The Ebola virus may leave a retinal scar specific to the disease, according to researchers.“The distribution of these retinal scars or lesions provides the first observational evidence that the virus enters the eye via the optic nerve to reach the retina in a similar way to West Nile virus,” said Dr Paul Steptoe of the Royal Liverpool Hospital, in a press release.
The Ebola virus may leave a retinal scar specific to the disease, according to researchers.
“The distribution of these retinal scars or lesions provides the first observational evidence that the virus enters the eye via the optic nerve to reach the retina in a similar way to West Nile virus,” said Dr Paul Steptoe of the Royal Liverpool Hospital, in a press release.
Dr Steptoe and colleagues presented the finding in the journal Emerging Infectious Diseases. They found a novel retinal lesion following the anatomic distribution of the optic nerve axons in 14.6% of Ebola survivors and no controls, suggesting neuronal transmission as a route of ocular entry.
“Luckily, they appear to spare the central part of the eye, so vision is preserved,” Dr Steptoe said in the press release.
He added: “Our study also provides preliminary evidence that, in survivors with cataracts causing reduced vision but without evident active eye inflammation (uveitis), aqueous fluid analysis does not contain Ebola virus, therefore enabling access to cataract surgery for survivors.”
Estimates of the incidence of ocular symptoms among survivors of Ebola range from 14% to 60%. Reports of evidence of acute uveitis from ophthalmic examination range from 18% to 58%.
Uveitis classification has also varied, with 36% to 62% reported as anterior, 3% intermediate, 26% to 36% posterior and 18% to 25% panuveitis.
Little is known regarding the medium- to long-term visual outcome of survivors or the rates of background uveitis and chorioretinal lesions within the local population.
The researchers used an ultra-widefield retinal camera to examine 82 Ebola survivors from the Ebola Treatment Unit at the 34th Regiment Military Hospital in Freetown, Sierra Leone, who had previously reported ocular symptoms, and 105 unaffected controls from civilian and military personnel.
Lesion shape varied among post-Ebola eyes, but they all shared an angular shape-often resembling a diamond or wedge-that is uncharacteristic of any other retinal disease, the researchers reported. They hypothesised that the sharp appearance of these lesions may be due to the tight triangular packing of the retinal cone mosaic.
Optical coherence tomography (OCT) revealed that the lesions were limited to the retina and located either adjacent to the optic disc or in the fundus periphery. Despite the proximity to the optic nerve head in eight cases, the area showed no swelling or pallor.
The team observed curvilinear projections from the disc margin that appear to align with the anatomic pathway of the retinal ganglion cell axons that constitute the optic nerve around the lesions near the optic nerve head.
From this distribution, they speculated that the virus spreads into the eye from the optic nerve and along retinal ganglion cell axons.
It is also possible that the entry into the eye is haematologic, they wrote, but they did not find any signs of associated vascular involvement, such as vasculitis, vascular occlusions, retinal ischaemia or secondary neovascularisation.
Neurotrophic properties are increasingly being recognised in Ebola, the researchers added. West Nile virus disease, which is caused by a known neurotropic virus, is also associated with retinal lesions in a similar pattern of distribution.
Dr Steptoe and his colleagues found no difference in uncorrected visual acuity between Ebola survivors and controls. In Ebola survivors, the most common cause of visual impairment was white cataract, found in 7.3%.
In addition, hypotony occured in 80% of Ebola survivors. This suggests inadequate aqueous humour production, which could limit the visual potential of an eye through complications such as retinal folds at the macula (i.e., hypotensive maculopathy), the researchers wrote.
However, although the sample sizes were too small to be definitive, the finding that the virus does not necessarily persist in the aqueous humour suggests that cataract surgery may be safe in Ebola survivors with no signs of ongoing inflammation.
Polymerase chain reaction (PCR) analysis of two survivors with white cataract and no anterior chamber inflammation showed no Ebola RNA.
“At present, we would recommend that anterior chamber sampling with [Ebola virus] PCR and a negative result should precede cataract surgery,” the researchers wrote.
However, cataract surgery might be challenging and visual outcomes disappointing in cases of secondary hypotony, they noted.
They acknowledged two limitations to their study. Firstly, the Ebola survivors and the controls were not matched, and there were different age and sex ratios in the two groups. Secondly, the researchers used Ebola centre treatment discharge cards to identify survivors, and these have sometimes been forged.