Simultaneous real-time imaging of the ocular anterior segment including the ciliary muscle during accommodation

Bascom Palmer Eye Institute, University of Miami, Miami, FL, 33136, USA
Biomedical Optics Express (Impact Factor: 3.65). 03/2013; 4(3):466-80. DOI: 10.1364/BOE.4.000466
Source: PubMed


We demonstrated a novel approach of imaging the anterior segment including the ciliary muscle
using combined and synchronized two spectral domain optical coherence tomography devices (SD-OCT).
In one SD-OCT, a Complementary Metal-Oxide-Semiconductor Transistor (CMOS) camera and an alternating
reference arm was used to image the anterior segment from the cornea to the lens. Another SD-OCT for
imaging the ciliary muscle was equipped with a light source with a center wavelength of 1,310 nm and
a bandwidth of 75 nm. Repeated measurements were performed under relaxed and 4.00 D accommodative
stimulus states in six eyes from 6 subjects. We also imaged dynamic changes in the anterior segment
in one eye during accommodation. The biometry of the anterior segment and the ciliary muscle was
obtained. The combined system appeared to be capable to simultaneously real-time image the biometry
of the anterior segment, including the ciliary muscle, in vivo during

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    • "This is the unaccommodated state, in which the lens is kept under constant tension. Experimental support for this most commonly accepted Helmholtzian theory includes, amongst many others, an interesting paper by Shao et al. (2013) showing real-time imaging of accommodative changes in the anterior segment of the eye [2]. While experimental efforts show that lenticular spherical aberration (SA) becomes more negative with accomodation, it is clear that increasing surface curvatures cause more positive SA; thus the accommodative decrease in lenticular radii should produce more positive SA. "
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    ABSTRACT: We present an analytical method to describe the accommodative changes in the human crystalline lens. The method is based on the geometry-invariant lens model, in which the gradient-index (GRIN) iso-indicial contours are coupled to the external shape. This feature ensures that any given number of iso-indicial contours does not change with accommodation, which preserves the optical integrity of the GRIN structure. The coupling also enables us to define the GRIN structure if the radii and asphericities of the external lens surfaces are known. As an example, the accommodative changes in lenticular radii and central thickness were taken from the literature, while the asphericities of the external surfaces were derived analytically by adhering to the basic physical conditions of constant lens volume and its axial position. The resulting changes in lens geometry are consistent with experimental data, and the optical properties are in line with expected values for optical power and spherical aberration. The aim of the paper is to provide an anatomically and optically accurate lens model that is valid for 3 mm pupils and can be used as a new tool for better understanding of accommodation.
    Full-text · Article · May 2014 · Biomedical Optics Express
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    • "They have found and taken into account a latency period of around 370 ms, from a change in AS to the start of the deformation of the crystalline lens. Shao et al. (2013) recently found a latency period of 0.3 s in the response of the ciliary muscle, following a stimulus to accommodate. Campbell and Westheimer (1960) found that the amplitude of the AR to a brief pulse in AS depended on the duration of the pulse. "
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    ABSTRACT: The accommodative response (AR) to changes in dioptric accommodative stimulus (AS) during the latency period and onset of accommodation was investigated. Participants monocularly observed one period of a square wave in AS, with a 2-D baseline and mean, and amplitude 1 D or 2 D; the period of the square wave ranged from 0.10s to 1.00s; both increases and decreases were used for the first step in AS. At periods of 0.30s and longer, accommodation was found to respond to both levels of the stimulus. Rapid retinal monitoring appeared to be taking place for such stimuli. The amplitudes of peaks in AR did not usually depend on whether a particular level of AS occurred first or second, but for 8/40 conditions, a significant difference was found, with a stronger response when the level of AS occurred second. Null or incorrect responses were also observed in many trials, possibly attributable to the natural microfluctuations of accommodation. Minimum response times to the changes in AS were observed, which increased with decreasing period of the AS. The time interval between peaks in the AR decreased with decreasing period of the AS. The findings were consistent with a parallel processing model previously proposed for saccades, where input from a later change in stimulus may enter an element of the control system when that element has finished processing an earlier change. More than one change in stimulus may therefore be passing through the multi-element control system at a time.
    Full-text · Article · Aug 2013 · Vision research
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    • "In this study, we used a switchable reference arm to image the anterior segment. The galvanometer employed the reference arm, sequentially changing from one mirror to another; therefore, the zero delay line was alternatively placed on the top of the cornea and the bottom of the lens, and custom software was used to register and overlay the two images [25]. The optical correction was performed before yielding the biometric measurements, with the results shown in Fig. 9 "
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    ABSTRACT: We demonstrated the feasibility of a CMOS-based spectral domain OCT (SD-OCT) for versatile ophthalmic applications of imaging the corneal epithelium, limbus, ocular surface, contact lens, crystalline lens, retina, and full eye in vivo. The system was based on a single spectrometer and an alternating reference arm with four mirrors. A galvanometer scanner was used to switch the reference beam among the four mirrors, depending on the imaging application. An axial resolution of 7.7 μm in air, a scan depth of up to 37.7 mm in air, and a scan speed of up to 70,000 A-lines per second were achieved. The approach has the capability to provide high-resolution imaging of the corneal epithelium, contact lens, ocular surface, and tear meniscus. Using two reference mirrors, the zero delay lines were alternatively placed on the front cornea or on the back lens. The entire ocular anterior segment was imaged by registering and overlapping the two images. The full eye through the pupil was measured when the reference arm was switched among the four reference mirrors. After mounting a 60 D lens in the sample arm, this SD-OCT was used to image the retina, including the macula and optical nerve head. This system demonstrates versatility and simplicity for multi-purpose ophthalmic applications.
    Preview · Article · Jul 2013 · Biomedical Optics Express
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