Ametropes with low levels of astigmatism (between −0,5 and −1,00 D) can be fitted with either spherical or toric contact lenses. Typically, aided visual acuity is used to determine if a spherical contact lens is adequate. However, visual acuity only measures vision in high contrast environments. Contrast sensitivity function is a measurement of a person’s ability to detect low contrast patterns and can be argued to give a better representation of the overall quality of vision. Surprisingly, there is a dearth of research comparing soft toric contact lenses with soft spherical contact lenses regarding contrast sensitivity performance.

The aim of this thesis was to compare visual acuity and mesopic contrast sensitivity with soft spherical and toric contact lenses on test subjects with between −0.50 and −1.00 of refractive astigmatism. The test subjects were all non-presbyopic and had less than ±3,00 diopters of spherical refractive error. The study was commissioned by Oulu University of Applied Sciences.

A total of eight test subjects were fitted with soft spherical and toric contact lenses, in random order. First, visual acuity with spectacles was measured with a logarithmic Snellen chart. After a proper contact lens fit was determined, the test subjects’ visual acuities with contact lenses were recorded and their contrast thresholds in photopic conditions were measured using the Pelli-Robson chart. Mesopic contrast sensitivity was evaluated separately for both the spherical and toric lenses in binocular conditions with and without glare by employing Rodenstock’s Nyktometer.

In four test subjects, binocular visual acuity improved with toric contact lenses. In two test subjects, visual acuities remained the same with both spherical and toric corrections. Furthermore, in two test subjects spherical contact lenses provided better visual acuity. Half of the test subjects had lower measured mesopic contrast sensitivities with toric contact lenses.

Any marked differences between soft spherical and toric contact lenses regarding mesopic contrast sensitivity could not be teased out in this study. The sample size employed in this thesis was small, only eight test subjects. Therefore, any meaningful extrapolations cannot be made regarding the results.