True retinal topography: quantitative curvature maps of the retina using OCT

Abstract

Purpose : Retina deformations such as staphylomas in myopia or scleral flattening in high intracranial pressure can be difficult to detect on en face imaging. On the other side of the eye, corneal topography has allowed for earlier detection and quantitative longitudinal tracking of corneal deformation. In a similar fashion, retinal topography could be used for diagnosis of retinal deformations. Accurate 3D spatial measurements of the posterior segment from OCT are difficult due to optical distortions. Using a custom whole eye OCT system, we describe the generation of true retinal topography maps in normal and pathologic eyes.

Methods : We developed a custom whole eye SS-OCT system (λ0=1045nm; 100 kHz) that simultaneously imaged both the anterior and posterior eye in a single volume. Information from the anterior eye was used to correct distortions to the retinal OCT volume for each subject. The segmented and corrected retinal pigment epithelium was used to generate a spatially accurate 3D elevation map. From the elevation map, we generated a meridional curvature map following the conventions of corneal topography where r – radial position, M – elevation, and K – curvature: K(r) = δ²M(r)/δr²*(1+(δM(r)/δr)²)^-3/2. Three subjects: one normal, one with papilledema due to elevated intracranial pressure, and one with pathologic myopia (N = 6 eyes) seen at the Duke Eye Center were imaged with whole eye OCT under an IRB approved protocol.

Results : The normal subject exhibited uniform curvature over the majority of the RPE (Fig. 1 A, OD). In the subject with elevated ICP (Fig. 1 B, OD), localized flattening at the nerve head can be seen in the nasal region of the image. In the pathologic myopia subject (Fig. 1 C, OS), two features stand out: 1) steep curvature can be seen due to a staphyloma in the superior-temporal region and 2) a convex surface can be seen in the nasal region, where the retina is locally bowing inward.

Conclusions : OCT based retinal topography could help clinicians more readily recognize posterior eye deformations. By correcting for optical distortions using whole eye OCT, we can create spatially accurate topographies that allow for detection of subtle changes over time or across a population.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

Retinal topography maps covering 1cm diameter centered on the fovea for three subjects. Color map uses the following to describe local curvature: yellow - pathologically steep, green - normal, blue/purple - flat, red - convex.