The Eyes

Describe the eyelids

• thin curtains of skin, muscle, fibrous tissue and mucus membrane

What are the 2 main roles of the eyelids and how do they achieve this

• protection from injury and excessive light

  • physical screening

  • reflex blinking in response to various stimuli e.g. approaching objects, bright lights, stimulus tactile

• production and distribution of tears

  • spontaneous blinking

What are the meibomian glands

• modified sebaceous glands

• located in tarsal plates

• secrete outer lipid layer of precorneal tear film

What are the glands of Zeis

• modified sebaceous glands

• located on margin of eyelid

• produce oily substance that lubricates hair follicle of eyelash

What are the glands of Moll and their secretions

• modified sweat glands

• located on lid margin

• ducts open to eyelash or gap between them

• secretions:

  • bacteriolytic enzyme lysozyme, mucin 1, the immunoglobulin A → immune response

What are the functions of the tear film

• Maintain optically uniform corneal surface

• Flush cellular debris and foreign material from the corneal and conjunctival sac

• Lubricate corneal and conjunctival surfaces

• Provide oxygen and nutrients to the cornea

• Provide antibacterial protection

What can deficiency or malfunction of the 3 components of the tear film cause

• dry eye symptom

What are the puncta lacrimalia and where are they located

• small openings near upper and lower eyelid margins

• drain tears into the canaliculi

What role does capillary attraction play in tear drainage

• pull tears from eye into lacrimal ducts/sac

How do tears flow down naso-lacrimal duct and what prevent the reflux of tears

• by gravity

• w/ help from pumping action of blinking

• internal value system prevent reflux → keeps tear flowing in 1 direction

What happens if obstruction in tear drainage system

• dry or watery eyes

• bc improper tear flow

Describe the conjunctiva and the 2 types

• thin transparent mucous membrane covering the front portion of the eye

• bulbar lines globe

• palperbral lines posterior eyelids

• conjunctival fornix is where both types meet

• contains goblet cells that produce mucoid layer of tear film

How can the conjunctiva produce red eye

• vessels rapidly dilate w/ irritation or inflammation

What is the sclera and where is it located

• whites of the eye → tough opaque

• located beneath conjunctiva blending w/ cornea at limbus

• made of collagen ensures rigidity of eye → essential for normal optical function

How does the sclera repair itself

• avascular so repair depends on BV from surrounding tissues LIKE choroid (internal) and conjunctiva (external)

What do the cornea and sclera form together

• spherical shell → makes up outer wall of eyeball

Describe the episclera and disease

• thin membrane that lies between conjunctiva and the sclera

• may become inflamed → red eye

• pain is absent or dull ache

What is the cornea and its function

• curved transparent, avascular window of eye

• multi-layered epithelium, stroma of collagen and ECM, inner monolayer of endothelial cells

• allows rays to enter

• becomes focused on retina → essential for vision

• kept healthy by tears

How does the cornea receive O2 and nutrients

• from limbal BV, tears and aq humour

Why is the cornea highly sensitive to touch

• bc of nerve fibres from ophthalmic division of trigeminal nerve

• cause intense pain when epithelium damaged → cause infection, inflammation, pain, photophobia, may cause corneal ulcers

What is the anterior chamber and function

• behind cornea

• contains crystal clear fluid called aqueous humour

• maintain intraocular pressure so cornea retains optically useful shape

• nourish the lens and cornea

How is the aqueous humour formed

• active process by ciliary body

• filtered into posterior chamber

• fluid travel past iris into anterior chamber

What is conventional drainage in terms of aqueous humour

• fluid continually drains away from anterior chamber at canal of Schlemm in angle between cornea and iris

• fluid into trabecular meshwork and episcleral veins

What is unconventional drainage in term of aqueous humour

• drainage via uveoscleral pathway

How does chronic open angle glaucoma form

• trabecular meshwork undergoes morphological changes

• causes imbalance between production of aqueous humour and drainage

• causes gradual rise in intra ocular pressure so progressive damage to nerve fibres in the optic nerve head

Explain the changes in the pupil when intensity of light changes

• dark

  • pupil dilates bc radial smooth muscle fibres contract aka dilator pupillae muscles → innervated by SNS

• light

  • constrictions bc sphincter pupillae muscles contract → innervated by PSNS

Structure of the iris

• connective tissue

• w/ smooth muscle fibres BV and pigment cells

What does the iris control and how

• amount of light into eyes

• expand or contract causing pupil to dilate (mydriasis) or constrict (miosis)

