anatomia dell'occhio	http://www.britannica.com/bcom/eb/article/1/0,5716,34071+1+33481,00.html
percezione visiva	http://www.britannica.com/bcom/eb/article/0/0,5716,60670+1+59186,00.html
prospettiva	http://www.britannica.com/bcom/eb/article/5/0,5716,60845+1+59357,00.html