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Ocular System

Oguchi’s disease

Congenital stationary night blindness (CSNB) variant caused by a disruption in the steps of inactivation of rod phototransduction associated with fundus discoloration and abnormally slow dark adaptation after light exposure, along with characteristic electroretinographic (ERG) abnormalities.

Congenital stationary night blindness (CSNB) variant caused by a disruption in the steps of inactivation of rod phototransduction associated with fundus discoloration and abnormally slow dark adaptation after light exposure, along with characteristic electroretinographic (ERG) abnormalities.

  • Autosomal recessive inheritance
  • M/C cause of congenital stationary night blindness (CSNB) in the Japanese population

History:

The disease was first reported by Oguchi in 1907 as a variant form of congenital stationary night blindness (CSNB) and was later characterized phenotypically by Mizuo in 1913 , who demonstrated the Mizuo-Nakamura phenomenon in affected individuals. In this test after 2–3 h of dark adaptation of the eyes, the diffused yellow/grey discoloration of the fundus returns to normal, along with the reappearance of rod function. The discoloration of the fundus reappears shortly after reexposure to light. Oguchi disease has been shown to be more common in the Japanese population compared to other populations. In addition to the typical Oguchi disease, variant forms have also been reported without the typical Mizuo-Nakamura phenomenon and variable fundus appearances and ERG patterns.


Pathophysiology

Rhodopsin kinase (GRK1) and Arrestin (SAG) are two genes which act in sequence to deactivate rhodopsin to stop the phototransduction cascade. Photoactivated rhodopsin is recognized by rhodopsin kinase, which phosphorylates serine and threonine residues near rhodopsin’s carboxy terminus. Arrestin then forms a complex with phosphorylated rhodopsin, and this complex prevents further interaction of the activated rhodopsin with transducin. Mutations in either the rhodopsin kinase gene or the arrestin gene cause a recessive form of stationary night blindness called Oguchi’s disease.


Clinilcal features

  • Static nyctalopia (night vision) since childhood
  • Preservation of vision in bright light.

Diagnosis

Mizuo phenomenon:

Golden or gray-white discoloration of the fundus that disappears in the dark-adapted state and reappears shortly after the onset of light.
Dark adaptation test of the patient. Fundus photographs of the patient before (A) and after (B) dark adaptation. The fundus appearance was characteristic of Oguchi disease with grayish-yellow discoloration that had normal appearance after 2–3 h of dark adaptation. | Waheed, N. K., Qavi, A. H., Malik, S. N., Maria, M., Riaz, M., Cremers, F. P., Azam, M., & Qamar, R. (2012). A nonsense mutation in S-antigen (p.Glu306*) causes Oguchi disease. Molecular vision, 18, 1253–1259.

Electroretinogram (ERG):

  • Negative waveform morphology with non-recordable single flash rod response (CHARCTERISTIC)
  • Negative-positive combined response
  • Normal photopic response
Electroretinograms of a normal individual and patients with forms of stationary night blindness. The tracings in the top row are the responses to single flashes (repeated every 2 seconds, or 0.5 Hz) of blue light that is so dim that only rods are stimulated. The middle row shows the responses to 0.5-Hz, bright, white flashes that stimulate both rods and cones. The bottom row shows the responses to bright, white light flashing 30 times per second (30 Hz); cones but not rods elicit individual responses to light flashing at this frequency. Thus, going from the top to bottom rows, one observes normal rod-isolated responses, combined rod-plus-cone responses, and cone-isolated responses. The time of the light flashes is denoted by the vertical dashed line in the top and middle rows and by the solid vertical lines within the tracings of the bottom row. The letters “a” and “b” in the normal rod-plus-cone electroretinogram (left column, middle row) label the a-wave and b-wave, respectively. The arrows in the tracings of the bottom row denote the cone peak implicit times (that is, the time interval between a light flash and the corresponding peak amplitude). In all tracings, two or three consecutive sweeps are superimposed. The calibration symbol in the lower right corner designates 50 ms horizontally and 100 μV vertically. The column headings refer to the genetic defect causing each patient’s night blindness. Note that the patients with rhodopsin, transducin, and rhodopsin kinase mutations have no observable rod b-waves with these test conditions, whereas the patient with a defective 11-cis RDH (fundus albipunctatus) has a subnormal rod b-wave that becomes normal in amplitude after 5 hours of dark adaptation. Mixed rod-plus-cone responses to 0.5-Hz flashes of bright white light (middle row) are without a prominent cornea-positive b-wave (rhodopsin and rhodopsin kinase cases) or have subnormal b-waves (transducin) except for fundus albipunctatus where the rod-plus-cone b-wave is normal. The rod-plus-cone electroretinograms in fundus albipunctatus would be subnormal after 45 minutes of dark adaptation if the dark-adaptation period had been preceded by exposure to intensely bright light that would bleach a large proportion of the patient’s rhodopsin. In all of these forms of stationary night blindness, cone electroretinograms in response to 30-Hz white flickering light are normal or near-normal in amplitude and have normal peak implicit times (that is, 32 ms or less). | Dryja, T. P. (2000). Molecular genetics of Oguchi disease, fundus albipunctatus, and other forms of stationary night blindness: LVII Edward Jackson Memorial Lecture. American Journal of Ophthalmology, 130(5), 547–563. https://doi.org/10.1016/S0002-9394(00)00737-6

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