Abbreviations

AAP American Academy of Pediatrics ACE angiotensin-converting enzyme AD autosomal dominant

ADHD attention deficit hyperactivity disorder AHP anomalous head position

AIDS acquired immune deficiency syndrome AKC atopic keratoconjun ctivitis

AOM acute otitis media

A-RS Axenfeld–Rieger syndrome AR autosomal recessive

AV arteriovenous

CA-MRSA community aquired methicillinresistant Staphylococcus aureus

CBS cystathionine beta synthase

CHED congenital hereditary endothelial dystrophy

CHRP congenital hypertrophy of the retinal pigment epithelium

CHSD congenital hereditary stromal dystrophy

CIN conjunctival intraepithelial neoplasia CNS central nervous system

CSNB congenital stationary night blindness CT computed tomography

CVI cortical visual impairment DNA deoxyribonucleic acid

DVD dissociated vertical deviation ECF-A eosinophil chemotactic factor of

anaphylaxis

EGA estimated gestational age

ELISA enzyme-linked immunosorbent assay EOG electro-oculography

ERG electroretinography ESRD end-stage renal disease

FNAB fine-needle aspiration biopsy GABA gamma aminobutyric acid GAG glycosaminoglycan

GPC giant papillary conjunctivitis GPI glycosylphosphatidyl inositol

HA-MRSA hospital acquired methicillinresistant Staphylococcus aureus

HBID hereditary benign intraepithelial dyskeratosis

HIV human immunodeficiency virus HSV herpes simplex virus

HZV herpes zoster virus

ICE iridocorneal endothelial (syndrome) ICP intracranial pressure

ICRB International Classification of Retinoblastoma

IGF-1 insulin-like growth factor 1 IOL intraocular lens

IOOA inferior oblique muscle overaction IOP intraocular pressure

IUGR intrauterine growth retardation JIA juvenile idiopathic arthritis

JRA juvenile rheumatoid arthritis LCA Leber’s congenital amaurosis MED monocular elevation deficiency

MIC minimum inhibitory concentration ML mucolipidosis

MMP matrix metalloproteinase MPS mucopolysaccharidosis MRI magnetic resonance imaging

MRNF myelinated retinal nerve fiber MRSA methicillin-resistant Staphylococcus

aureus

MSSA methicillin-sensitive Staphylococcus aureus

MTHFR methylene tetrahydrofolate reductase NF neurofibromatosis

NSAID nonsteroidal anti-inflammatory drug OCT optical coherence tomography

OI osteogenesis imperfecta

ONCCH oculoneurocutaneous cavernous hemangiomatosis

ONCS oculoneurocutaneous syndromes ONS organoid nevus syndrome

PAC perennial allergic conjunctivitis PAM primary acquired melanosis PCG primary congenital glaucoma PEVP pattern-evoked potential PFV persistant fetal vasculature

PHPV persistent hyperplastic primary vitreous PMMA polymethylmethacrylate

PPD purified protein derivative

PPMD posterior polymorphous membrane dystrophy

PSR proliferative retinopathy ROP retinopathy of prematurity RP retinitis pigmentosa

RPE retinal pigment epithelium SAC seasonal allergic conjunctivitis SLE systemic lupus erythematosus

SLRP small leucine-rich proteoglycan SW Sturge–Weber syndrome TORCHS toxoplasmosis, rubella,

cytomegalovirus, herpes simplex, and syphilis

TRIC trachoma inclusion conjunctivitis agent

Introduction

This chapter reviews the basic anatomy of the eye, with emphasis on any differences in the pediatric eye. In addition, attention is directed to the functional relevance of the anatomy. The areas covered will include the orbit and external eye, extraocular muscles, anterior segment, and posterior segment.

Orbit and external eye

Each orbit is a pear-shaped bony cavity that tapers posteriorly to form the optic canal. Its volume is approximately 30 mL and it measures approximately 40 mm in an adult.1 The presence of the globe or an implant is required to continue the bony expansion of the orbit in childhood. The bony orbit is composed of four walls: the roof (frontal bone and lesser wing of

the sphenoid), the lateral wall (zygomatic bone and greater wing of the sphenoid), the floor (maxillary, zygomatic, and the palatine bones), and the medial wall (ethmoid, lacrimal, maxillary, and sphenoid bones) (1). The thinnest walls of the orbit are the lamina papyracea in the ethmoid bone and the posterior—medial portion of the maxillary bone in the floor. With blunt trauma, these bones easily break allowing for decompression of the globe rather than rupture.

The eyelids provide the external covering for the globe. They contain a dense, fibrous tissue called the tarsus that provides the rigidity of the lids. The orbicularis oculi muscle innervated by the facial nerve allows eyelid closure. The levator palpebrae supplied by cranial nerve III, along with Mueller’s muscle innervated by the sympathetic system, opens the eyelids. The levator palpebrae inserts on the anterior surface of the tarsal plate, making the eyelid crease in

the upper lid. Congenital fibrosis of the levator palpebrae results in congenital ptosis. Meibomian glands are located in the eyelid and produce the oily layer in the tear film. Blockage of these openings results in formation of a chalazion. Finally, the orbital septum is connective tissue that forms a barrier between the anterior orbital structures such as the skin, and the deeper orbital structures. The septum attaches to the orbital rim, the levator aponeurosis, and the lower lid retractors. Penetration of the septum by infection differentiates preseptal cellulitis (anterior to the septum) from orbital cellulitis.

The lacrimal system is responsible for maintaining the moisture of the external eye. Tears play a vital role in the health and protection of the cornea and conjunctiva. The tear film consists of three layers: an outer lipid layer, a middle aqueous layer, and an inner mucus layer. The meibomian glands secrete the

oily layer as previous discussed. The lacrimal gland and the accessory lacrimal glands secrete the middle aqueous layer. The lacrimal gland is located in the superotemporal quadrant of the orbit in the lacrimal gland fossa of the frontal bone.2 The gland is divided into two parts by the aponeurosis of the levator palpebrae muscle: a larger orbital portion and a palpebral portion. The secretory ducts of the lacrimal gland empty into the superior cul-de-sac approximately 5 mm above the tarsal border. All ducts pass through the palpebral lobe. Damage to the palpebral portion will significantly impact on the secretory function. The facial nerve supplies the lacrimal gland. In addition, the accessory lacrimal glands of Krause and Wolfring are located within the superior cul-de-sac (2).

The drainage system for the tears begins with the eyelids pumping the tears towards the puncta which are small outpouchings located 6 mm from the medial angle of the eyelids