En-Face Optical Coherence Tomography: A New Method to Analyse Structural Changes of the Optic Nerve Head in Rat Glaucoma

Aim: To investigate en face optical coherence tomography ( eOCT) and its use as an effective objective technique for assessing changes in the glaucomatous rat optic nerve head ( ONH) in vivo, and compare it with confocal scanning laser ophthalmoscopy ( cSLO). Methods: 18 Dark Agouti ( DA) rats with surgically induced ocular hypertension were imaged with eOCT and cSLO at regular intervals. Assessment included three dimensional ( 3D) topographic reconstructions, intensity z- profile plots, a new method of depth analysis to define a " multilayered'' structure, and scleral canal measurements, in relation to the degree of intraocular pressure ( IOP) exposure. Results: The increased depth resolution of the eOCT compared to the cSLO was apparent in all methods of analysis, with better discrimination of tissue planes. This was validated histologically. eOCT demonstrated several significant changes in imaged rat ONH which correlated with IOP exposure, including the area of ONH ( p < 0.01), separation between retinal vessel and scleral layers ( p < 0.05), and anterior scleral canal opening expansion ( p < 0.05). Conclusion: eOCT appears to be effective in assessing rat ONH, allowing detailed structural analysis of the multilayered ONH structure. As far as the authors are aware, this is the first report of scleral canal expansion in a rat model. They suggest eOCT as a novel method for the detection of early changes in the ONH in glaucom