Used for hunting on land, for communication and for detecting danger. Otterine sense of smell is likely to be similar in sensitivity to dogs.
Otters have small eyes and are probably short-sighted on land. But they do have the ability to modify the shape of the lens in the eye to make it more spherical, and hence overcome the refraction of water. In clear water and good light, otters can hunt fish by sight.
The otter's eyes and nostrils are placed high on its head so that it can see and breathe even when the rest of the body is submerged.
Long whiskers (vibrissae) growing around the muzzle are used to detect the presence of fish. They detect regular vibrations caused by the beat of the fish's tail as it swims away. This allows otters to hunt even in very murky water.
Physically, otter ears are tiny for streamlining, but they still have very sensitive hearing. However, while water transmits sound better than air, it is almost impossible to determine which way the sounds are coming from. Dolphins have special modification to their ears to overcome this problem, but otters don't so it is unlikely that otters use their hearing to hunt prey. Otter ears are protected by valves which close them against water pressure.