• secretes water, electrolytes, & proteins
• part of functional unit that maintains tear film homeostasis
• meets tear fluid demand via neural & hormonal feedback loops

• Basal & reflex secretion from primary & accessory lacrimal glands
• normal secretion 1.2 μL/min
• secretion inc 100X w/ stimulation

• dec w/ age (50% by age 65)
• no daytime variation
• negligible during sleep
• newborns secrete w/n 24 hrs

What are the Accessory Lacrimal glands?

• Krauss (lateral fornix)
• Wolfing (upper margin of tarsal plate)

identical structure to lacrimal
responsible for <10% total aq. secretion

• mostly regulated via parasympathetic & sympathetic portion of reflex arc (afferent input is ocular surface stimulation)
• non-regulated constitutive or intrinsic: IgA

• 98.2% H₂O
• glucose
• urea

Describe the Afferent Lacrimal Reflex Arc:

Note-Stimulus to Secretion (reflex)

• stimulation of CN V : cornea, conjunctiva (foreign body, trauma, disease, etc.) & nasal mucosa
• other loops: Dazzle (CN II); taste (CN VII); cough/sneeze/laugh (CN IX & X); cortical input (emotion, pain)

True or False:

Tear production can increase or decreasue with the use of drugs.

TRUE.

EX: inc w/ marijuana, epinephrine, methacholine, etc &

      dec w/ atropine, nitrous oxide, diazepam, beta-block

Differentiate b/n Isosmolar, Hyperosmolar,

& Hypo-osmolar solutions:

Isosmolar = 290 mOsm

Hyperosmolar = >290 mOsm

Hypo-osmolar = <290 mOsm

Isotonic = soln w/ same solute concentration as cytosol

Hypertonic = soln w/ greater solute conc. than cytosol

Hypotonic = soln w/ less solute conc. than cytosol 

increased stimulation

(more fluid & less dissolved protein)

normal = 304-318 mOsm/L

serious dry eye = above 318 mOsm/L 

Evaporation

• anatomical, environmental, dec. tear turnover
• meibomian gland dysfunction = lipid deficiency

Reduced aq. production (secretion)

• reduced neural input (HSV, CL, LASIK, DM)
• inflammation
• hormonal, autoimmune disorder

• common canaliculus angles act as a valve (encircled by orbicularis muscle)
• eye lids also contribute

• 10-25% of secreted tear volume lost by evaporation 
• remainder drained into nasal passage
• some absorbed in nasolacrimal system

• toward puncta w/ blink
• along lacrimal river or tear meniscus/prism
• tears go into puncta
• puncta open only during eye-open phase

reflex tears are not part of tear film

interested in basal layer of tears that coat surface of eye

outer lipid layer

middle aqueous layer

mucous layer

• optical - smooths surface of cornea
• physical protection/buffer/lubricates
• flushing action/garbage pick-up
• bacteriostatic/lytic - lysozyme, betalysin, lactoferrin, IgG, IgA
• healing - WBC, Epidermal GF, TFG
• osmotic gradient - important for cornea
• nutrition

Exocrine - (lacrimal gland) release contents via duct to target

Endocrine - systemic (circulation) passage of hormone to target

Apocrine - like Goblet or Moll (sweat), apex of secretory cell released w/ secretion

Holocrine - like Zeiss or Meibomian (sebaceous), secretory cell enters duct w/ secretion then ruptures

1. Mucin - most posterior

2. Aqueous - middle layer

3. Lipid - anterior layer

• glycosylation of membrane bound proteins on surface of corneal epithelial cell
• microvilli inc. surface area
• interacts w/ mucin layer of tear film 

• plays a role in stabilization of tear film (disruption can lead to instability of tears & dry eye; contact lens can cause this)
• protects against bacterial pathogens; anti-bacterial; kills bacteria

• heterogenous collection of glycoproteins
• most internal layer closest to cornea  & made by goblet cell
• sugar side chain interacts w/ sugar chains of glycocalyx on apical surface of epithelium which provides tear film stability
• during sleep entrapped by caruncle cilia; known as "gradu" or "eye crud"

• provide hydrophilic surface
• lubrication
• healing
• protection from pathogens
• antioxidant

• ***Goblet cells in conjunctiva (unicellular apocrine gland)
• non-goblet epithelial cells like crypts of Henle (tarsal conjunctiva) or glands of Manz (limbus)

