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Bradyopsia: for professionals

Overview

PrevalenceExtremely rare; precise prevalence unknown
InheritanceAutosomal recessive
Genes Involved (OMIM No.)RGS9 (#607814), R9AP (#610924)
SymptomsDelayed adaptation to changes in light intensity, Photophobia, Reduced visual acuity, Normal colour vision
Ocular FeaturesNormal fundus appearance
Key InvestigationsOcular
Ophthalmic examination, Optical coherence tomography (OCT), Fundus autofluorescence (FAF), Electroretinogram (ERG), Electro-oculogram (EOG)
Molecular DiagnosisWhole genome sequencing with retinal panel, or targeted sequencing of RGS9 and R9AP
ManagementOcular: Regular ophthalmic monitoring, Tinted glasses or contact lenses, Low vision aids

Systemic: Genetic counselling, advice on family planning, emotional and practical support
Therapies under ResearchResearch on molecular mechanisms, potential gene therapies, and diagnostic techniques

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Clinical phenotype

Bradyopsia is a rare autosomal recessive retinopathy characterised by a delayed adaptation to changes in luminance levels. This condition primarily affects the visual system, causing significant functional impairment.1

Presenting features

Ocular:

  • Visual disturbances: Patients experience difficulty in adapting to sudden changes in light intensity, resulting in delayed dark-to-light and light-to-dark adaptation.2,3
  • Photophobia: Increased sensitivity to light.
  • Reduced visual acuity: Typically, moderate reduction in central vision.
  • Normal colour vision: Unlike other retinal dystrophies, colour vision remains intact.
  • Normal fundus appearance: Clinical examination usually reveals no abnormalities in the retinal appearance.

Genetics

Genes: RGS9 (OMIM #607814) and R9AP (OMIM #610924).

  • Inheritance Pattern: Autosomal Recessive.
  • Function: Both genes are involved in the rapid deactivation of the phototransduction cascade. RGS9 encodes a GTPase-activating protein, and R9AP encodes a membrane anchor protein that enhances the function of RGS9.1,4

    Further information about each gene can be found on OMIM and Medline Plus.

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    Key investigations

    Ocular

    1. Ophthalmic Examination: Moderate reduction in visual acuity, photophobia, and normal fundus.
    2. Optical Coherence Tomography (OCT): Normal retinal structure.
    3. Fundus Autofluorescence (FAF): Typically normal autofluorescence.
    4. Electrophysiological Testing:
      • Electroretinogram (ERG): Pathognomonic delayed recovery of cone responses. Normal dark-adapted responses to red flash (DA red ERG). Dark-adapted bright flash (DA 10.0) ERG appears normal initially but shows attenuation on subsequent flashes unless a prolonged interstimulus interval (2 minutes) is used.5
      • Electro-oculogram (EOG): May show normal light peak to dark trough ratio.
    5. Genetic testing: whole genome sequencing with retinal panel

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    Diagnosis

    A definitive diagnosis of bradyopsia involves clinical evaluation, detailed electrophysiological testing, and genetic testing to identify mutations in the RGS9 or R9AP genes.

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    Differential Diagnoses

    Differential diagnoses include incomplete achromatopsia and blue cone monochromatism, which also exhibit cone dysfunction but have distinct electrophysiological and clinical features.

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    Management

    The management of bradyopsia focuses on symptom alleviation and maximising residual visual function.

    Ocular

    1. Regular ophthalmic monitoring: To monitor visual function and photophobia.
    2. Tinted glasses or contact lenses: To reduce photophobia and improve visual comfort in bright conditions.6
    3. Low vision aids: To assist with daily activities and improve quality of life.

    Family management and counselling

    Patients and families require genetic counselling and can seek advice for family planning including prenatal testing and preimplantation genetic diagnosis.

    Emotional and social support

    Genetic counsellors and Eye Clinic Liaison Officers (ECLOs) act as an initial point of contact for newly diagnosed patients and their parents in clinic. They provide emotional and practical support to help patients and parents deal with the diagnosis and maintain independence. They work closely with the local council’s sensory support team and are able to advise on the broad range of services provided, such as visual rehabilitation, home assessment, work and access to qualified teachers for children with visual impairment (QTVI) among other services.

    Related links

    Referral to a specialist centre

    In the UK, patients should be referred to their local genomic ophthalmology (if available) or clinical genetics services to receive comprehensive management of their condition (genetic testing and genetic counselling) and to have the opportunity to participate in clinical research.

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    Current research

    Research on bradyopsia is focused on understanding the molecular mechanisms, developing potential gene therapies, and improving diagnostic techniques. Investigations into gene supplementation and other therapeutic approaches aim to improve the quality of life for affected individuals.

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    Further information and support

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    References

    1. Strauss RW, Dubis AM, Cooper RF, Ba-Abbad R, Moore AT, Webster AR, et al. Retinal architecture in RGS9- and R9AP-associated retinal dysfunction (Bradyopsia). Am J Ophthalmol 2015;160(6):1269–75.
    2. Cheng JY, Luu CD, Yong VH, Mathur R, Aung T, Vithana EN. Bradyopsia in an Asian man. Arch Ophthalmol. 2007 Aug;125(8):1138-40. doi: 10.1001/archopht.125.8.1138. No abstract available. 
    3. Hartong DT, Pott JW, Kooijman AC. Six patients with bradyopsia (slow vision): clinical features and course of the disease. Ophthalmology. 2007 Dec;114(12):2323-31. doi: 10.1016/j.ophtha.2007.04.057. Epub 2007 Sep 12. Michaelides M, Li Z, Rana NA, Richardson EC, Hykin PG, Moore AT, Holder GE, Webster AR. Novel mutations and electrophysiologic findings in RGS9- and R9AP-associated retinal dysfunction (Bradyopsia). Ophthalmology. 2010 Jan;117(1):120-127.e1. doi: 10.1016/j.ophtha.2009.06.011. Epub 2009 Oct 8. 
    4. Nishiguchi KM, Sandberg MA, Kooijman AC, Martemyanov KA, Pott JW, Hagstrom SA, Arshavsky VY, Berson EL, Dryja TP. Defects in RGS9 or its anchor protein R9AP in patients with slow photoreceptor deactivation. Nature. 2004 Jan 1;427(6969):75-8. doi: 10.1038/nature02170. 
    5. Vincent A, Robson AG, Holder GE. Pathognomonic (diagnostic) ERGs. A review and update. Retina. 2013 Jan;33(1):5-12. doi: 10.1097/IAE.0b013e31827e2306.
    6. Black GC, Ashworth JL, Sergouniotis PI, editors. Clinical ophthalmic genetics and genomics. Academic Press; 2022 Jan 18.

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    Updated on June 3, 2024
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