At 8 months, Samuel was still developing normally apart from his photosensitivity and pendular nystagmus. An electroretinogram (ERG) was ordered to confirm the diagnosis. An ERG is a diagnostic test that measures the electrical activity of a person’s rods and cones in the retina. The rods and cones are two types of light receptor cells that are responsible for night (rods), daylight (cones), and color vision (cones). In an ERG, an electrode is placed into the person’s eye, similar to a contact lens, and held open by a device called a retractor. The electrical activity of the retina is measured by the electrode in response to flashes of bright light. The test is done in normal room light and in dimmed light. Due to the complex nature of the test for an 8-month-old, the parents declined the ERG and agreed to proceed with genetic testing. Genetic testing revealed that Samuel had a defect in the CNGB3 gene, which is the most common gene mutation associated with achromatopsia.
Top picture: eyes in indoor lighting. Bottom picture: same child in low lighting.
Achromatopsia, also called rod monochromatism, is a rare, congenital, autosomal recessive retinal disorder that affects 1/30,000 to 1/50,000 people worldwide.3 It is characterized by severe photosensitivity, reduced visual acuity, color blindness, and pendular nystagmus.4 Two general forms of achromatopsia exist: complete and incomplete achromatopsia. These conditions are distinguished by their ability to discriminate color and visual acuity. Complete achromats have complete absence of color vision (seeing only black, white, and shades of gray) and usually have visual acuity of 20/200 under optimal low-light conditions.5 Incomplete achromatopsia is a milder form in which there are some functioning cone cells in the retina that allow a person to discriminate a small amount of color vision. Compared with a complete achromat, incomplete achromats have better visual acuity ranging from 20/60 to 20/100.5
Six genes have been associated with achromatopsia: CNGA3, CNGB3, GNAT2, PDE6C, PDE6H, and ATF6.6 The most prevalent mutation is found in the CNGB3 gene, followed by CNGA3.7 The CNGB3 is highly prevalent among the Pingelapese islanders, who live on the Eastern Caroline Islands of Micronesia and have been the basis of the popular book, The Island of the Colorblind, by Dr Oliver Sacks.
Achromatopsia is diagnosed clinically by medical history, ophthalmologic examination, psychophysical examination (visual acuity, visual field, and color vision), and ERG.6 Genetic testing confirms the clinical diagnosis and allows for family studies.6 Achromatopsia is generally a stable disease, but progression to macular degeneration has been observed in rare cases.3
To date, there is no cure for achromatopsia. Therefore, treatment is focused on the debilitating symptoms of photosensitivity and improving visual acuity with low-vision rehabilitation. Treatment goals should be aimed at maximizing quality of life, promoting independence, and ensuring safety for the patient. Photosensitivity is reduced through wearing dark, special filter glasses or red-tinted contact lenses, which may also improve vision acuity.3 Prescribing glasses to correct hyperopia, myopia, and astigmatism can improve vision but is not able to restore an individual’s eyesight to normal 20/20 vision. Low-vision aids include high-powered magnifiers, telescopes, closed circuit television systems (CCTV), and video magnification.3 Additional considerations for school-age children must be considered for special accommodations.
The same boy at age 5 with red-tinted sunglasses.
A referral to special education for an individual education plan (IEP) and consultation with an orientation and mobility specialist are needed due to absence of color vision, impaired visual acuity, and photosensitivity (see the Achromatopsia resources). As symptoms appear during infancy, clinicians should involve the caregivers in the treatment plans for optimal short- and long-term outcomes. With rapid advances in technology and increased social connectivity through Facebook and Yahoo groups where insights are shared and support is received, many achromats live fulfilling lives. Promising clinical phase I/II safety trials are under way for gene replacement therapy for CNGA3 and CNGB3 genes, which may mean hope for a cure for achromatopsia.8
- Low Vision Centers of Indiana
- American Academy of Pediatric Ophthalmology and Strabismus (AAPOS)
- National Library of Medicine
Patient and Family focus:
- Achromatopsia information
- Achromatopsia Facebook page
- Achromatopsia Support Network group on Facebook
- Achromatopsia Yahoo Groups: Forum for parents of children with Achromatopsia; general support group for Achromatopsia
Chin Hwa Dahlem, PhD, FNP-C, FAANP, is a clinical assistant professor at the University of Michigan School of Nursing in Ann Arbor. Michelle Pardee, DNP, FNP-BC, is a clinical assistant professor and FNP program coordinator at the University of Michigan School of Nursing in Ann Arbor. April Bigelow, PhD, ANP-BC, AGPCNP-BC, is a clinical associate professor and ANP program coordinator at the University of Michigan School of Nursing in Ann Arbor.
- Ehrt O. Infantile and acquired nystagmus in childhood. Eur J Paediatr Neurol. 2012;16(6):567-572. doi 10.1016/j.ejpn.2012.02.010.
- Papageorgiou E, McLean RJ, Gottlob I. Nystagmus in childhood. Pediatr Neonatol. 2014;55(5):341-351. doi: 10.1016/j.pedneo.2014.02.007.
- Kohl S, Hamel C. Clinical utility gene card for: Achromatopsia – update 2013. Eur J Hum Genet. 2013;21(11). doi:10.1038/ejhg.2013.44.
- Michaelides M, Hunt DM, Moore AT. The cone dysfunction syndromes. Br J Ophthalmol. 2004;88(2):291-297.
- Windsor RL, Windsor LK. Understanding Achromatopsia. Retrieved from http://www.lowvision.org/achromatopsia_and_color_blindnes.htm
- Kohl S, Jägle H, Wissinger B. (2016). Achromatopsia. Gene Reviews. 2004. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK1418/
- Zobor D, Zobor G, Kohl S. Achromatopsia: on the doorstep of a possible therapy. Ophthalmic Res. 2015;54(2):103-108.
- National Institutes of Health. Clinical Trials.gov. CNTF Implants for CNGB3 Achromatopsia. 2014. Retrieved from https://clinicaltrials.gov/ct2/show/NCT01648452?cond=%22achromatopsia%22&rank=1