Contrast sensitivity abnormalities in deaf individuals

Hearing impaired children are heavily dependent on their sense of vision to develop efficient communication skills; any contrast sensitivity defect can negatively impact their lives because they are not able to use auditory stimuli to recognize probable dangers in the world around them. The purpose of this study was to determine the contrast sensitivity abnormalities in deaf individuals.
In this cross-sectional study, contrast sensitivity of 15- to 20-year-old high-school boys with hearing disability from Tehran, Iran were evaluated. Sixty-four eyes were tested for contrast sensitivity and refractive error. All subjects had an intelligence quotient (IQ) >70. We investigated their contrast sensitivity with Vector vision CVS-1000 in 4 different spatial frequencies.
Profound hearing loss was noted in 50% of the subjects. The frequency of contrast sensitivity abnormalities in 4 different spatial frequencies varied between 51.6% and 65.6%. The largest abnormalities were recorded at 18 cycles per degree. Only 12.5% of deaf students had corrected distance visual acuity (CDVA) greater than zero (in LogMAR). The abnormalities in contrast sensitivity showed no correlation with the type or severity of hearing loss.
Hearing impaired boys are at a greater risk for contrast sensitivity abnormalities than boys with normal hearing. The larger frequency of contrast sensitivity abnormalities in high spatial frequencies than in other frequencies may demonstrate greater defects in the central visual system compared with the periphery in individuals with hearing loss.