Multicolor imaging in optic disc swelling

Abstract

Differentiating optic disc edema (ODE) from pseudo optic disc edema (PODE) continues to pose a diagnostic dilemma. Current report highlights the role of multicolor imaging (MC) in differentiating ODE from PODE. Composite multicolor images of the disc in ODE show greenish hyperreflectance that extends beyond the optic disc margins with irregular blurry margins and obscured disc vasculature whereas PODE shows a greenish hyperreflectance with clear and distinct margins and well delineated disc vasculature. MC imaging adds to the present armamentarium of imaging modalities obviating needless neurological evaluation mandatory in a case of true disc edema.

Differentiating optic disc edema (ODE) from pseudo ODE (PODE) is a diagnostic dilemma. Causes of PODE include small crowded discs, tilted discs, and optic nerve head drusen (ONHD), whereas ODE can occur secondary to raised intracranial pressure, inflammatory, ischemic, infiltrative, compressive, and traumatic optic neuropathies.[1] Herein, we describe cases of disc swelling and highlight their multicolor (MC) imaging characteristics and role in differentiating true from pseudo disc edema.

Case Reports

Case 1

A 19-year-old female presented with dimness of vision in the right eye for 5 years following blunt trauma to the eye. Her best-corrected visual acuity (BCVA) was 20/30 (−2.00 DS − 1.00 DC 90°), N6 in the right eye and 20/20, N6 (Plano) in the left eye. Color vision and pupillary reflexes were normal in both eyes. Anterior segment was normal in both eyes, and there was no evidence of inflammation. Fundoscopy of the right eye showed a choroidal rupture in the juxtafoveal region. Left eye macula was normal. The optic discs of both eyes appeared hyperemic with blurring of disc margins [Fig. 1a and b]. B-scan ultrasonography (USG) showed a hyperechoic clump over the optic nerve head (ONH) in both eyes which persisted at low gain confirming ONHD [Fig. 1c and d]. Spectral domain optical coherence tomography (SD-OCT) of the ONH showed elevation with an irregular internal optic nerve contour and hyporeflective spaces below the surface suggestive of ONHD. Composite MC image of the right and left eyes showed a hyperreflective greenish ring with discrete margins and clearly demarcated disc and retinal vasculature [Fig. 2a and e]. Infrared reflectance (IR) images of the right and left eye show clearly demarcated disc vasculature. Green reflectance (GR) and blue reflectance (BR) images of the right and left eyes showed hyperreflectivity limited to the optic disc margin [Fig. 2b-d and f-h].

Figure 1.

Fundus photograph showing disc elevation with blurring of margins and preserved vascular pattern in the right and left eye; suggestive of optic nerve head drusen (a and b). Ultrasonography B-scan showing high reflective clump echo (arrow) noted on the optic nerve head persisting in low gain in both eyes (c and d)

Figure 2.

MC, IR, GR, and BR images of the right (a-d) and left (e-h) eyes with optic nerve head drusen. MC images show a greenish hyperreflective ring with clear, discrete margins and well-delineated disc and retinal vasculature. Vasculature noted to be best seen on IR images. MC, IR, BR, and GR images of a normal individual (i-l). MC: Multicolor, IR: Infrared reflectance, GR: Green reflectance, BR: Blue reflectance

Case 2

A 63-year-old male patient, known diabetic, presented with sudden and painless diminution of vision in the right eye for the last 10 days and gradual painless diminution of vision in the left eye over the last 10 years. BCVA was 20/80;N12, 20/125;N12 in the right and left eyes respectively. The color vision score was 4 out of 21 Ishihara plates in the right eye whereas the left eye had a score of 11 out of 21. Anterior segment examination was unremarkable. Dilated fundoscopy of the right eye showed disc edema with prominence of the inferotemporal sector and splinter hemorrhages whereas that of the left eye showed temporal disc pallor [Fig. 3a]. The vessels, macula, and peripheral retina were normal in both eyes. Humphrey 24-2 visual field analysis of both eyes revealed an inferior altitudinal field defect. A diagnosis of the right eye nonarteritic anterior ischemic optic neuropathy was made. MC image of the right eye showed a greenish hue with irregular margins extending beyond the disc margins and obscuration of disc vasculature [Fig. 4a-d].

Figure 3.

Fundus photograph of the right eye in a case of nonarteritic anterior ischemic optic neuropathy showing disc edema with pronounced inferotemporal sectoral edema and splinter hemorrhages (a). Fundus photographs of the right and left eyes showing gross disc edema and disc hemorrhages with macular edema in the left eye (b and c)

Figure 4.

