Sun in the twelfth house is in the house of losses and in the house which belongs to his arch-enemy Saturn. Having said that Sun is associated with soul and self-realization. Twelfth house is the house of moksha where you get liberation from life and death. Self-realization is the key to achieving moksha. And Sun in its placement in the twelfth house grants the native the much needed self-realization. Of course from material perspective this placement of Sun may not be that ideal but on a spiritual plane it is a great placement. 

    According to B. V. Raman: "Native may engage in a not so pleasant occupation. He may get below par success and can feel neglected by others. He will suffer from loss of some limb and have a weak eye-sight. He would however be energetic". Sun is associated with eyes and in a dushamsthana it is given that eyesight maybe a bit weak. Both Mercury and Venus travel very close to the Sun. Normally what has been observed is Sun+Venus in the twelfth house is very likely to cause divorce for natives. Sun is associated with self-realization while Venus is associated with romance. Self-Realization often brings an end to romance and especially in the twelfth house which deals with losses. Essentially when we lose something precious is the time we gain self-realization. Sun+Mercury on the other hand may not be that bad if Venus is away. Sun also rules over health and will power so both are likely to be weak especially if ascendant and ascendant lord are also weak.

    Not the best place for Sun from a materialistic viewpoint. But not a bad place for it if spiritual advancement is considered. Not everyone is into spirituality so the need arises to cure the ill-effects of Sun. Praying to Lord Vishnu and chanting the Vishnu Sahasranaam may help. If romance and sex are lacking in marriage life pray to Kamdev and recite the Kamdev Gayatri. Trying anulom vilom and other yogas for eye sight, food rich in Vitamin A like carrots, spinach, butter, fish, cod-liver oil, Green vegetables would be ideal especally for the weak eyes