Cakkhu-pasāda; is eye. But eye in conventional sense is not cakkhuppasada. Cakkhu pasada is a rupa which is capable to receive the visual object. No other rupa can perceive visual object including mahabhuta rupa which is not cakkhu pasada. Cakkhu pasada cannot be seen by our eye and sensed by any of 5 physical senses. But it is a reality and it can only be sensed through manodvara. The same applies to other pasada rupa's.