In this second part in our series about Acquired Color Vision Deficiencies we continue to discuss how color vision can be an early indicator of other ocular diseases. Here we look closer at optic nerve disorders, particularly glaucoma, and how they can lead to significant changes in color vision. Understanding these deficiencies is crucial for early diagnosis and treatment.
Glaucoma and Color Vision
Glaucoma encompasses a group of optic neuropathies characterized by the loss of retinal ganglion cells and the cupping of the optic nerve head. Early research indicated that glaucoma could cause acquired deficiencies in color vision, specifically affecting the M-L (red-green) mechanism. However, it is now recognized that glaucoma might lead to color vision changes, typically first as a deficiency in the S (blue-yellow) mechanism, as demonstrated by conventional color vision tests like the F-M 100-Hue and desaturated D-15.
Over the past three decades, efforts have focused on detecting color vision loss before it becomes apparent through visual field tests, particularly in cases of "preperimetric glaucoma." While color perimetry showed promise as a diagnostic tool, other methods have emerged with superior screening capabilities.
Hereditary Optic Neuropathies
Conditions like dominant optic atrophy, associated with OPA1 gene mutations, exhibit significant variability in color vision deficiencies among affected individuals. Some patients may show symptoms similar to congenital tritanopia, though this connection has been largely dismissed.
Leber hereditary optic neuropathy (LHON), a mitochondrial disorder, typically results in profound vision loss. In its early stages, patients may exhibit M-L mechanism deficiencies, which can serve as an early warning sign. Recent studies have also indicated that asymptomatic carriers of LHON may experience subtle color discrimination impairments, particularly affecting males. Understanding early color perception changes in optic nerve disorders like LHON can provide critical diagnostic insights.
Optic Neuritis
The Optic Neuritis Treatment Trial investigated color vision in 438 participants during acute inflammation and at six months. In the acute phase, a striking 93.2% of patients showed abnormal scores on the F-M 100-Hue test. By six months, this number decreased to 39.4%, with a notable prevalence of S-mechanism deficiencies initially, shifting towards M-L deficiencies over time. A clear correlation was found between visual acuity and color vision abnormalities.
Optic Nerve Compression
Studies on optic nerve compression have produced mixed results. Research involving patients with compressive optic neuropathies revealed no specific impairment in either S or M-L mechanisms. However, a significant percentage of patients demonstrated abnormal color vision, with many showing M-L mechanism deficiencies.
Conclusion
Acquired color vision deficiencies in optic nerve disorders like glaucoma can serve as vital indicators of disease progression. Recognizing these changes early can lead to more effective management and treatment strategies. As research evolves, it will enhance our understanding of these conditions and improve outcomes for affected individuals.
By staying informed about these developments, both healthcare professionals and patients can better navigate the complexities of optic nerve disorders.
References:
Studies mentioned in the blog are referenced from the following main source.
Simunovic, M. P. (2016). Acquired color vision deficiency. Survey of Ophthalmology, 61(2), 132-155. doi:10.1016/j.survophthal.2015.11.004