 Very little is known about the symptoms and frequency of reading problems associated with visual discomfort. Conlon et al 1999 has conducted the only study that has used a symptom questionnaire with published validity and reliability. The scale consists of 23 items that sample a wide variety of visual symptoms associated with reading using a four point rating scale. The internal consistency of the scale was high Cronbach alpha .91, and several experiments confirmed the scale could predict unpleasant symptom frequency and performance efficiency while reading. 