Synchronized Real Time Imaging of Ocular Anterior Segment Biometry and Ciliary Muscle during Accommodation

Abstract

 

Purpose

 

To test the feasibility and repeatability of synchronized real-time imaging of ocular anterior segment biometry and ciliary muscle during accommodation using optical coherence tomography (OCT).

 

Methods

 

An improved OCT system using CMOS camera for scan speed improvement based on our previously reported ultra-long scan depth OCT was used (Du et al., Ophthalmology, 2012). The scan depth was 12.6 mm in air. A switchable reference arm was used to sequentially acquire a set of two frames with the placement of the zero delay lines on the top and the bottom of the anterior segment. Semi-automatic software was used to register and overlap the two frames and optical correction was performed before yielding biometric measurements. Another OCT was used to image the ciliary muscle and had a light source with the central wavelength of 1310 nm and the bandwidth of 75 nm. The two devices were combined and synchronized. The full range of the anterior segment at horizontal meridians with a frame rate of 8 fps, while the ciliary muscle at the temporal side of 7 fps, were imaged for a total time of approximately 3.7 second. The 6.00 D accommodative stimulus was given 1 second after the onset of acquisition. Four healthy subjects (age: 24.3 ± 2.1 yrs, refractive error: 4.4 ± 2.0 D) were enrolled and imaged in two separate sessions.

 

Results

 

Dynamic alternation of both the anterior segment biometry and ciliary muscle were successfully recorded and measurements matched well between two imaging sessions (Fig. 1). During accommodation, the ciliary muscle contracts as shown in the increase of the maximal ciliary muscle thickness and the forward movement of the ciliary apex. As expected, the crystalline lens became thicker and steeper in the front surface. These changes appeared to be as a function of time and the biometric alternation was almost parallel to the ciliary muscle constriction. However, hysteresis (0.5 s) of the lens reshaping (time to reach the maximal changes) compared to maximal ciliary muscle contraction occurred in two cases.

 

Conclusions

 

This pilot study demonstrated for the first time that combined OCT system is feasible to determine the dynamic alternation of the anterior segment during accommodation. The real-time relationship between anterior segment biometry and ciliary muscle contraction can be quantified reliably, which sets the stage for studying the mechanism of accommodation.

 

 

 

Keywords: 404 accommodation • 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • 456 ciliary muscle