What is the uvea

• iris, posterior choroid and ciliary body

Function of the ciliary body and structure

• formation of aqueous humour

• anchors lens in place

• contains muscles

• innervated by PSNS

What is accomodation

• when ciliary muscles adjust refractive capacity of lens for varying distance of visions

• contraction of muscles reduce tension on zonules that holds lens in place so lens becomes more convex

• relaxation increases tension on zonules so lens = flat

What is the lens

• transparent refractive area of eye

• responsible for fine focussing of light onto retina

• opaque lens = cataract (34% protein, 65% water)

What is vitreous humour

• thick clear gel

• made up of collagen and hyaluronic acid

• connective tissue that keeps eye shape

What is the retina

• light sensitive layer

• contains photoreceptor cells

• rods = night vision

• cones = colour and daytime vision

What are the effects of ageing on the eye

• lens looses elasticity, accommodation fails, point of vision moves further away aka presbyopia

• cataracts → lens fibres become opaque so eye looks cloudy

What is the most common cause of red eye

• inflammation of conjunctiva

• irritants, infective agents and allergen can cause

• main symptoms: redness, discharge, pain

How to distinguish from a serious infection to a minor ailment in the eye

• minor ailment typically affects both eyes, associated w/ discharge/itching/grittiness, pupil is normal and vision unaffected

How can a pharmacist check visual acuity

• ask patient to read small print w/ affected eye whilst other eye is covered

When should you refer in regards to pain

• actual pain (not irritation or discomfort) and visual disturbance

How to do physical examination of patient’s eye

• look straight ahead to look at pupil, cornea and sclera

• gently pull down lower lid and get Pt to look up so conjunctive viewed

Subjective history of symptoms - the perfect assessment helps check medical options

• Time of Onset

• Previous episodes

• Associated symptoms e.g. nature of discharge, discomfort, pain. Itching, photophobia, visual changes, haloes, loss of vision, URTI symptoms

• History of atopy/allergy

• Contact with individuals with similar problems

• Medication – ocular

Objective history of symptoms - uniquely colourful pupils rule!

• Unilateral or bilateral

• Cornea – is it bright or cloudy

• pupil size and shape. Pupils should be circular, central and equal in size – look for irregularity and inequality in size

• Pattern of redness i.e. is it generalised, localised or circumcorneal

What are the 5 P’s in relation to red flags w/ the eye

• pain

• photophobia

  • feeling of discomfort looking at light source

  • usually unilateral

• poor vision

  • if discharge in minor ailment usually cleared by blinking a few times, if pus etc would not be cleared easily

• pus

  • sign of infection WITHIN eye

• pupil abnormality

  • should be equal in size, central and circular in shape - any diff should be referred

What is a hypopyon

• pus accumulating in bottom of anterior chamber

Other referral criteria

• trauma to eye

When is topical delivery used for eyes

• common route of delivery

• when site of action is anterior segment of eye like glaucoma, conjunctivitis and keratitis, and infections

Disadvantages of topical RoA

• poor manual dexterity in elderly/disabled

• risk of stinging/burning

• Vitreous penetration is generally poor

• potential for contamination

• Preservatives are usually necessary can cause allergic or toxic reactions

• incompatible with contact lens wearers

• Systemic absorption and adverse effects possible

What is the main route for drug to reach anterior chamber of eye and what types of drugs can penetrate

• through cornea

• fat soluble → corneal epithelium

• water soluble → corneal stroma

• best if drug is both

Give an example of a pro-drug used in ophthalmic treatments

• Dipivefrine

• a pro-drug of adrenaline

How can ocular bioavailability be decreased

• drug bind to tear proteins

• breakdown enzymes in eye

What are the common excipients used in eye drop formulations and optimal pH

• Viscosity enhancers

• tonicity agents

• buffering agents

• preservatives

• 6.5-7.6

Why is particle size in ocular suspensions kept under 10 microns

• larger particles may cause gritty sensation and promote tearing

advantage of using high molecular weight polymers in eye gels

• increase viscosity

• promote retention

  • allowing for longer-lasting drug effects

Why opthalmic ointments often used at night

• cause blurring

• longer residence times

What should formulators avoid in ointments to prevent intraocular toxicity

• bases like lanolin, petroleum, vegetable oils