Robot integrated dual-view color ophthalmic slit lamp system

Abstract

Purpose : The slit lamp is a common ophthalmic instrument for examination of the ocular anterior segment. Standard slit lamp systems require patients to be stabilized with chin and forehead rests, and therefore limit the ability to image patients who are mobility impaired. Accordingly, we developed a small form factor, lightweight robotically mounted slit lamp that illuminates the eye with a homogenous slit and accurately tracks the pupil’s location.

Methods : The custom slit projection optical system was designed in Zemax. Illumination is provided with a white light LED with a color temperature of 4900K (Thorlabs). The LED light is collimated and followed by a fly’s eye homogenizer – a pair of micro-lens arrays paired with a collecting lens - to ensure light projected onto the cornea is homogeneous. Following the homogenizer, a rectangular aperture determines the dimensions of the slit and is relayed onto the front of the eye, resulting in a working distance of 65 mm (Fig. 1A). We designed and 3D printed custom opto-mechanics (Fig. 1B) to mount the slit projection system as well as pupil tracking (FLIR) and color imaging cameras (Allied Vision) to a collaborative robot (Universal Robots, UR3e; Fig 1C).

Results : We measured the color camera resolution to be 10 lp/mm (Fig. 2AB). Utilizing monochromatic pupil tracking cameras, the system could track the pupil with 20um and 216um accuracy in the lateral and axial directions respectively. The robotically mounted slit lamp system illuminated a homogeneous slit at the cornea (Fig. 2FG). The weight of the slit lamp module was 1kg.

Conclusions : We built a robotically integrated slit lamp by using custom, 3D-printed opto-mechanics. Our system illuminated and imaged a corneal phantom with high resolution. The system also accurately tracked a pupil phantom in space.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.

 

Figure 1: A) Zemax model of the slit projection system designed to generate a rectangular slit at a working distance of 65mm. B) Fusion360 rendering of the system with custom optomechanics and cameras, mounted to a UR3e robotic arm. C) System built and mounted to a UR3e robotic arm with a polystyrene foam head at the imaging plane.

 

Figure 2: A) A USAF 1951 resolution target imaged with a color camera. B) ROI from Fig. 2A. C-E) Images captured from the three pupil tracking cameras on a pupil phantom mounted in a polystyrene foam head. F-G) Slit images captured from the color cameras on a surgical practice eye.