76. Mentzer index

The Mentzer index is used to differentiate iron deficiency anemia from beta thalassemia.

If a CBC indicates microcytic anemia, these are two of the most likely causes, making it necessary to distinguish between them.

It is calculated from the results of a complete blood count. If the quotient of the mean corpuscular volume divided by the red blood cell count is less than 13, thalassemia is more likely.

If the result is greater than 13, then iron-deficiency anemia is more likely.It was described in 1973.This test helps in differentiating iron deficiency from thalassemia.

In iron deficiency, the marrow cannot produce as many RBCs and they are small (microcytic), so the RBC count will be low along with the MCV, and as a result, Mentzer's index is not as low, greater than 13, Comparatively, in thalassemia, which is a disorder of globin synthesis, RBC production is preserved, but the cells are much small and fragile. So the RBC count is normal with a low MCV. Thus the Mentzer's index is less than 11.

It is also important to note that the test has a high specificity and low sensitivity. In a lot of cases, the index may fall in between 11 and 13, such cases a peripheral blood smear and iron studies would help to differentiate iron deficiency from thalassemia.

75 - 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 hereditary 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.