====== Achromatopsia ======

====Main Features====
  * Reduced vision due to lack of functioning cones
    * Vision usually 20/200 with complete color blindness in complete forms 
    * Incomplete forms may have better vision and some color vision
  * Nystagmus that may improve with age
  * Central relative scotoma with normal peripheral visual fields
  * Complete and Incomplete forms
  * Usually stable but some see slow worsening of visual acuity and macular atrophy
====Distinguishing Features====
  * Photophobia at birth or early infancy 
  * Better vision in dim illumination
  * Sluggish pupil responses with paradoxical constriction in the dark 
  * Usually normal fundus appearance 
    * OCT may show ellipsoid zone disruption or absence, outer retinal atrophy and RPE loss
  * ERG 
    * lack of cone function- 30 Hz flicker and single flash photoptic waveform is small and delayed 
    * normal ROD function- normal dark adapted dim and bright flash waveforms
====Differential Dx====
  * [[congenital_stationary_night_blindness|Congenital Stationary Night Blindness]]
  * [[leber_congenital_amaurosis|Leber Congenital Amaurosis]]
  * [[retinitis_pigmentosa|Retinitis Pigmentosa]]
  * Idiopathic Nystagmus Syndrome 
====Pathogenesis====
  * 1 in 30,000 live births
  * Recessively inherited mutation in a gene that codes for a part of the cone phototransduction pathway. 
  * 70-80% from mutations in the following genes: CNGA3 and CNGB3 
  * 1-2% from mutations in GNAT2, PDE6C, PDE6H, ATF6 
====Treatment====
  * Supportive care
  * Sunglasses
====Resources====
  - [[https://www.clinicalkey.com/#!/content/book/3-s2.0-B9780702082986000457#hl0000659|Taylor and Hoyt Textbook article]]
  - [[https://www.tandfonline.com/doi/full/10.1080/13816810.2017.1418389 |Hirji N. et al. Achromatopsia: clinical features, molecular genetics, animal models and theraputic options. Ophthalmic Genetics 2018;39(2):149-157]] [[https://1drv.ms/b/c/31d83ae8e55e0542/EdksFbEMfIBMkILEHEs01NcB3l10U7_oZE0oUhaTNeVNVA?e=aWa9GE|_]]

{{tag>inherited_retinal_disease retina}}