Astanga Hrudaya
स्वप्नेन रत्रौ कालस्य सौ म्यत्वेन च तर्पिता। शीतसात्म्या दृगाग्नेयी स्थिरतां लभते पुनः॥१९॥
Importance of Night and Sleep for Healthy Eyes. The eye is Agneyi – predominant with the fire element, being habituated to cold comforts it regains its strength after good sleep and nourished by the coolant nature of the night.
english translation