3D Reconstruction of the Optic Nerve Head of a Phantom Eye from Images Obtained using a Slit Lamp Fitted with Low Cost Add-Ons

Abstract

Early detection and treatment are key in limiting vision loss from glaucoma, the second leading cause of blindness worldwide. Morphological alteration of the optic nerve head (ONH), detectable early in the condition, is a key clinical indicator. The mainstay for evaluation in clinics is the subjective assessment of stereoscopic ONH images. If quantitative diagnostic devices, which extract 3D information and use this to make an objective assessment, could be made affordable, it could mean greater diagnostic capability in primary/community care. A potentially cost-effective solution is to extract, using computer stereo vision, 3D information from stereo images obtained through a slit lamp, a mainstay of eye diagnostics, present in practically all ophthalmology and optometry practices. This work shows 3D ONH reconstruction in an eye phantom through a common slit lamp fitted with low cost cameras. Quantitative reconstructions, in close agreement with ground truths, were obtained.

Low-Cost Eye Phantom for Stereophotogrammetry-Based Optic Nerve Head Topographical 3D Imaging

“…These were machined from Terracotta using a CNC engraving machine (Shenzhen Ni Xing Ni Shang Electronic Commerce Co Ltd, Shenzhen, China) with a 10º, 0.1 mm diameter engraving bit (Man Hing Steel Iron Engineering Company, Hong Kong, China). The shape of the ONH models was generated in the same manner as in our previous work [7] but had a different scale, as appropriate for this life-sized eye phantom. The ONH models, on the mounts, are depicted in Fig.…”

“…The stereophotogrammetry-based topographical optic nerve head (ONH) imaging system from our previous work [7], consisting of a slit lamp modified to deliver binocular images to an appropriate processing algorithm, was used to capture stereo image pairs of the normal and glaucomatous ONH models of the fabricated eye phantom. Here, we marginally updated the processing algorithm to divide the region of interest into 20 x 20 blocks instead of 15 x 15 which we estimate are necessary in order to cover the optic nerve head area with a number of points more appropriate for future clinical work.…”

“…It was designed specifically for use with stereophotogrammetry-based ONH topographical imaging systems, however it is possible to modify the design for use in other areas. We demonstrate also the imaging of the phantom with an upgraded version of the stereophotogrammetry-based ONH topographical imaging system described in our previous work [7].…”

“…Where specialists cannot be present, quantitative imaging technologies that can provide an objective assessment of the ONH, such as optical coherence tomography (OCT) and the Heidelberg Retinal Tomograph (HRT), could be advantageous [6] but their high cost is prohibitive in most middle-and low-income settings and, even in high-income settings (such as community based optometry), only marginally suitable for mass population screening. Quantitative ONH imaging systems based on stereophotogrammetry, such as we described in previous work [7], could potentially be a cost-effective alternative.…”

“…In the development of such systems, eye phantoms play a crucial role in calibration and performance evaluation. Eye phantoms have previously been reported by researchers working in this area [7], [8]. In both cases, the eye phantoms were very simplistic: they contained a single lens for refractive power, were air-filled and were not true to scale, thus incorrectly mimicking artefacts and aberration, hence of dubious validity for testing imaging devices designed for human eyes.…”