Stromal dystrophies are popular questions because of the following reasons:

• histologically, the three commonest dystrophies have different

affinities for chemical stains.
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• the dystrophies have different inheritance pattern.

There are many different types of stromal dystrophies but only three are likely to appear in the examination. Their constituents and staining properties can be summed up by the well-known mnemonic of:

Marilyn Monroe Always Gets Her Men in L.A.City Macular dystrophy - Mucopolysaccharide - Alcian blue Granular dystrophy - Hyaline materials - Masson trichrome Lattice dystrophy - Amyloid - Congo Red

This mnemonic is obviously dreamed up by some retired pathologists in LA City. The contemporary ophthalmologists will probably prefer Britney Spear or Carmen Diaz but their initials do not fit !

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Alcian blue The lesions are diffused.

Masson trichrome The lesions are discrete.

Congo red The lesions are discrete.

The above pictures are the typical appearance of the three main stromal dystrophies with special stains. It is important that you examine the actual slides under the microscope as the concentration of the stains used and the microscopic lighting can alter the hue and saturation of the colour. 

The macular dystrophy can also be stained with colloid iron as seen below.
 

If given a slide of lattice dystrophy, you are likely to be asked about the phenomenon of birefringence and dichromism. Birefringence occurs when the tissue stained with Congo red is viewed through a crossed polarizing microscope. Dichromism occurs when the tissue is viewed with polarized light and a green filter.

Birefringence means the amyloid can polarize (split) transmitted light into two beams. Dichromism means two colour: the amyloid turns from red to green depends on the orientation of the tissue under polarized light. The picture below is a section of blood vessels with amyloid viewed with and without polarized light.

 
Common questions:

• What are the presentation of different corneal dystrophies?
• What are the inheritance patterns of different corneal dystrophies?
• What are the different types of lattice dystrophy?

Information about individual conditions can be found in the corneal section of common short cases for MRCOphth.