• Lacrimal gland
• Accessory lacrimal glands (glands of Krauss & Wolfring)
• Goblet cells
• Glands of Moll (sweat),Glands of Zeis (sebaceous), & Meibomian glands (sebaceous)

Lacrimal gland

Glands of Krauss & Wolfring (Accessory lacrimal glands)

Glands of Moll

Glands of Zeiss

Meibomian glands

Parasympathetic - Acetylcholine (ACh)

Sympathetic - Norepinephrine & neuropeptide Y (NPY)

Aqueous sources 

(Lacrimal gland is 90-95%, also accessory lacrimal & teritary in which some bulk flow from anterior chamber)

• delay evaporation of aqueous (by 90%)
• lubricate lid
• spreads w/ blink & carries aqueous
• dec. surface tension of tear film
• prevents overflow of tears @ lid margin
• disruption of lipid layer can lead to dry eye

neural: 

parasympathetic = Acetylcholine & Vasoactive    intestinal peptide

sympathetic = neuropeptide Y

hormonal: androgens

causes tear film disruption

inflammation of eye lids disrupts lipid layer of tear film b/c phospholipase enzyme (PLA₂) is secreted by inflammatory cells

tear break up time

interval from last complete blink to first random dry spot

• normal = 15-45 sec
• abnormal & clincally important = <10 sec 

(indicates there is too much evaporation and drying occuring in eye)

• wetting thin paper strip, one end placed in cul-de-sac of LL
• used to determine if there is proper aqueous secretion in the eye 
• normal >10 mm in 5 min
• with (basal) & without (reflec) anesthetic

• Sensitivity is 25% - miss many dry eyes
• Specificity is 90% - most caught are true dry eyes

• protein antibody rxn determines prescence of proteins on tear soaked filter paper
• lysozyme (quantiplate assay)
• lactoferrin (lactoplate assay) -  most widely used; can detect Keratoconjunctivitis sicca (KCS)

• Impression cytology (# & quality of goblet cells; cellulose acetate paper pressed against bulbar conjunctiva & observed microscopically)
• Periodic Acid Schiff (PAS; stains mucin containing goblets)
• Ferning (drying patterns on slide; observed by microscope, reflect tear compositions)

test in which the meibomian glands are presssed to assess meibomian gland production or dysfunction

used to test lipids

• slit lamp evaluation (tear film using specular reflection & tear meniscus)
• reflect grid pattern (placido disc) from cornea; waviness shows disruptions; dec TBUT
• tear scope

• corneal epithelium
• basement membrane
• Bowman's layer
• Stroma
• Descemet's membrane
• corneal endothelium

• avascular
• transparent
• major refractive surface of the eye

• barrier to invasion of pathogens, excess fluid uptake into stroma (dehydration/transparency), & free diffusion of molecules
• transmits O₂, CO₂, & metabolites
• provides compatible surface for tear film distribution (establishes glycocalyx)

the cornea is a UV filter and reflects 30-60% of overhead radiation; absorbs UVC (,310nm)

note: filter @ CERTAIN wavelength

doesn't express cytoskeletal structure of typical

refers to epithelium 

Basal cell: single layer

Wing cells: 1-3 layers

squamous (superficial) cells: 2-4 layers

• complete cycle 7-10 days to regenerate new epithelium 
• progresses from basal --> wing --> squamous (proliferation)

apoptosis (cell death/destruction)

begins during wing cell stage

• form seals of tissues & barriers for cells
• provide intercellular & cell-basement membrane anchorage
• mediate intercellular communication (Zonula occludens, desmosome, gap junctions)

• hold tissues together
• required for cell migration
• play a role in signal transduction
• hemidesmosome (half; one cell; b/n cell & EM)

• responsible for mitosis
• cell originate from stem cells @ limbal epithelium
• sole source of new cells w/n corneal epithelium
• secrete basement membrane 

it could divide by  mitosis --> change to a wing cell -->

change to a squamous cell --> become a unicellular layer

• formerly basal cells 
• different in shape & structure: no longer columns but like finger
• push toward outside but DO NOT divide; no cell division or mitosis
• interdigitation 

• formerly wing cells
• anteriorly; microvilli w/ adherent glycocalyx
• no cell division takes place
• apoptosis very prominent here

• Sodium Flurorescein (NaFL)
• Rose Bengal
• Lissamine Green

• yellow; used most often
• stains erosions/interruptions in the cornea
• detects ocular surface lesions & fills holes in cell
• will not penetrate intact cornea; wash out

• pink; stains degenerated/sick or dead cells
• particularly useful for dry eye diagnosis

