Optical performance of hydrophobic acrylic intraocular lenses with surface light scattering.

PURPOSE: To evaluate the potential effect of surface light scattering on the optical performance of hydrophobic acrylic intraocular lenses (IOLs) made of Acrysof material. SETTING: Alcon Laboratories, Inc., Fort Worth, Texas, USA. DESIGN: Experimental study. METHODS: Explanted IOLs from cadaver eyes with more than 50 computer-compatible tape (CCT) units of scatter were selected, yielding 7 IOLs. Clinically explanted IOLs (n = 4) were obtained after IOLs had been implanted 8.5 to 10.5 years. Explanted IOLs were matched to unused control IOLs. After proteins were removed, scatter was measured for IOLs dry, wetted (2 minutes in a balanced salt solution), and hydrated (24 hours). Badal imaging, ultraviolet-visible transmission, and modulation transfer function (MTF) measurements were performed with hydrated IOLs. RESULTS: Hydrated scatter values ranged from 80 to 221 CCT for explanted IOLs and 2 to 7 CCT for controls. No differences in Badal image resolution were observed between explanted IOLs and controls. The mean MTF values at 100 line pairs per mm (representing 20/20 visual acuity) were similar between explanted IOLs and controls. Over the range of 400 to 700 nm, a small reduction (mean 2.1% ± 1.4% [SD]) in transmission was observed. CONCLUSIONS: Surface light scattering of explanted IOLs did not affect image resolution or MTF values. Although light transmission was slightly decreased, the magnitude appeared to be inconsequential for optical performance.

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

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.

Etiology of surface light scattering on hydrophobic acrylic intraocular lenses.

PURPOSE: To study the etiology of surface light scattering on hydrophobic acrylic intraocular lenses (IOLs). SETTING: Alcon Research Laboratories, Fort Worth, Texas, USA. DESIGN: Experimental study. METHODS: Intraocular lenses were obtained from clinical explantations (n = 5), from human cadavers (n = 8), and from finished-goods inventory (controls). Surface light scattering was measured and imaged with the IOLs in various hydration states (dry, short-term wetted, and long-term hydrated) before and after proteins were quantified and removed. Selected IOL samples were analyzed with x-ray photoelectron spectroscopy, scanning electron microscopy (SEM) with energy-dispersion x-ray analysis, Fourier-transform infrared spectroscopy with attenuated total reflectance, and cryogenic SEM with a focused ion beam. RESULTS: No inorganic deposits or organic changes were observed on any IOL surface. Under clinically relevant hydrated conditions, surface light-scattering intensity was independent of proteinaceous biofilm state (P≥.11). Instead, the hydration state of the IOLs significantly contributed to the intensity of surface light scattering (P<.001); clinically explanted and cadaver-eye IOLs (but not control IOLs) exhibited minimal scatter when dry, intermediate scatter when wetted, and maximum scatter when hydrated. Subsurface nanoglistenings with diameters less than a micron and with locations up to 120 µm from the surface of the IOLs were characterized by SEM with a focused ion beam and were identified as the source of the hydration-related surface light scattering. CONCLUSION: Surface light scattering on hydrophobic IOLs was predominantly caused by hydration-related subsurface nanoglistenings within the acrylic IOL material.

Differential protein expression in lens epithelial whole-mounts and lens epithelial cell cultures.

PURPOSE: Lens fibergenesis is a problem in several types of cataract and in the posterior capsular opacification following cataract surgery. To correct improper fiber differentiation or to prevent unwanted growth on the posterior capsule following cataract surgery requires a thorough understanding of normal and abnormal fiber formation. To this end, studies were initiated to characterize fiber differentiation in the bovine lens and in lens epithelial cell cultures. METHODS: Indirect immunofluorescence and immunoblot analysis were employed to study the expression of vimentin, beta-crystallin, gamma-crystallin, filensin, aquaporin 0 and the Na, K-ATPase catalytic subunit isoforms (alpha1, alpha2, alpha3) in bovine lens epithelium whole-mounts as well as lens epithelial cell cultures propagated in medium containing 10% bovine serum or in medium supplemented with bovine serum concentrations < or =4%. RESULTS: Three distinct cell types were observed in the bovine lens epithelium. The cells of the central zone were identified by a polarized distribution of two distinct Na, K-ATPase catalytic subunit isoforms, alpha1 to the apical (fiber side) and alpha3 to the basal (aqueous humor side) membranes. Lateral to the polarized central zone, was the germinative zone of cells, best characterized by perinuclear vimentin basket-like structures and the loss of polarized Na, K-ATPase catalytic subunit isoforms. Lateral to the germinative zone were the cells of the transition zone (meridinal rows) where expression of the lens specific proteins beta-crystallin, gamma-crystallin, filensin and aquaporin 0 as well as the lens fiber-, adipocyte- and brain glia-specific Na, K-ATPase catalytic subunit, alpha2 are expressed. The cultured cells propagated in medium supplemented with 10% serum bore no resemblance to any of the cells of the bovine lens epithelium whole-mounts. The cells propagated in the medium supplemented with the lower bovine serum levels resembled the differentiating fibers of the transition zone of the bovine lens epithelium whole-mounts as well as superficial cortical fibers. CONCLUSIONS: Since the low-serum lens epithelial cell cultures bear a remarkable resemblance to early differentiating fibers, they are reasonable models for the study of early fiber differentiation or prevention of differentiation. The culture conditions employed do not yield the polarized cells of the central zone. Nor has the function of these polarized cells in lens fluid, nutrient and ion homeostasis been determined.