The Ocular Adnexa, Eyelids, Lid Margins, And Palpeblar Fissures
Forensic comparison microscopes can be used by a detective, research scientist, chemist, or a forensic scientist. Forensic comparison microscopes are able to compare two samples at the same time. Forensic comparison microscopes can also be used to view a suspect or victim’s eye anatomy like their ocular adnexa, eyelids, lid margins, and palpeblar fissures.
THE OCULAR ADNEXA
1. Eyebrows
The eyebrows are folds of thickened skin covered with hair. Underlying muscle fibers supports the skin fold. The glabella is the hairless prominence between the eyebrows.
2. Eyelids
The upper and lower eyelids (palpebrae) are modified folds of skin that can close to protect the anterior eye¬ball. Blinking helps spread the tear film, which protects the cornea and conjunctiva from dehy¬dration. The upper lid ends at the eyebrows; the lower lid merges into the cheek.
The eyelids consist of five principal planes of tissues, as seen using a microscope. From superficial to deep, they are the skin layer, a layer of striated muscle (orbicularis oculi), areolar tissue, fi¬brous tissue (tarsal plates), and a layer of mucous mem¬brane (palpebral conjunctiva). All these layers can be further studied using a microscope like a forensic comparison microscope.
Structures of the Eyelids
A. SKIN LAYER
The skin of the eyelids differs from skin on most other areas of the body in that it is thin, loose, and elastic and possesses few hair follicles and no subcutaneous fat, as seen in a microscope.
B. ORBICULARIS OCULI MUSCLE
The function of the orbicularis oculi muscle is to close the lids. When examined under a microscope, its muscle fibers surround the palpebral fissure in concentric fashion and spread for a short distance around the orbital margin. Some fibers run onto the cheek and the forehead. The portion of the muscle that is in the lids is known as its pretarsal portion; the por¬tion over the orbital septum is the preseptal portion. The segment outside the lid is called the orbital por¬tion. The orbicularis oculi is supplied by the facial nerve.
C. AREOLAR TISSUE
The submuscular areolar tissue that lies deep to the or¬bicularis oculi muscle communicates with the sub¬aponeurotic layer of the scalp.
D. TARSAL PLATES
The main supporting structure of the eyelids is a dense fibrous tissue layer that-along with a small amount of elastic tissue-is called the tarsal plate. The lateral and medial angles and extensions of the tarsal plates, when viewed under a microscope, are at¬tached to the orbital margin by the lateral and medial palpebral ligaments. The upper and lower tarsal plates are also attached by a condensed, thin fascia to the upper and lower orbital margins. This thin fascia forms the orbital septum.
E. PALPEBRAL CONJUNCTIVA
A layer of mucous membrane, the palpebral conjunctiva, which adheres firmly to the tarsal plates, lines the lids posteriorly. A surgical incision through the gray line of the lid margin splits the lid into an anterior lamella of skin and orbicularis muscle and a posterior lamella of tarsal plate and palpebral conjunctiva.
Lid Margins
The free lid margin, when examined under a microscope, is 25-30 mm long and about 2 mm wide. The gray line (mucocutaneous junction) divides it into anterior and posterior margins.
A. ANTERIOR MARGIN
1. Eyelashes-The eyelashes project from the margins of the eyelids and are arranged irregularly. The upper lashes are longer and more numerous than the lower lashes and turn upward; the lower lashes turn down¬ward. Eyelashes can be used to connect or relate crime scenes when these are compared and differentiated using forensic comparison microscopes.
2. Glands of Zeis-These are small-modified seba¬ceous glands that open into the hair follicles at the base of the eyelashes.
3. Glands of Moll-These are modified sweat glands that open in a row near the base of the eyelashes.
B. POSTERIOR MARGIN
The posterior lid margin is in close contact with the globe, and along this margin are the small orifices of the modified sebaceous glands (meibomian, or tarsal, glands).
C. LACRIMAL PUNCTUM
At the medial end of the posterior margin of the lid, a small elevation with a central small opening can be seen on the upper and lower lids. The puncta serve to carry the tears down through the corresponding canaliculus to the lacrimal sac.
Palpebral Fissure
The palpebral fissure is the elliptic space between the two open lids. The fissure terminates at the medial and lateral canthi. The lateral canthus is about 0.5 cm from the lateral orbital rim and forms an acute angle when viewed using a specialized eye microscope. The medial canthus is more elliptic than the lateral canthus and surrounds the lacrimal lake.
Two structures are identified in the lacrimal lake using a microscope: the lacrimal caruncle, a yellowish elevation of modi¬fied skin containing large modified sweat glands and se¬baceous glands that open into follicles which contain fine hair; and the plica semilunaris, a ves¬tigial remnant of the third eyelid of lower animal species.
In Orientals, a skin fold known as epicanthus passes from the medial termination of the upper lid to the me¬dial termination of the lower lid, hiding the caruncle. Epicanthus may be present normally in young infants of all races and disappears with development of the nasal bridge but persists throughout life in Orientals.