• same purpose as rose bengal
• may be used when red eye from stain is of concern

•  secreted by basal cells
• collagen
• cell adhesion molecules (CAMs)

• not a true membrane; underneath basal membrane
• acellular, interweaving, non-parallel fibrils
• among mammals, only in primates
• function unknown

• 78% water
• rest is dry weight (15% collagen & 5% ECM)
• purpose of collagen is to support/maintain structure, wound repair, & anchoring device

• basic unit of collagen
• cross-linked array of staggered parallel molecules
• 67nm macro-periodic banding by alignment
• strength of tissue determined by this cross-linking

Differentiate the fibril of the cornea vs. sclera:

size & arrangement

• cornea: 30 nm diameter; forms parallel sheets
• sclera: 150 nm diameter; intervoven & variable size

spacing critical for transparency

•  42-44 nm b/n fibrils; cornea transparent
• variable; sclera white

collagen fibrils

• Proteoglycan - bound to GAG, disorders are Dystrophy
• Glycosaminoglycans (GAG) - sulfated

will see opacities all over cornea

• sulfated GAGs have strong (-) charge that attracts Na+ and pulls in H₂O
• stroma has greater affinity for H₂O than is optimal for transparency
• leads to accumulation of water/fluids

• basement membrane secreted by endothelium
• very elastic; hard to break, resistant to rupture

• amitotic uniform single layer
• permits passage of nutrients & metabolites
• maintains hydration of cornea via pumps
• secretes basement membrane (Descemet's)

• cornea is rich in sensory nerves
• innervated by ophthalmic division; V₁

• Descemet's membrane & endothelium are not innervated
• conjunctival plexus @ limbus feeds peripheral epi.
• long posterior ciliary nerve; 1st mm myelinated

• high density of nerves + lots of overlap = poor spatial location
• cornea one of most sensitive tissues of body; protective mechanism

nociceptors -

detect physical or chemical damage;  sensitive but can't distinguish; sensitive to mechanical pressure

• serve to maintain vitality of tissues (trophic)
• maintains dead tissue to keep it alive
• patients w/ sensory deprivation cannot feel or work problem area; leads to epithelial erosions/ulcers

• LASIK & other refractive surgeries
• contact lens use
• dec. from center to periphery & dec. superiorly
• dec. w/ less oxygen
• dec. w/ lower temp.
• dec. w/ age
• dec. in the morning (and inc. throughout day)

• corneal healing - cell migration
• intact epithelial innervation may be essential for normal metabolic levels to occur

• limbal vessels of minimal importance
• aqueous: glucose, a.a., nutrients, some oxygen
• tears: oxygen; atmosphere
• palpebral conjunctiva: oxygen, nutrition in closed eye

• simple diffusion from air; rate depends on gradient
• epithelium requires 10X stroma
• endothelium normally gets most from aqueous

• point at which swelling occurs
• approximately 50 mmHg
• COT crossed --> hypoxia = swelling
• oxygen tension higher when eye is open

• gradient very big; very important exit of CO₂; more CO₂ in eye than in atmosphere
• greater than O₂ due to low CO₂ atmospheric pressure

• need a lot of glucose to maintain paths, migration, etc.
• most comes from aqueous with help (aq. conc. greater than tears); also faciliated diffusion

aerobic --> pyruvate

anaerobic --> glycogen

• oxidation of glucose to either lactate (less O₂) or pyruvate (more O₂)
• 80% glucose metabolism

• w/ plenty of O2: pyruvate futher oxidized in Krebs/citric cycle (aerobic = 36 ATP)
• O2 deprived/hypoxic: lactate leads to epithelia & stroma edema (anaerobic = 2ATP)

• works at metabolic junction of aerobic & anaerobic metabolism; present in tears

• no ATP
• normal and hypoxic conditions
• dependent on NADP conc.
• generate NADPH necessary for synthesis of aromatic amino acids

• important in patients w/ diabetes & high blood sugar
• excess glucose
• adose reductase (AR)

• oxidative stress from free radicals (unpaired electron scavenged by antioxidants)
• first, Superoxide Dismutase transfer O₂ ---> H₂O₂
• next, Catalase & Glutathione Peroxidase (GPx) transfers H₂O₂ --> O₂

• O₂: air --> atmosphere
• Glucose: fuel --> aqueous or glycogen stored in epi.
• CO₂: exhaust --> metabolic by products

