You are an excellent assistant at finding disabilities in Spanish biomedical abstracts. You will be doing Named Entity Recognition for these disabilties and you must respond with each exact phrase as it appears in the article. If it appears multiple times, respond with each phrase separated by newline character. If there are no disabilities, respond with NA.

A disability is defined as:
a physical or mental condition that limits a person's movements, senses, or activities.


Abstract:

Abstract Purpose To determine the prevalence of visual impairment attributable to refractive error and other causes in a youthful Ghanaian population . Methods A prospective survey of all consecutive visits by first - year tertiary students to the Optometry clinic between August , 2013 and April , 2014 . Of the 4378 first - year students aged 16–39 years enumerated , 3437 ( 78 .5% ) underwent the eye examination . The examination protocol included presenting visual acuity ( PVA ) , ocular motility , and slit - lamp examination of the external eye , anterior segment and media , and non - dilated fundus examination . Pinhole acuity and fundus examination were performed when the PVA ≤ 6/12 in one or both eyes to determine the principal cause of the vision loss . Results The mean age of participants was 21 .86 years ( 95% CI : 21 .72–21 .99 ) . The prevalence of bilateral visual impairment ( BVI ; PVA in the better eye ≤6/12 ) and unilateral visual impairment UVI ; PVA in the worse eye ≤6/12 ) were 3 .08% ( 95% CI : 2 .56–3 .72 ) and 0 .79% ( 95% CI : 0 .54–1 .14 ) , respectively . Among 106 participants with BVI , refractive error ( 96 .2% ) and corneal opacity ( 3 .8% ) were the causes . Of the 27 participants with UVI , refractive error ( 44 .4% ) , maculopathy ( 18 .5% ) and retinal disease ( 14 .8% ) were the major causes . There was unequal distribution of BVI in the different age groups , with those above 20 years having a lesser burden . Conclusion Eye screening and provision of affordable spectacle correction to the youth could be timely to eliminate visual impairment .
visual impairment
vision loss
bilateral visual impairment
BVI
unilateral visual impairment
UVI
BVI
UVI
BVI
visual impairment