ABSTRACT. – We report here how the sensitivity of the eye of the cuttlefish (Sepia officinalis) to light changes with the growth of the animal. Measurements of body length and eye diameter show that cuttlefish hatch with relatively large eyes but these then grow throughout the animal’s lifetime at a slower rate than the body, resulting in an allometric scaling coefficient of less than one. Electroretinograms (ERG) evoked by the application of controlled flashes of light were obtained from different sized animals and demonstrated that ERG amplitude decreased with increasing animal size and this appears associated with a small decrease in retinal sensitivity. However, increasing the stimulus flash duration increased the sensitivity of the retina; this result is similar to the situation in vertebrates but not that in most other invertebrates. The cuttlefish retina was found to be 100 times more sensitive to flashes of blue light than yellow; however animals of 7 cm mantle length demonstrated an enhanced sensitivity to blue light, when compared to smaller or larger animals. The results are discussed in relation to differences in the lifestyles of the juvenile and adult animals, particularly the tendency for the young animals to live in bright, shallow waters, and the older animals to migrate to deeper, darker waters.