Engineering a Light-Attenuating Artificial Iris

Abstract

Purpose: Discomfort from light exposure leads to photophobia, glare, and poor vision in patients with congenital or trauma-induced iris damage. Commercial artificial iris lenses are static in nature to provide aesthetics without restoring the natural iris's dynamic response to light. A new photo-responsive artificial iris was therefore developed using a photochromic material with self-adaptive light transmission properties and encased in a transparent biocompatible polymer matrix.

Methods: The implantable artificial iris was designed and engineered using Photopia, a class of photo-responsive materials (termed naphthopyrans) embedded in polyethylene. Photopia was reshaped into annular disks that were spin-coated with polydimethylsiloxane (PDMS) to form our artificial iris lens of controlled thickness.

Results: Activated by UV and blue light in approximately 5 seconds with complete reversal in less than 1 minute, the artificial iris demonstrates graded attenuation of up to 40% of visible and 60% of UV light. There optical characteristics are suitable to reversibly regulate the incident light intensity. In vitro cell culture experiments showed up to 60% cell death within 10 days of exposure to Photopia, but no significant cell death observed when cultured with the artificial iris with protective encapsulation. Nuclear magnetic resonance spectroscopy confirmed these results as there was no apparent leakage of potentially toxic photochromic material from the ophthalmic device.

Conclusions: Our artificial iris lens mimics the functionality of the natural iris by attenuating light intensity entering the eye with its rapid reversible change in opacity and thus potentially providing an improved treatment option for patients with iris damage.

Figure 1

The light-responsive artificial iris was fabricated in two steps: (A) photochromic Photopia pellets were heated on a hot plate and reshaped into annular rings using a glass press and cutter, and (B) a 100-μm layer of PDMS was spin-coated on each side of the artificial iris to create a disk-shaped construct of 13-mm diameter and 350-μm thickness.

Figure 2

(A) Design schematic of artificial iris: the annular dispersion of the photochromic material, Photopia, is shown in gray. The light and dark gray represent the change in color and increased opacity of Photopia on light activation. (B) Images of the artificial iris placed on top of the University of Illinois at Chicago (UIC) logo show that visual transparency is maintained with and without activation.

Figure 3

(A) Light transmittance of the artificial iris in the ultraviolet (300–400 nm) and visible (400–700 nm) spectrum. Preactivation by exposure to 365-nm light for 30 seconds (UV activated) results in reduced transmission in the green to orange (450–650 nm) range, thus highlighting the additional light blocked by the artificial iris when outdoors or in the presence of UV light. (B) The percentage of incident light absorbed by the artificial iris increases from 12% to 60% as the intensity of the incident light on the construct is increased. Thus, the artificial iris has higher light attenuation in bright light than it does in dim light settings.

Figure 4

(A) Control. Image of glass slide with black lines. (B) Artificial iris. Image through peripheral photochromic region of artificial iris (AI): light scattering (increased thickness of blurred black lines) and decreased overall light transmission (gray background). (C) Artificial iris refocused. Image through peripheral artificial iris after focal length increased by approximately 150 μm: visual acuity restored. (D) Pixel intensity versus position along purple lines in (A) to (C). Image resolution denoted by the full width half maximum of control (A) and artificial iris refocused (C) is greater than image formed through artificial iris alone (B). Reduced light transmission (decreased baseline intensity) for images through AI (B and C) compared with control (A) was also noted.

Figure 5

Human corneal fibroblasts were cultured with either the annular Photopia disks or the complete artificial iris for up to 10 days. (A) Cell viability staining (live cells = green, dead cells = red) show similar morphology and proliferation rate between control and artificial iris–exposed HCFs, whereas cell death and detachment (black areas represent cell-free regions) was noted for HCFs cultured with Photopia. For all images, scale bar = 200 μm as seen in bottom right image. (B) Quantification of live cells elucidated that Photopia counteracts cell proliferation as live cell count did not significantly change from day 1 to 10. Control, blue; Photopia, red; artificial iris, green bars.

Figure 6

(A) ¹³C NMR spectra of Photopia and artificial iris samples immersed in PBS. The visible peaks are from mobile fractions of polymers in aqueous solution. (B) ¹³C NMR spectra of supernatant PBS exposed to Photopia and artificial iris for 1 month. The 124-ppm peak seen in Photopia supernatant is effectively blocked and not visible in the artificial iris supernatant sample. (C) Chemical structure of polyethylene, naphthopyran, and PDMS. The reversible and photoactive C-O bond in naphthopyran is indicated by a dashed line.