The cubic kilometer is a metric unit of volume equal to 1,000,000,000 cubic meters. The symbol of the cubic kilometer is kmÂ³ . km3 = 1,000,000,000 m3 = 109 m3. To convert cubic kilometers to hmÂ³, damÂ³, mÂ³, dmÂ³, cmÂ³ and mmÂ³ , multiply by one followed by as many trios of zeros as there are places between the cubic kilometer and the other unit.
Rod photoreceptors are very sensitive to light and are responsible for night vision. These are the most abundant cell type in the human retina and are located closest to the back of the eye, near the retinal pigmented epithelium (RPE).
There are about six to seven million cones in a human eye and are most concentrated towards the macula. Commonly cited figure of six million in the human eye was found by Osterberg in 1935. Oyster's textbook (1999) cites work by Curcio et al. (1990) indicating an average close to 4.5 million cone cells and 90 million rod cells in the human retina.