Comparing the Mass Blindness-Deafness spell description in lore to the Sunburst description it seems strange that both are 8th level spells. Sunburst is more flexible (blinds, causes a little damage to undead, and is extremely effective against undead), sunburst causes permanent blindness versus a round per level for mass blindness-deafness, and sunburst is a gigantic area of effect versus 10 ft radius for mass blindness-deafness. On the plus side for mass blindness-deafness, it does cause deafness too.
I don't recall ever seeing anyone use this spell and it seems like it has the potential to be a good spell with a little tweaking.
I think that the area of effect for mass blindness-deafness should be greatly expanded to match sunburst and it seems like a will save against illusion would be more realistic than the current fortitude save.