Measuring ultraviolet-visible light transmission of intraocular lenses: double-beam mode versus integrating-sphere mode

Abstract

This study compared integrating-sphere and double-beam methodologies for measuring the ultraviolet/visible transmission of intraocular lenses (IOLs). Transmission spectra of control IOLs and clinically explanted IOLs were measured with an optical spectrophotometer in two optical configurations: single-beam mode with integrating sphere detector and double-beam mode with photodiode detector. Effects of temperature and surface light scattering on transmittance were measured. Effects of lens power were measured and were modeled with ray-tracing software. Results indicated that transmission was consistent over a range of IOL powers when measured with the integrating-sphere configuration, but transmission gradually decreased with increasing IOL power (in a wavelength-dependent fashion) when measured with the double-beam configuration. Ray tracing indicated that the power-dependent loss in transmission was partially due to higher-powered IOLs spreading the light beam outside of the detector area. IOLs with surface light scattering had transmission spectra that differed between double-beam and integrating-sphere configurations in a power-dependent fashion. Temperature (ambient or physiological 35°C) did not affect transmission in the integrating-sphere configuration. Overall, results indicated that double-beam spectrophotometers may be useful for measuring transmittance of low-power IOLs, but an integrating-sphere configuration should be used to obtain accurate measurements of transmittance of higher-power IOLs.

Determination of scattering in intraocular lenses by spectrophotometric measurements

“…The most common are usually around 21 diopters (D), but they can range from 10 to 30 D. This makes no difference in the case of measures performed with an integrating sphere, since in spite of the beam of light refracted by the IOL opening to a greater or lesser degree, all the radiation penetrates into the sphere and, therefore, the measurement does not depend on the power of the lens. On the other hand, as Akinay et al 13 previously reported, the effect of the IOL power can prove to be considerable in the case of DB measurements. As Fig.…”

“…All the measurements were performed at room temperature as it has already been demonstrated 13 that there is no significant variation in the result of the measurements when they are performed at room temperature 35°C. The PerkinElmer Lambda 35 spectrophotometer is accurate within AE1% transmittance, so any difference greater than 1% could be optically considered significant.…”

“…As mentioned above, Akinay et al 13 previously reported the differences between measuring the spectral transmission of intraocular lenses with an integrating sphere (SB mode) and directly (DB mode): they recommended using the integrating sphere in general and only using the DB mode in the case of low power IOLs. In fact, the integrating sphere mode [14][15][16] is always used for ascertaining not only the shape of the spectral transmission curve, but also the total amount of light that passes through the IOL.…”

“…This would obviously produce an artefact when measuring scattering as the difference between the measurement with an integrating sphere and a direct DB measurement would not be exclusively due to scattering but rather that there could be losses caused by the high powers. A way of solving this problem, as Akinay et al 13 pointed out, is by changing the distance between the IOL and the spectrophotometer condenser lens that focuses the light in its photodetector. As Fig.…”

“…The difference between both measurements quantitatively shows the light lost due to scattering. In the case of direct light (DB), however, it would be necessary to study and minimize the influence that the IOL power can bring about on the measurements because Akinay et al, 13 when comparing the spectral transmission measurement of the IOLs with an integrating sphere and direct light (SB), reported the effect that the IOL power has on the direct measurement. Another advantage of this method is that when the complete spectrum is obtained of both the visible and the ultraviolet A and B, we can determine which wavelengths are the most scattered in the different cases.…”