ANATOMY AND PHYSIOLOGY

Lid has four layer: 1. skin 2. muscle 3. tarsal plate 4. conjunctiva. Skin of lid is very loose so any fluid or blood into it results in boggy edema of lid. It may be because of trauma or excessive watering. Skin is furthur divided into epidermis and dermis. Epidermis has keratin layer on top followed by granular layer, squamous cell layer and basal cell layer. Grey line is an anatomical and surgical mark dividing lid into two parts, the skin and muscle separated from tarsal plate and conjunctiva. The conjunctiva starts at the mucocutaneous junction behind meibomian glands at the lids. The eyelids contain both sebaceous and sweat glands. 

Question 1. what are the 4 layers of lid

answer. skin muscle  tarsal plate conjunctiva

Question 2: what is clinical significance of loose skin in lids

answer. fluid and blood can enter into it resulting in severe lid edema on even minor trauma

Lid skin subcutaneous tissue does not contain any fat. Lid muscle (orbicularis oculi) is supplied by 7th nerve and help closing the eye lid. Its antagonist muscle is levator palpebrae superioris (LPS ) is supplied by 3rd nerve and helps open the lid. LPS originate from the lessor wing of sphenoid. orbicularis oculi consists of two parts, the orbital and palpebral part. The palpebral part is furthur divided into pretarsal and preseptal parts.

Question: What is the nerve supply of lid

The tarsal plate is fibrous structure containing meibomian glands which are modified sebaceous glands, Upper tarsus is 10mm long while lower tarsus is 5mm long. There are 50 glands in upper tarsus and 25 glands in lower tarsus.

Question: which lid has more meibomian glands

The lids act as wipers of wind screen and spread tear film over external ocular surface, hence prevent its drying up. There reflex closure prevent any foreign body entering into eyes.

Question: What are two functions of eyelids