• spacing & arrangement of fibrils (keratocytes, proteoglycans, GAGs)
• not thickness dependent
• affected by water w/n proteoglycan matrix, heredity, injury & repair

• determined by how photons interact w/ electrons in atoms
• energy transfer must result in electrons reradiating as photons of same frequency & energy level
• direction of energy transfer must be maximally fwd
• constructive interference

constructive interference (wavefronts in-phase) in direction of transmission

destructive interference (out of phase) reduces fwd transmission

thicker cornea (due to edema) has reduced light transmission

Note: "thickness" not the determining factor

• diameter of fiber
• spacing (42-44 nm)
• arrangement

• stroma hydration inc. linearly w/ inc. corneal thickness
• stroma has natural tendency to imbibe water & to swell due to hydrophiilic nature of proteoglycans in ECM

• swelling pressure in normal corneas is about 55 mm Hg
• pressure is inversely related to corneal thickness
• EX: cornea of 150% normal thickness has swelling pressure of 15 mm Hg

• evaporation 2.5μL/cm²/hr
• evaporation responsible for 5% dec. in corneal thickness during day compared to immediately on awakening

1. Endothelial Barrier
2. Endothelial Pump

(barrier not as effect as epithelial barrier)

• w/ removal of endothelium: cornea swells 127μm/hr
• w/ removal metabolic pump: 33μm/hr

• represents movement of fluid & solutes from aqueous humor into stroma
• necessary to supply avascular cornea w/ nutrients, glucose, & amino acids

when the cornea is cooled, it swelled

when temp. returned to room temp., the cornea returns to normal thickness

dec. temp. = inc. thickness

inc. temp. = dec. thickness

• endothelial "pump" establishes gradient by transport of ions from stroma into aqueous, allowing water to flow
• Na+ is major driving force; maintains cornea in deturgescence state for corneal transparency

Na+/K+ ATPase is most studied

located in basolateral membrane of endothelial cell

• present in normal humans @ 1.5 x 10⁶ pump sites per cell
• inhibition of pump by ouabain blocks sodium transport which produces corneal swelling & prevents temp. reversal

• Na+ going toward aqueous
• K+ going toward stroma
• if inhibited, Na+ stays in stroma so thickness can't be changed & swelling results

• inherited disorders that may result of abnormal cellular metabolism
• usually bilateral, symmetrical, w/o inflammatory signs, & neovascularization

• basal cells are the only ones that can divide
• come from differentiated stem cells

• unlimited mitosis throughout life
• asymmetric cell division: 1 new cell remains stem cell; 1 new cell differentiates transit cell
• once committed to differentiation, can't reversed

1. inflammation
2. granular tissue forms: re-epithelialization
3. remodeled/new matrix formed
4. wound contraction
5. collagen accummulation; scar cells

• central defect: heal by migration of adj. epithelium
• peripheral defect & large defect: heals @ faster rate
• w/ complete loss of stem cell population: slow conjunctival cell 'trans-differentiation' similar corneal epithelium

• diabetes mellitus
• epi. basement membrane dystrophy
• alkali burns (damage to stem cells)
• mucin deficiency disorders
• tear film disorders
• eyelid disorders
• inflammation, atopic disease
• neurotrophic disease
• herpetic disease
• drug induced

• ulcer can result from any delayed healing
• balance of collagenase/matrix-metallo-proteinase (MMP) activity (cleaves collagen) & collagen synthesis

thin & transparent mucous membrane that lines the eyelids & is reflected @ the superior & inferior fornices onto the anterior suface of the eyeball

creates a potential space (conjunctival sac)

• allows independent movement of eyeball & eyelids
• protection of cornea from external environment
• contributes to tear film formation (mucous & aqueous layers)
• glycocalyx
• first line of defense against infections

• Palpebral conjunctiva: lines posterior (internal) surface of eyelid
• Conjunctival fornices: allow eyeball & eyelids to move independently
• Bulbar conjunctiva: covers anterior part of eyeball

Palpebral - marginal (mucocutaneous junction); tarsal;   orbital

Fornices - superior; inferior; lateral; medial (plica semilunaris & caruncle)

Bulbar - scleral; limbal

• orbital part is "b/n" tarsal conjunctiva & fornices
• orbital part contains more Goblet cells than tarsal region of conjunctiva
• contains Muller (or tarsal) muscle & acessory glands of Wolfring & Krauss

• nonkeratinized stratified squamous epithelium
• contains mucin secreting goblet cells overlying highly vascularized loose connective tissue layer (substantia propia)
• profusely innervated
• abundant lymphoid tissue

Which histological term defines the conjunctiva?

