCT images provided with distortion correction and analysis tools. In-vivo conditions were simulated for these volumes, assuming that only the information within a given pupil size (PS) was available. A parametric model was used to estimate the whole lens shape from PS-limited data. The accuracy of the estimated shape parameters was evaluated comparing estimates from the whole lens data and PS-limited data ex-vivo. Finally, the proposed models were applied to in-vivo lens measurements in 2 young accommodating (0D-6D in 1.5D steps, PS 5mm) and 2 cataract (PS 4 mm) eyes.
Results :
Crystalline lens VOL was estimated within 96 % accuracy (mean errors across lenses ranging from 8.67±6.62 to 6.88±5.98 mm3, for 4-5 mm PS). EPP was estimated with <50 µm (errors of 42±37 to 36±32 µm). Errors in Ø were 0.24±0.20 to 0.20±0.22 mm. VOL of the ex-vivo lenses increased at rates of 1.16 mm3/year, r=0.74, P<0.001; Ø increased at 8 µm/year, r=0.39, P=0.10; and relationship EPP/thickness slightly shifts forward. Lens VOL in-vivo remained almost constant with accommodation (S#1=155±1.3, S#2=180±0.7 mm3), Ø decreased at 0.03 mm/D, r=-0.95, P=0.009 and EPP shifts backward 2.5 µm/D, r=0.94, P=0.01. In the cataract eye, the estimated lens values were VOL=200.3 and 215.7 mm3, Ø=9.50 and 9.70 mm, and EPP=2.076 and 2.229 mm (distance from anterior lens) in S#1 and S#2 respectively.
Conclusions :
Quantitative OCT with dedicated image processing algorithms allows accurate estimation of whole shape human crystalline lens parameters, as demonstrated from ex-vivo measurements, where entire lens images are available. Patient-specific eye models that include the information on lens VOL and EPP are critical for better IOL selection (based on ray tracing instead of traditional regression formulas), and will help in presbyopia-correcting paradigms including crystalline lens refilling and accommodative IOLs.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.