The sclera is the dense outer coating of the eye which provides the structural framework that defines the shape of the eye.It is mainly composed of collagen,elastin and interfibrillar proteoglycans.There is substantial evidence that profound biomechanical changes occur in the sclera with conditions such as myopia which are characterised by scleral weakening.Alongside biomechanical changes,a reduction of proteoglycans has been found in myopic eyes.However,to date few studies have been conducted to determine how proteoglycan content in the sclera affects its mechanical properties.In this study,in vitro degradation of proteoglycans in the porcine sclera was conducted in order to determine how this affects nano-scale changes in its structure and mechanical properties.Porcine scleras(n=21)were treated with α-amylase solutions(100%α-amylase,2mg/ml α-amylase in ultra clean distilled water,2mg/ml α-amylase in PBS.100%ultra clean distilled water and 100%PBS as control).The nano-topography and elastic modulus were measured before and after treatment by atomic force microscopy(AFM)using the Peakforce QNM modality.Proteoglycan content was analysed by dimethylmethylene blue assay before and after treatment.Results from this study demonstrated that proteoglycan content was reduced after α-amylase treatment(18.1%).The elastic modulus was reduced in all α-amylase depleted samples as compared to the control group(distilled water): 18.8%decrease after 2mg/ml α-amylase in ultra clean distilled water treatment(p<0.01),47.9%decrease after 2mg/ml α-amylase in PBS treatment(p<0.01)and 24.7%decrease after 100%α-amylase treatment(p<0.1).An increase in the elastic modulus(5%)was found in the group treated with 100%PBS buffer.These data demonstrate that proteoglycans play an important role in determining the nano-stiffness of sclera.Although α-amylase only partially depletes proteoglycans in the sclera,the elastic modulus decreased significantly with proteoglycan depletion.