A. Amorphous membrane

B. Avascular connective tissue

C. Epidermis

D. Mucous membrane

• 4 fornices continuous w/ palpebral conjunctiva
• superior (largest), inferior, lateral, & medial
• function to ease stretching of conjunctiva on eye movements

• loosely attached to fascial expansions (connective tissue) of the EOM
• enables coordinated eyeball-eyelid movements

• levator palpebrae superioris & SR connect to superior fornix
• IR connects to inferior fornix
• LR connects to lateral fornix
• MR connects to deep tissue in plica semilunaris & caruncle (medial fornix)

scleral conjunctiva - has goblet cells

limbal conjunctiva - has Palisades of Vogt & lacks goblet cells

• in the limbal portion of bulbar conjunctiva
• structures around limbus radiating outward from cornea
• epithelial ridges covering underlying stromal condensations

• traps small forign objects & moves them away from cornea
• allows conjunctival blood vessels to nourish the periphery of the cornea
• niche for limbal stem cells

• inflammatory rxn of conjunctiva due to different factors (infections, allergies, irritants, etc.)
• accumulation of fluids in conjunctival connective tissue (chemosis)
• Dilatation of superficial blood vessels that will become more visible (conjunctival injection)

• after limbal stem cells' depletion
• corneal epithelium fails to regenerate
• corneal stroma gets covered by conjunctival tissue
• corneal neovascularization and opacification
• blindness

In which part of the conjunctiva are the goblet cells located?

A. Blood Vessels

B. Epithelium

C. Submucosa

• dense connective tissue that accounts for 5/6 fibrous tunic of eye
• sclera provides structure that protects intraocular structures, maintains shape & size of globe
• provides attachment for EOM

• thickest part near optic nerve; dec. gradually @ equator, reaches minimum below rectus muscle tendinous insertions
• thickness then inc. as it moves anteriorly towards area adj. to limbus

• thickest: in vicinity of optic nerve where it blends w/ dural sheath
• thinnest: beneath insertion of 4 rectus muscles

• sclera forms incomplete sphere (12 mm diameter)
• interrupted by 2 foramina, 1 anterior for cornea & 1 posterior for optic nerve & central retinal vessels

• anterior - cornea removed
• posterior - contains lamina cribrosa; passage for optic nerve axons & central retinal vessels

contains structures important in aqueous drainage

• trabecular meshwork
• canal of schlemm
• scleral spur

• weakest part of fibrous tunic of eye is lamina cribrosa
• optic nerve cupping in elevated intraocular pressure

Define Dacryoadenitis:

What are the two types?

inflammation of the lacrimal gland

either acute or chronic

• usually of viral, bacterial, or rarely parasitic etiology
• most cases associated w/ systemic infection
• typically seen in children & young adults

• more common than acute form
• usually due to inflammatory disorders like thyroid ophthalmopathy & Sjogren's syndrome
• also seen in syphilis & tuberculosis

Temporal upper eyelid swelling

•  acute: redness & pain w/ tearing & discharge; S-shaped deformity of lid; preauricular lymphadenopathy & fever
• chronic: occasional redness & discomfort

Enlarged lacrimal gland

• acute: may affect only palpebral lobe; may cause inferonasal globe displacement if orbital lobe is involved

• warm compression
• treat underlying condition

• acute or chronic infection of lacrimal sac
• bacterial etiology; secondary to conditions that cause lacrimal sac tear stasis & predispose to infection

• long, narrow nasolacrimal ducts
• strictures of lacrimal ducts
• lacrimal sac diverticulum
• nasal lacrimal duct obstruction
• inflammatory sinus & nasal problems

• pain, swelling, & redness over nasal portion of lower eyelid w/ tearing & crusting
• possible fever
• tenderness of lacrimal sac
• expression of discharge form punctum

• warm compresses
• systemic antibiotics - lacrimal sac contents can be aspirated w/ 18 gauge needle for culture & gram stain
• topical antibiotic (if conjunctiva exists)
• may require incision & drainage
• dacryocystorhinostomy by oculoplastic surgeon (after infection resolved)

• mucocele formation
• orbital cellulitis
• infectious keratitis

• inherited disorders
• progressive accumulation of deposits w/n stroma
• caused by genetic mutations that lead to abnormal proteins

• linear, radially oriented, branching refractile opacities
• located in anterior stroma
• amyloid deposits
• cause recurrent corneal erosions & dec. vision

