Wuxia fiction has no shortage of blind characters; there's scarcely a wuxia story out there that doesn't feature at least one blind character.
HSDS, however, featured an extraordinary number (even for a wuxia story) of blind characters, including an inordinate number of characters who became blind during the story. The blind characters in HSDS included Tse Tsun, Sing Kwun, Shaolin monks Yeun Yum and one of the Dao-generation elders (one eye each), and Monk Pang (also one eye) of the Ming Cult. Bak Gwai Sau of the Heavenly Eagle Sect even tried to evade pursuers from the Kunlun and Hung Dung sects by pretending to be a blind man.
That much blindness in one story convinces me that Jin Yong had some intentional leitmotif or theme going on with blindness here.
In fact, being physically impaired seems to be a leitmotif of HSDS in general; in addition to all those blind people listed above, we also have the following disabilities: Yu Doi Nam was paralyzed for twenty years (and never regained full mobility); Yan Lei Ting suffered similar crippling injuries, but recovered thanks to Chiu Mun's black jade ointment; Granny Golden Flower's lungs were impaired by her dip in the icy pool during her youth; Yan Lei was disfigured by practicing Thousand Poisonous Spider Hands; Ah Dai had his arm cut off by Cheung Mo Gei, and Cheung also crippled Ah 2 and Ah 3 to avenge their crippling of his Mo Dong Sect martial uncles; Beggar's Union Chief Shih For Lung was paralyzed by a failed attempt to learn Hong Lung 18 Palms; Sung Ching Sheu was critically wounded and rendered a quadriplegic vegetable by Yu Lin Chou.
Wuxia fiction in general has no shortage of characters who are maimed, but HSDS features such an inordinate number of them that I wonder if Jin Yong wasn't trying to communicate some theme to the audience.