The mechanisms of vision loss associated with a cotton wool spot

Abstract

We characterized the perceptual, functional, and structural abnormalities associated with retinal ischemia during a cotton wool spot episode and its sequelae. The border of the visually salient field anomaly mirrored the quantitatively measured relative scotoma. Results of resolution perimetry and high resolution imaging indicated that there was a substantial loss of retinal ganglion cells within the affected region. A disruption in retinal nerve fiber arrangement was found at the cotton wool spot and within the arcuate relative scotoma. The presence of the arcuate relative scotoma is consistent with the hypothesis of failed signal transmission along the axons that pass through the cotton wool spot. The different levels of loss associated with the arcuate and focal scotomas indicate different underlying pathologies.

Figure 1

(a). Fundus photographs from 27-Sept-04 revealed a cotton wool spot (arrow) located at 10° from the fovea in the superior nasal retinal. The optic nerve appears normal. (b) Fluorescein angiography (27-Sept-04) revealed focal hypofluorescence in the region of the cotton wool spot. (c) fundus photographs one month after the images in (a) showing a reduced cotton wool spot. The line superimposed on the image shows the location of a StratusOCT scan. (d) StratusOCT image showing hyper-reflective tissue at the site of the lesion (arrow). (RNFL = retinal nerve fiber layer; ONL = outer nuclear layer; RPE = retinal pigment epithelium). (e) Fundus photograph 8 months after the initial event.

Figure 2

Target locations for resolution perimetry. Resolution acuity was measured at 7 different retinal areas of the right eye. Areas L1, L2, and L3 are inside the lesion. Shaded area indicates the region of the relative scotoma mapped by low-contrast computer-based kinetic perimetry.

Figure 3

Overlay of a subjective map of the visual anomaly (19-Sept-04) onto a fundus photograph taken 27-Sept-04. Fundus photograph (30 degree field) was inverted and scaled to match the visual field drawing retaining coincidence of the fixation point and blind spot in the field map with the foveal center and optic nerve head in the fundus image.

Figure 4

The border of the arcuate relative scotoma obtained by low contrast computer based kinetic perimetry as observed 7-Oct-04 (filled triangles, solid lines) and on 3-Dec-04 (filled circles, dashed lines). The small focal absolute scotoma, observed with high contrast perimetry as observed on 3-Dec-04 (black polygon) and on 16-Oct-08 (gray ellipse). Two small areas of vision were observed within the focal scotoma (white circles) when measured on 16-Oct-08.

Figure 5

High resolution AOSLO images of cone photoreceptors and RNFL on the CWS and the corresponding healthy retinal region on the same eye. (a) Fundus photograph of the affected eye indicating sampled regions. Region 1 is a corresponding control region of healthy retina. Region 2 is the location of CWS. Montages of RNFL at the control region (b) and the CWS (c) subtend approximately 2.5° horizontally. Scale bars represent 250 microns. Magnified views of cone photoreceptors and RNFL as indicated by the white boxes on (b) & (c) are shown in (d) – (g).

Figure 6

On Sept-08, infrared image in the affected eye (a) reveals a RNFL bundle defect (arrows) starting from the resolved CWS and ending closely to the horizontal raphe of the retina. Infrared image on the fellow eye (b) shows no such abnormality.

Figure 7

(a) Infrared image of the affected eye (OD), white arrow indicates the location of the resolved CWS. The SDOCT scan across the retina as indicated by the vertical line is shown in (b). The SDOCT scan across the retina indicated by the white section of the vertical line is shown in (c). (c), (d), and (f) show matching images from the fellow eye. (RNFL = retinal nerve fiber layer; GCL = ganglion cell layer; ONL = outer nuclear layer; OS/IS = junction of outer segment and outer segment of photoreceptors)

Figure 8

(a) Infrared image of the affected eye (OD), white arrow indicates the location of the arcuate lesion. The SDOCT scan across the retina as indicated by the white vertical line is shown in (b). (c) and (d) show matching images from the fellow eye.