The purpose of our, real world study is to explore contrast sensitivity differences after changes in ambient light setting in patients with glaucoma compared with controls (patients with ocular hypertension). Participants will be asked to read a Pelli- Robson chart under photopic (bright light conditions) and mesopic (intermediate light conditions); followed by scotopic conditions (dim light conditions). This chart is a fast, easy, and effective way to measure spatial contrast sensitivity with reliable and reproducible results(60). This study will therefore help clinicians gain more insight into glaucoma related disability and provide a possible additional tool to visual field testing in patients with advanced glaucoma where VF testing may be hampered by floor effects.