The illness will result in total blindness if (it is) left untreated.

It does not affect peripheral vision, but the loss of clear central vision can rob a person of the ability to read, drive and recognise people's faces even without causing total blindness.

Milton has his hero, Samson, bewailing the fact of his blindness: "o dark, dark, dark, amid the blaze of noon irrecoverably dark, total eclipse without all hope of day!"