Abstract
Purpose: :
To evaluate the through-focus quality of vision and subjective depth-of-focus (DoF) in patients wearing different multifocal contact lenses.
Methods: :
Subjective DoF is defined as the range of defocus leading to a defined level of blur (i.e. objectionable and bothersome blur). Through-focus subjective quality of vision was evaluated from -4 to 3 diopters (D) by 0.1-D step using a 5 items grading scale (i.e. ITU-R 500 recommendations) and DoF were measured using bothersome blur and objectionable blur criterias. All measurements were realized under cycloplegia (i.e. cyclopentolate 0,5%) using a 5mm artificial pupil and three 0,4 log MAR high contrast letters as a target in 5 conditions: naked eyed and eye wearing various contact lenses: Proclear multifocal (MF) Distance addition +2.50, Proclear MF Near addition +2.50, Air Optix MF High, Air Optix MF Low.
Results: :
The mean naked eye subjective DoF for bothersome and objectionable blur was respectively 1.18-D and 1.78-D. Using bothersome and objectionable blur criteria, the larger subjective DoF was obtained with the Proclear MF Near +2.50 (i.e. respectively 2.93-D and 3.62-D) and the Proclear MF Distance +2.50 (i.e. respectively 1,7-D and 3,05-D). However in these conditions, the through-focus curves and subjective DoF became bimodal leading to a lack of intermediate vision. Moreover, compare to the naked eye curve the width of the through-focus curves with contact lenses were enlarged at the expense of a decreased of the peak of the quality of vision. The width of the curve measured at an acceptable level of quality of vision (i.e. grade 2 on 5) and both subjective DoF were negatively correlated to the peak of the quality of vision (r2=0,86).
Conclusions: :
Multifocal contact lenses increased depth of focus. However there is always a tradeoff between depth of focus and quality of vision: the more depth of field is important, the more quality of vision degrades. Subjective DoF became bimodal only with some contact lenses, traducing differences between contact lenses geometry and subjectivity of multifocality.
Keywords: contact lens • presbyopia