40 - Mizuo phenomenon

MIZUO PHENOMENON is a feature of Oguchi's disease.

Oguchi's disease is a peculiar and distinctive bilateral condition, congenital and stationary in type and heriditary in nature. It is characterized by structural anomalies in the retina and a retardation of dark adaptation amounting to night blindness.

Features of Oguchi's disease:

The fundus oculi presents a most peculiar appearance. The posterior pole and in many cases the whole of fundus, instead of having a normal orange-red colour, presents a curious shining greyish-pink background, on which the retinal vessels stand out sharply. The vessels appear dark with little distinction between the arteries and the veins. The finer divisions of the blood vessels can be easily followed to their finest ramifications. At places a dark shadow or a bright white line may be seen alongside the blood vessel.

In addition to the above mentioned appear­ances, other features are:
1. The choroidal vessels are seen less dis­tinctly.
2. The peripheral blood vessels have a very rough appearance and show pigment­like blotches on or near them. But there is no actual pigmentary disturbance.
3. Many vessels in the periphery look wider and fainter and tend to be lost in the shining greyish-pink background. This appearance has been termed by us as "Washed out appearance".

The most interesting feature of this disease in well marked cases is the reversal of all the features described above, if the patient sits in the dark for about one hour. This is called Mizuo's phenomenon.