usually it starts or manifest after puberty and progresses  slowly but if it progresses  rapidly  then  it is more  harmful.  you notice only diminished  vision. it is the  ophthalmologist  who diagnoses  it.a person  may  enjoy  good  vision  with specs inspite  of keratoconus.the exact cause  needs  further  research  but  mostly  it is congenital  weakness of cornea. increased  IOP may be damaging and vision threatening. in terminal stages  when  useful vision  has gone, the best  treatment  is penetrating keratoplasty (cornea translation )

To answer all..let me give it one by one. 1. Keratoconus worsen vision rapidly if detected at early age. It depends on the severity of keratoconus and age of a person at the diagnosis of disease. If it is mild (grade 1) keratoconus detected in 20's then definitely rate of progression is slow. 2. Symptoms: frequent change in glass number. Not comfortable with glasses. Few patients have eye rubbing. 3.Keratoconus in early stages do not show much symptoms..only sometimes not so clear vision even with glasses. Doctor need to do certain tests to confirm diagnosis of keratoconus. 4. There is no protein deficiency detected in keratoconus patients. In the treatment of keratoconus we strenghten the cornea by cross linking the collagen so that further deterioration is prevented. 5.High IOP is not risk factor for keratoconus; but frequent eye rubbing is. Hope this has answered most of your questions. Regards.