Ashtangahridayasamhita 91

91

sarva-thekṣeta nādityaṃ na bhāraṃ śirasā vahet |
nekṣeta pratataṃ sūkṣmaṃ dīptā-medhyā-priyāṇi ca || 39 ||

under no circumstances should one look directly at the sun, nor carry a load on the head; / one should not gaze steadily at minute, blazing, impure, or unpleasant objects;