• phototherapeutic keratectomy  (PTK)
• corneal transplantation (but can recur in graft)

• discrete, gray-white "crumb-like" opacities
• located in anterior to mid stroma
• hyaline depositis
• clear cornea b/n deposits & in periphery
• coalesce & progress deeper over time

• none initially
• decreased VA later
• recurrent corneal erosions (not as common as in lattice)

• phototherapeutic keratectomy  (PTK)
• corneal transplantation (but can recur in graft)

• least common, most severe
• gray-white stromal opacities involving whole cornea
• stromal haze b/n deposits
• mucopolysaccharide (glycosaminoglycan) deposits
• appear in 1st decade of life
• severe visual loss by 2nd/3rd decade of life due to diffuse corneal haze

• Phototherapeutic keratectomy (PTK) - but not as useful as in lattice or granular
• corneal transplantation - recurrance in grafts less common than in other two

inflammation of cornea

• exposure keratitis - corneal dryness secondary to incomplete lid closure
• photokeratitis - UV radiation exposure (snowblindness; welder's arc)
• allergic - vernal keratoconjunctivitis

• bacterial
• viral
• fungal
• parasitic

• inflammation of both the cornea & conjunctiva
• aka epidemic keratoconjunctivitis (EKC)

1. episclera
2. scleral stroma
3. lamina fusca

• protects intraocular contents
• together w/ IOP, preserves shape of eyeball
• provides rigid insertion for EOM

• adults: sclera dull white color
• children: sclera thinner, allowing pigment cells in underlying choroid to show through (bluish)
• elderly: yellowish color due to fatty deposits

• innermost layer of sclera
• separated from external surface of choroid by perichoriodal space
• weakly attached to choroid by fine collagen fivers
• contains thin, irregular layer of melanocytes (faint brown color)
• many grooves caused by passage of ciliary vessels & nerves

• dense fibrous tissue intermingled w/ fine elastic fibers
• irregular arrangement of collagen fibrils makes sclera opaque
• few flat elongated fibroblasts & occasional melanocyte found b/n collagen bundles

• outermost layer of sclera
• loose connective tissue; connected to Tenon's capusle by fine strands of tissue
• merges w/ underlying scleral stroma
• becomes progressively thinner toward back of eye
• rich blood supply anteriorly (episcleral plexus)

• formed by branches of anterior ciliary arteries
• extends from insertion of EOM to corneo-scleral junction

• pronounced vasodilation of episcleral plexus (especially in limbal area surrounding cornea)
• occurs in presence of inflammation of cornea, iris, & ciliary body

• sectoral (70%) or diffuse (30%) inflammation of episclera

• subconjunctival & conjunctival injection
• may be asymptomatic or mild discomfort/pain
• may have chemosis, episcleral nodules, anterior chamber cell/flare

• usually self-limiting, no treatment needed
• consider vasoconstrictor, mild topical steroid, or oral NSAID if severe
• recurrent in 67% cases

• inflammation of sclera: anterior (98%) or posterior (2%)
• may be diffuse (40%), nodular (44%), or necrotizing (14%)
• over 50% cases bilateral
• associated systemic disease in 50% cases

• pain
• photophobia
• swelling (chemosis & scleral edema)
• subconjunctival & conjunctival injection w/ violaceous hue
• normal or dec. VA
• globe tenderness to palpation
• may have scleral nodules, scleral thinning, anterior chamber cells/flare, corneal infiltrate or thinning

• collagen vascualar disease (30% cases): rheumatoid arthritis, lupus erythematosus, wegener's granulomatosis, etc.
• herpes zoster
• syphilis
• tuberculosis
• leprosy
• gout
• porphyria
• post-surgical
• idiopathic

• Scleritis - sclera has violaceous hue; no blanching when topical vasoconstrictors, like 2.5% phenylephrine, are instilled; more painful!
• Episcleritis - eye looks redder w/ violet tinge; blanching does occur when 2.5% phen. instilled

• receives sensory innervation from ciliary nerves (pierce sclera around optic nerve; many supply posterior sclera; 2 long ciliary supply anterior)
• inflammation causes dull, aching pain
• pain worse in scleritis w/ eye movement since EOM insert into sclera

• about 1 mm thick posteriorly
• thinning @ equator to 0.6 mm
• thinnest, 0.3 mm posterior to insertion of recti musc.
• 0.8 mm thick @ corneoscleral junction (aka limbus)
• optic nerve perforates sclera @ posterior scleral foramen