Week 2.04 Dry Eye And Artificial Tears Flashcards
What are the functions of tear film
• Lubricate the globe
• Provide a smooth pre-corneal refracting surface
• Provides nutrients to cornea
• Removes debris from ocular surface
• Provide microbial defence
• Helps to regulate temperature of the globe
• Promotes wound healing
What antimicrobial abilities does the aqueous have
Lysosyme - enzyme that destroys bacterial cell wall
Immunoglobin - protein acting as an antibody
Beta-lysin - protein that destroys whole invading bacterial cell
Symptoms of dry eye
- Dry, gritty scratchy sandy feeling
- Tired eyes
- Pain/soreness
- Blurred vision
- CL intolerance
- Excessive tearing
Causes of dry eye
- Deficiency in tear volume
- Deficiency in tear quantity
- Abnormal eyelid function
- Systemic disease
- Environmental factions
- CL wear
- Medication
- Refractive surgery
Deficiency in tear volume
- insufficient secretion rate from lacrimal gland - tear drainage rate exceeds production rate
- leads to keratoconjunctivitis sicca
Main causes: - lacrimal gland
- reduced neural input to lacrimal gland
- poor tear retention due to eyelid abnormality or elevated evapouration rate
Major cause = reduced blink rate VDU
Deficiency in tear quality
- deficient lipid layer - MGD
- lipid contamination of mucin layer - migration of lipid to mucin layer
- contamination of the tear film by environmental factors
Abnormal eyelid function
Poor post blink redistribution of tear film
Poor tear pump mechanism - reduced efficiency of tear throughout on blink
Large palpebral aperture (ectropian) greater area exposed
Elevated tear secretion rate (ectropian) due to corneal irritation and reflex lacrimation - leads to epiphora
What is normal for TBUT
15-45 sec
Less than 10 seconds indicates unstable tear film
What is the schirmer test
- Schirmer I – strip placed into outer aspect of lower fornix, px can close eyes if more comfortable, time for 5 mins, measure wet area on strip
- Schirmer II – used less frequently, Schirmer I but with anaesthetic
10-15mm or more wetted in 5 mins is normal
<5mm is suggestive of dry eye
Phenol red thread test
Fold over 3mm of thread and hang inside lower eyelid - time 15 seconds then remove thread
Measure entire length that has turned red
Less than 10 - dry
10-20 = boderline dry
>20 = normal
Jones dye test
Useful in evaluation of epiphora
Test of lacrimal drainage
Procedure: px blows nose, instil fluorescein, wait 5 mins, blow nose again examine tissue
Irrigate fluorescein and blow nose then test other eye
Low viscosity aqueous solutions vs high
Short term retention in eye
Shorter term drug effect
Higher risk of systemic absorption
Good vision
Long term retention
Long term drug effect
Lower risk of systemic absorption
Poor vision
What are preservatives and what are commonly used ones
Protect opened preparation from bacterial colonisation
Benzalkonium chloride
Cetrimide viscotears
Chlorbutamol
Benzalkonium chloride
Concentrations: 0.01% and 0.004%
- 0.01% conc - destabilise tear film, weaken epithelial barrier, both not helpful for tear film as we want to stabilise it
Best avoided in px requiring long term therapy
Unpreserved options
Single use applicators - minims artificial
Unpreserved multidose
- stored refrigerated
- discard 1 week after opening
- modern preservative free systems can remain sterile for 12+ weeks
Aqueous artificial tears
Cellulose derivatives:
- Methylcellulose
- Carboxymethylcellulose
- Hydroxyethylcellulose
- Hypromellose
Carmellose sodium
Mucomimetic - mimics function of mucin
Preservative is puritite
Antibacterial, antiviral, anti fungal effects via protein synthesis inhibition
Hydroxyethylcellulose
Practitioners might use this to improve images on OCT scan
PVA
Polyvinyl alcohol based preparations
Another sub group of artificial tears
Does not blur vision
Does not mix well with other preparations
Reduces surface tension
Liposomes
Eye logic - brand name
Deficiency in lipid layer of tear film
Sprayed onto closed eyelid
Suitable for dry eye cont lens wearer
Systane
- mucomimetic
- gelling liquid (viscosity increases on contact with eye)
Systane balance - helps to restore lipid layer
Systane gel drops - thicker solution for use at night
Improvement of tear quality/consistency
- related to lipid layer deficiency
- aim to improve lipid secretion from meibomian glands
Hot compresses
Lid massages
Lid hygiene
Eye bad - heat in microwave, place over closed eyelid Suitable for 10 minutes, remove eye bag and massage eyelids
