Here you go, this lot should keep you going for a while.

https://www.google.com/url?q=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC510520/pdf/brjopthal00688-0001.pdf&sa=U&ved=0ahUKEwidr7Dor-HUAhWFn5QKHSPKCbQQFggVMAg&client=internal-uds-cse&usg=AFQjCNGYDblGKfsqcJSPrbXZifQfEBefIg

https://www.google.com/url?q=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4824881/&sa=U&ved=0ahUKEwidr7Dor-HUAhWFn5QKHSPKCbQQFggPMAU&client=internal-uds-cse&usg=AFQjCNFcV7QUwNMcqLcPKchysazykdtDKA

https://www.google.com/url?q=https://www.ncbi.nlm.nih.gov/pubmed/9222228&sa=U&ved=0ahUKEwidr7Dor-HUAhWFn5QKHSPKCbQQFggXMAk&client=internal-uds-cse&usg=AFQjCNE1r0DWsGr22VJeprOiQ7hvIhcKbg

https://www.google.com/url?q=https://www.ncbi.nlm.nih.gov/pubmed/8266635&sa=U&ved=0ahUKEwiV0a3bsOHUAhUEE7wKHY31Bek4ChAWCAswAw&client=internal-uds-cse&usg=AFQjCNE6Dc8TAfLS8rlwcHUGrtOUpUYXFw

https://www.google.com/url?q=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4849103/&sa=U&ved=0ahUKEwiOq_WVseHUAhVIabwKHR8ICFw4HhAWCBowCQ&client=internal-uds-cse&usg=AFQjCNEKycb9k3nWaZrEne6P8kcIPnC1Eg