Sapphire ball lensed fiber probe for common-path optical coherence tomography in ocular imaging and sensing

Abstract

We describe a novel common-path optical coherence tomography (CP-OCT) fiber probe design using a sapphire ball lens for cross-sectional imaging and sensing in retina vitrectomy surgery. Single mode Gaussian beam (TEM⁰⁰) simulation was used to optimize lateral resolution and working distance (WD) of the common-path probe. A theoretical sensitivity model for CP-OCT was prosed to assess its optimal performance based an unbalanced photodetector configuration. Two probe designs with working distances (WD) 415μm and 1221μm and lateral resolution 11μm and 18μm, respectively were implemented with sensitivity up to 88dB. The designs are also fully compatible with conventional Michelson interferometer based OCT configurations. The reference plane of the probe, located at the distal beam exit interface of the single mode fiber (SMF), was encased within a 25-gauge hypodermic needle by the sapphire ball lens facilitates its applications in bloody and harsh environments. The performances of the fiber probe with 11μm of lateral resolution and 19μm of axial resolution were demonstrated by cross-sectional imaging of a cow cornea and retina in vitro with a 1310nm swept source OCT system. This probe was also attached to a piezoelectric motor for active compensation of physiological tremor for handheld retinal surgical tools.

Keywords: fiber probe; optical coherence tomography; retina imaging.

Fig. 1

(Color online) Schematic of CP-swept source optical coherence tomography (SSOCT) compatible with a dual-arm configuration. A. CP-SSOCT with a lensed probe. The fiber tip functions as a reference plane, and there is an air gap or UV epoxy between the fiber tip and ball lens as spacer. B. Goal of lensed probe is for forward viewing in retina vitrectomy surgery, and the probe is attached to the minute surgical forceps.

Fig. 2

Theoretical sensitivity and experimental results. A, Sensitivity of CP-OCT is in black with backward optical coupling efficiency of 40%; experimental results are in green; CP-OCT with backward coupling efficiency of 86.5% (1/e² width) is in cyan; traditional balanced SSOCT with backward coupling efficiency of 86.5% is in blue. B, SNR and falling off of two probes. The probe with a focal length of 415μm is shown in green and 1221μm in black. The SNR and plots were directly obtained from purely single A-scan without any A-scan average.

Fig. 3

Cow’s cornea and retina images (H 2.75 mm by V 2.1 mm) A, Cornea image. We can clearly identify the following five layers: epithelium (1), Bowman’s layer (2), stroma (3), Descemet’s membrane, (4), and endothelium (5). B, Corneal image far away from the apex. C is the OCT cross-sectional image of optical nerve head. D is away from the optical nerve head and shows clear layer structures of retina. E and F were captured when the probe was immersed in vitreous gel with a length of 32 mm. All images in Fig. 3 did not have frame average.

Fig. 4

A: Distance between the lensed fiber probe tip and the phantom surface. At 2.0mm, the compensation PZT motor is off and OCT signal shows a strong oscillation introduced on purpose. The other segments are with compensation on so that the probe follows the movement.