Shani in the 8th house increases longevity but may give eye troubles. for Sagittarius Lagna Shani in 8th in its Dasha and antardasha of the sun has given rise to some rare eye complications. 

The fact that the sun is the 8th lord from the 2nd indicates trouble. The sun is also Karak for eyes . and the Dasha of the inimical planet Shani has triggered an event. 

The key fact also is that Shani happens to be 2nd lord indicting eyes and 3rd lord indicating some trouble to it