In Chandogya upanidshad, In the the first adhyaya, the following passages dealing with the meditation of udgita, a hymn of samaveda covering the syllable Aum, refers to purusha who is seen within the sun and also within the eye with certain descriptions
Atha ya eso antaradtiye hiranmayah purusah drisyate hiranya………….tasya yatha kapyasam pundarikam akshini (Chandogya Upan. 1.6.6 and 1.6.7)
The Purusha referred in these passages denotes brahman. The supreme brahman having golden body implies the effulgent character of brahman. The red color of the eyes signifies the eyes similar to lotus petals ( Kapyasam pundarikam akshini).
1. Shankara in his commentary says this passages refer to the Saguna Brahman
2. According to Ramanuja the purusha is supreme person endowed with attributes and posses a spiritual body out of his own will.
3. According to Madhva, the purusha referred in these passages is supreme god, hari who posses blissful body and lotus like eyes.
The word Pundarikaksa (lotus eyed ) indicates the supreme purusa in the orb of Sun with lotus eyes.
The Taittiriya Upanishad says that the purusha in surya mandala is the same as the purusha in t he Hrdaya-Pundarika .i.e lotus heart. The Purusha in the sun prayed for daily by gayatri mantra is our in our lotus heart. Shankara suggests this by saying that the pundarikaksha is shining as Vasudeva in our lotus heart
So, Lord Vishnu who is identified as the supreme brahman is described in the Upanishads as having eyes like lotus petals . Hence, Lord Vishnu is known as Kamala Nayana.
Now let us see how Lord Vishnu is described as lotus eyed as per Vishnu sahsranama bhasya (commentry on Vishnu saharanama) by Adi Shankara and Sri Parasara Bhattar
Vishnu Sahasra Nama 40 : Pushkaraksah (Lotus eyed)
Parasara Bhattar provides the following meanings :
1. The lord with his lotus petals profusely rains grace on his devotees
and nourishes and develops their devotion.
2. The lord has lotus like eyes to enjoy fully the loveliness of
Goddess Lakshmi who also called Kamala.
3. As he resides in suryamandala, his two eyes appear like two
lotuses blossomed by the sunlight
Shankara says : Lotus eyed
Vishnu Sahasra Nama 111 : Pundarikaksah
Shankara gives the following meaning
1. He is seen and realized in lotus heart
2. He has lotus like eyes (Kamala nayana)
Parasara Bhattar gives the following meaning : He is the eye of all mukthas in the paramapada called pundarika
Vishnu Sahsranama Nama 615 : Swaksha
Shankara : Lord has two eyes resembling lovely lotuses.
Parasara Bhatta : The glance of eyes removes the miseries of devotees. Hence Lord is said to have eyes like lotus petals
All this clearly indicate Why Lord Vishnu is called Kamala Nayana or Pundarikaksha or Pushkaraksha or Swaksha, because Sruti says the supreme brahman of Vedas and vedanta, who is identified with Lord Vishnu has eyes like Lotus petals.
Therefore Lord Vishnu has epithets called Kamala nayana, Pundarikaksha, Pushkaraksha, Swaksha etc which means Supreme Lord with lotus like eyes (Kapyasam pundarikam akshini).