MC, IR, BR, and GR images of the right eye in a case of nonarteritic anterior ischemic optic neuropathy (a-d) and of the right (e-h) and left (i-l) eyes in a case of bilateral disc edema. MC images show a greenish hyperreflective ring with blurry irregular margins and obscured disc and peripapillary retinal vasculature. Image i shows extension of the greenish hue temporally involving the macula. Vasculature noted to be best seen on IR images. MC: Multicolor, IR: Infrared reflectance, GR: Green reflectance, BR: Blue reflectance

Case 3

A 38-year-old male patient, known case of diabetes mellitus (uncontrolled), presented with sudden painless diminution of vision of both eyes (OS > OD) for 1 month. BCVA was 20/25;N6, 20/125;N12 in the right and left eyes respectively. RAPD was present in the left eye. Color vision test with Ishihara plates revealed a score of 21/21 in the right eye and 1/21 in the left eye. The remainder of the anterior segment examination was normal. On dilated fundoscopy, both eyes showed gross disc edema with splinter hemorrhages [Fig. 3b and c]. Macular edema was also noted in the left eye. MRI brain done elsewhere showed diffuse mild cerebral cortical atrophy with no evidence of an intracranial space-occupying lesion. The patient was lost to follow-up thereafter. MC images of both eyes showed a diffusely greenish hyperreflectant ring with blurry irregular borders. The left eye also showed extension of this greenish hue temporally to involve the macula [Fig. 4e-l].

Discussion

MC scanning laser imaging is a recently introduced innovative technology developed for Spectralis SD-OCT (Heidelberg Engineering, Heidelberg, Germany). MC images are captured by simultaneously scanning with three individual laser wavelengths: blue (488 nm), green (515 nm), and infrared (820 nm), which penetrate tissue to different depths and therefore provide structural information from three discrete levels within the retina. The BR image provides details of the inner retina and the vitreoretinal interface. The GR image allows imaging of retinal blood vessels, hemorrhages, and exudates. The IR image visualizes structures at the level of the outer retina and choroid.[2] The ONH generally appears as a dark zone on MC images [Fig. 2i-l].

Available techniques to differentiate true and pseudo disc edema include fundus autofluorescence, fluorescein angiography, B-scan USG and SD-OCT and computed tomography.[3] MC image characteristics in papilledema have recently been reported.[4] The authors reported an elevated green ring surrounding a central shadow, blurring of disc margins, and obscuration of disc vasculature in ODE whereas lack of a ring shape, clear disc margins, well-delineated disc vasculature, and presence of a central shadow were observed in PODE.

Greenish discoloration on MC images has been observed to result from any type of thickening or elevation involving the retina. This study showcases two cases of ODE and a case of PODE (ONHD) and highlights its MC imaging characteristics.

As ODE is invariably associated with peripapillary retinal nerve fiber layer (RNFL) edema,[5] the greenish hyperreflectance tends to extend well beyond the optic disc margins resulting in irregular blurry margins [Fig. 5a and b] whereas an ONHD usually tends to have normal peripapillary RNFL thickness[5] and therefore the margins tend to be distinct and clear (with the greenish hyperreflectance being purely due to the cause of the PODE) [Fig. 5c]. In case 3 (bilateral disc edema), the greenish discoloration can be seen extending temporally due to associated peripapillary RNFL edema which was confirmed on SD-OCT [Fig. 5b].

Figure 5.

Multicolor and spectral domain optical coherence tomography peripapillary retinal nerve fiber layer images in a case of optic nerve head drusen showing well-defined, discrete margins (white arrowheads) with the absence of involvement of the peripapillary retinal nerve fiber layer (a). Multicolor and spectral domain optical coherence tomography images in cases of true disc edema showing irregular blurry margins (white arrowheads) with involvement of the peripapillary retinal nerve fiber layer (b and c). Spectral domain optical coherence tomography image (c) also shows macular edema with neurosensory detachment

Obscuration of disc and peripapillary retinal vasculature is noted in ODE while ONHD showed well-delineated vasculature. Further, the obscured vasculature was best seen on the IR images in all 3 cases [Figs. 2b, f and 4b, f, j]. The left eye in case 1 (ONHD) showed partial obscuration of superior disc vessels which we postulate may be due to irregular deposition of drusen within the ONH. Thus, in global disc edema, the intensity of the green tends to be uniform [Fig. 6a], whereas in sectoral disc edema [Fig. 6b] or PODE due to ONHD [Fig. 6c], the intensity of the green was noted to be more at the point of maximal edema or at the areas of increased deposition of drusen, respectively.

Figure 6.

Multicolor and spectral domain optical coherence tomography images of the optic nerve head. Uniform green intensity noted in global disc edema (a) while multicolor images (b and c) show increased intensity (red arrows) at points of maximal edema and elevation (white arrows), respectively

The need to distinguish between true and pseudo disc edema stems from the urgency to diagnose and manage true disc edema as these can be sight as well as life threatening plus alleviation of unnecessary costs and anxiety undertaken by patients with pseudo disc edema, not to forget the harmful effects of some of these modalities.

Further studies are definitely required to corroborate our findings, but we believe that MC imaging can act as a valuable tool in differentiating between these two entities. It can provide both morphological and functional information on the retina and the how and why of a retinal disease with a single composite image. It also has the added advantage that all required image acquisitions can be performed noninvasively with a single machine and in a nondilated pupil. MC imaging is an evolving modality. We believe our cases and further studies will provide more evidence on the validity of this exciting imaging modality.

Conclusion

MC imaging certainly is a useful tool in our arsenal of existing imaging modalities in the assessment of disc swelling, and this study attempts to highlight the same.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.