The lens in the humaneye is a convex lens. An equivalent diagram of light leaving an object then passing through aconcave is included below for comparison..


**The lens is a transparent, convex lens in theeye that, along with the cornea, helps to refract light to be focused on the retina. Hence, Convex lens is present in human eye



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Concave Lens in Animal Eyes

Animals have evolved various adaptations in their eyes to suit their specific visual needs. While many animals have different types of lenses in their eyes, concave lenses are not commonly found in the animal kingdom. The primary reason for this is that concave lenses diverge light rays, making objects appear smaller and farther away. Most animals require the ability to focus on near objects and gather as much light as possible, which is not achieved efficiently with concave lenses. However, there are a few exceptions where animals possess concave lenses in their eyes.

1. Hagfish
Hagfish are marine creatures known for their unique eye structure. They have a single eye on each side of their head, and their lenses are concave-shaped. This adaptation allows hagfish to focus on objects at close range, helping them navigate and find food in their dark underwater environments.

2. Lamprey
Lampreys are primitive jawless fish with well-developed eyes. Their eyes also possess concave lenses, enabling them to focus on nearby objects and detect movements in their surroundings. This adaptation is particularly useful for lampreys during their larval stage when they live in freshwater habitats.

3. Some Deep-Sea Fish
Certain deep-sea fish, such as the tubular eyes of the barreleye fish, have partially concave lenses. These lenses aid in capturing and focusing light from bioluminescent organisms that are found in the depths of the ocean. The concave shape helps to enhance the fish's ability to detect small amounts of light and potential prey.

It is worth mentioning that while concave lenses are found in these animals, they are not the only type of lens present in their eyes. Most animals have a combination of lenses, including convex lenses, to achieve optimal vision for their specific ecological niche.

In conclusion, although concave lenses are not common in the animal kingdom, there are a few exceptions where animals possess concave lenses in their eyes. These adaptations allow them to focus on nearby objects, navigate in dark environments, and detect faint sources of light.