What is Mizuo phenomenon is seen in: and explain in detail?
Ans. b. Oguchi's disease Mizuo phenomenon is seen in Oguchi \ disease."In Oguchis disease the characteristic golden yellowish metallic sheen (color) of posterior pole (fundus) in light adapted state reverts to normal after prolonged dark adaptation, a phenomenon described by and named after Japanese ophthalmologist Mizuo Re-exposure to light results in the return of golden yellow metallic sheen.** Female carriers of X-linked (XL) retinitis pigmentosa may have normal fundi or show a golden metallic (tapetal) reflex at macula and/or small peripheral patches of hone spicule pigmentation. The inverse Mizuo phenomenon seen in XL-RP is characterized by appearance of golden sheen in dark (hut no golden sheen in light)."Oguchi's Disease* Oguchi's disease is a rare autosomal recessive trait characterized by congenital stationary night blindness and a unique morphological and functional abnormality of the retina.* Show Mizuo phenomenon^* Mizuo phenomenon: Fundus is golden yellow in light adapted state which becomes normal after prolonged dark adaptation. Reexposure to light results in the return of the metallic y ellow sheeny.* Rod function is absent after 30-minutes of dark adaptation but recovers to a near normal level after a long period of dark adaptation (i.e. -- normal rod thresholds reached only after 4 hours or longer instead of normal 30 minutes).Etiopathogenesis:* A null allele in genes for each of rhodopsin kinase and arrestin (proteins responsible for terminating phototransduction cascade) is responsible for Oguchi's disease.* Therefore, the persistent low level of light may desensitize the rods continually.* Mizuo phenomenon suggest an abnormality in rod pigment, rhodopsin.* Cone function is normal because cone adaptation, final cone thresholds and photopicERG response are normal.* Rod function is abnormal with delayed dark adaptation and scotopic ERG showing only a small electronegative response, even when the rod threshold have reached normal.Clinical Features:* Patients have non-progressive night blindness since young childhood writh normal day vision, but they often claim improvement of light sensitivities w hen they remain long in the dark environment* The fundus oculi presents a most peculiar appearance.