Abstract
Purpose :
To determine how specified IOL powers should change when silicone oil substitution is combined with IOL implantation.
Methods :
Raytracing was done backwards from the retina with equiconvex 20D and 25D IOLs, of 1.5332 refractive index, to the object side of the anterior IOL surface. The 1.336 vitreous index was then replaced with 1.405 index silicone oil. Raytracing was repeated with increase in specified power (the power for 1.336 index surrounding the IOL) so that the object reduced vergence on the anterior side of the IOL matched that with the original IOL. This was done for shapes from planoconvex (X −1, front surface flat), through equiconvex (0), to planoconvex (+1, back surface flat), and for a range of axial lengths.
Results :
Fig.1 shows IOL power as a function of lens shapes between −1 and +1 and for axial lengths of 22 and 27 mm. The original IOL with vitreous is taken as an equiconvex lens of power +20D and refractive index 1.5332. Specified powers are 17.8 to 2.7D greater than the original power. For equi-convex IOLs, specified powers are 8.8 to 7.9D greater than the original power (average 8.2D). The true powers with silicone oil in the vitreous chamber are 4.5 to 2.6D greater than the original powers.
Fig.2 is similar to Fig.1, but the original IOL has power +25D. Specified values are 20.6 to 2.6D greater than those for the original power. For equi-convex IOLs, specified powers are 9.8 to 8.9D greater than the original power (average 9.4D). The true powers with silicone oil in the vitreous chamber are 4.7 to 2.6D greater than the original powers.
Specified powers are greater for 22mm than for 27mm by 1.5 to 0.6D. The effects are greater for the original 25D than for the original 20D by up to 2.9D. Effects are more pronounced as shape becomes more negative.
Conclusions :
Replacing vitreous by silicone oil increases the necessary specified IOL power. Increase varies from approximately 15% for flat back surfaces, to 40% for equi-convex lenses, and to 90% for flat front surface IOLs. True powers increase by about 16% across the range of IOL shapes. In terms of percentages, effects of changing the original IOL power and the axial length are small.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.