Images are widely used in automatic text simplification systems, Picture Exchange Communication Systems (PECS) and human-produced easy-read documents, in order to make text more accessible for people with various types of disabilities, including Autism Spectrum Disorder (ASD). People with ASD are known to experience difficulties in reading comprehension, as well as to have unusual attention patterns, which makes the development of user-centred tools for this population a challenging task. This paper presents the first study to use eye-tracking technology with ASD participants in order to evaluate text documents. Its aim is two-fold. First, it evaluates the use of images in texts and provides evidence of a significant difference in the attention patterns of participants with and without autism, with the autistic participants focusing on images more than the non-autistic ones. Sets of two types of images, photographs and symbols, are compared to establish which ones are more useful to include in simple documents. Second, the study evaluates human-produced easy-read documents, as a gold standard for accessible documents, on 20 adults with autism. The results provide an understanding of the perceived level of difficulty of easy-read documents according to this population, as well as the preferences of autistic individuals in text presentation. The results are synthesized as set of guidelines for creating accessible text for autism.