Abnormalities in eyes of FA carriers do not affect their vision: Study
Carriers generally do not show overt symptoms but may have eye abnormalities
Abnormalities in the light-sensing cells of the eyes are detectable in carriers of Friedreich’s ataxia (FA), but do not appear to affect parts of the pathways that are essential for vision so carriers do not experience visual impairment.
That’s according to a study, “Retinal and Visual Pathways Involvement in Carriers of Friedreich’s Ataxia,” which was published in the journal Diagnostics.
Friedreich’s ataxia often affects the eyes
People with FA commonly experience some form of disease involvement that affects the eyes. Ophthalmological evaluations in patients frequently reveal abnormalities in eye movements, as well as damage to the retina (the region of the eye that houses light-sensing cells) and the optic nerve, which connects the eyes to vision-processing centers in the brain.
FA is caused by mutations in the FXN gene, which provides instructions for making the frataxin protein. Everyone inherits two copies of FXN, one from each biological parent. FA is an autosomal recessive disease, meaning that full-blown disease will only develop if both copies of FXN carry a mutation.
People with one mutated copy of FXN (and one other healthy copy) are called carriers, because they will not develop FA but may pass on the disease-causing mutation to their biological children. While carriers generally do not develop overt symptoms, it’s not known whether they may be prone to subtle abnormalities in the structure of eye tissue like those seen in people diagnosed with the disease.
To learn more, a team of scientists in Italy and Poland conducted detailed eye exams on 10 carriers of FA, as well as 35 control participants who did not have FA and were not carriers.
“In this observational study, we investigated, for the first time, the function and the morphology of the retina and of visual pathways in healthy carriers of [FA],” the team wrote.
Results showed that FA carriers did not show significant impairment in measures of visual acuity compared with controls.
The structure of the retina, optic nerves, and surrounding tissue generally appeared normal in the carriers as well. However, assessments of electrical activity in the retina in these regions showed some abnormalities.
Optic nerve activity abnormal in FA carriers
Optic nerve activity was abnormal in FA carriers, who, according to measures, have reduced function of rods — one of the two main types of light-sensing cells in the eyes, the other being cones. Rods are particularly good at detecting shapes and texture, whereas cones are specialized to detect color.
Of note, assessments of the macula — the central and most sensitive portion of the retina — showed no structural abnormalities in carriers. “Therefore, all that described suggests that, in carriers of [FA], there exists a functional retinal and macular impairment that is not related to structural macular abnormalities,” the investigators wrote.
“Our data suggest that, in [FA carriers], a dysfunction of … retinal elements without morphological macular impairment may occur,” the team concluded.
“All these observations, describing retinal and visual pathways impairment in [FA carriers], need to be confirmed by clinical studies with larger numbers of subjects, as well as by research investigations clarifying the role of frataxin in the visual system,” they added.
About the Author
