Silver Eye

Symptoms

Silver Eye is a discolouration that first starts with the iris and eventually spreads towards the pupil. It's a mostly physiological disorder. While eyesight is not directly affected by this, most individuals do report increased photosensitivity.
While some viral and fungal infections show similar symptoms, Silver Eye is considered to be strictly genetical. Addiction to some toxicological substances are believed the accelerate the disorder, either by setting in at an earlier age or the speed at which the discolouration occurs.
Initial onset in the iris usually occurs between 55-60 years of age, with the pupil turning white around 70.  

Physiology

It is still not understood why eyesight remains relatively unaffected. The white discolouring is believed to be cause by the reflection of light . However this fails to directly explain why photosensitivity increases among subjects.
Due to the complete discolouration, it's impossible to directly observe changes of the pupil depending on light intensity. Researchers at the Petrian University Of Katonice are looking into the detection of microtwitches cause by the eye when reacting to light and how this might be related to the contraction or expansion of the pupil.  

Silver Eye In Literature

The diagnosis of Silver Eye has increased within the last 60 years. However this is believed to be correlated with the general increase in life expectancy and a decrease in possible trauma affecting the eye at a younger age.
The current view on this affliction has also led to a literary hypothesis regarding the recurring imagery of sages, wizards and witches. These archetypes are frequently shown to have white eyes.
It was a common superstition that the elderly, who managed to reach a significant older age, had knowledge far beyond that of most people or that they even dabbled in magic. The individuals who happened to have the required genetic trait, might have developed the same symptoms as Silver Eye.
The expected photosensitivity also goes to explain, why these people were often portrayed to be living in caves, dense forest or dimly lit hovels.