3.1.7: Assess the tear film Flashcards
What is a complete tear film essential for?
o Antibacterial properties – to fight infection
o Transporting nutrients to cornea – cornea is avascular so needs nutrients from somewhere
o Optical performance of eye – if not good tear film then not smooth refraction of light into eye & so blurred vision is symptom of DE – if tear film is damaged then can affect vision overall
o Successful CL wear
o Removing FBs
* Dry eye is due to disorder or disturbance of tear film
What is dry eye?
A disorder/disturbance of the tear film due to tear deficiency or excessive evaporation, which causes
damage to the interpalpebral ocular surface and is associated with symptoms of ocular
discomfort.
Describe the outer oily lipid layer of the tear film?
o Produced by meibomian glands (if have MGD it is lipid layer you lack leading to ↑ evaporation)
o Smoothes tear surface and decreases evaporation
o Thin superficial oily surface layer
o Secreted by Zeiss, Moll and mebomian glands
o Prevents evaporation and spillage
o Consists of cholesterol esters, lecithin, fatty acids, free cholesterol and phospholipids
o 0.1- 0.2 microns thick
o Does not flow or enter conjunctival sac
Describe the aqueous (watery large middle) layer?
o Produced by lacrimal gland
o Carries nutrients & oxygen to cornea & carries away waste
o Hydrates cornea and prevents it drying out
o Washes away particles & irritants
o Central watery serous secretion
o Secreted by Krause and Wolfring glands
o 7 microns thick
o Basal tears constitute normal lacrimation
o Reflex or simulated tears result from lacrimal gland
Describe the inner mucous layer?
o Produced by conjunctiva (in particular goblet cells)
o Provides protection & ensures eye remains moist
o Vital for stability of tear film (vital in ensuring tear film remains on)
Now being described more as a mucin gradient through the tear film
o Secreted by conjunctival goblet cells, Manz glands and crypts of Henle
o Forms deepest tear layer
o Attracts aqueous
o 0.05 microns thick increases at lid margin
o Trap debris and epithelial cells, which are then removed through blinking.
o Also allows for tear stability and adheres to the epithelial corneal cells and conjunctival
goblet cells.
What is the drainage pathway of the tears?
Through the puncta, through canaliculi, into lacrimal sac. Pumped into there from lid action and gravity feed to lower punctum.
What are the symptoms of dry eye disease?
o Itchiness
o Irritation
o Increased Blinking
o Burning
o Grittiness
o Excess Watering
o Redness
o Blurred vision disappearing on blink
What is evaporative dry eye (EDE)?
- EDE is a consequence of increased evaporation of tears from the ocular surface, when the lacrimal gland is functioning normally
o Normal level of tears, they are just evaporating too quickly - This increase in tear evaporation leads to tear hyperosmolarity
- EDE can be due to either an abnormality with the ocular structures (intrinsic) or an external factor (extrinsic)
Intrinsic:
* Meibomian gland dysfunction
o Blockages in glands, don’t have lipid layer to protect aqueous which leads to increased evaporation
o Congenital lack, malformation or scarring of the meibomian glands
o Telangiectasia (see in pic) – classic sign of MGD – lots of BVs on inflamed lid
* Proptosis – thyroid eye disease lid retraction exposure of ocular surface leading to increased evaporation
* Low blink rate – commonly when looking at screens
Extrinsic:
* Contact lens wear – piece of plastic disrupting tear film
* Ocular surface disease e.g. allergy – look under eyelids to look for papillae
* Systemic drug use e.g. isotretinoin (Roaccutane – acne tx)
* Topical drug use – anything that’s preserved
* Vitamin A deficiency – may not be as common in UK
* Environment e.g. air conditioning, central heating (low humidity, dry atmosphere)
What is aqueous deficient dry eye (ADDE)?
- ADDE primarily refers to a failure of tear production by the lacrimal gland
- This leads to a reduction in the volume of tears which, in turn, causes hyperosmolarity of the tears due to evaporation
- This hyperosmolarity induces an inflammatory response on the ocular surface
- ADDE can be sub-divided into Sjögren’s syndrome dry eye and non-Sjögren’s syndrome dry eye
Describe the different parts of tear film assessment (H&S, secretion (volume), staining, stability (quality))?
o History and symptoms
➢ Dryness, Grittiness, Burning, Discomfort, Blurriness better on blinking
➢ Previous problems with contact lenses
o Secretion (Volume)
➢ Schirmer’s Strip – filter strip, hooked over lower lid, measures tear creep over 5mins, <10mm indicates DED, <5mm query Sjogren’s, >20mm normal)
➢ Phenol Red (cotton thread) test – impregnated thread, more reliable, <10mm diagnostic of dry eye, pH test in place for 15secs
➢ Tear Prism (Meniscus) – reservoir of tears, assess height centrally and peripherally, regularity, <0.2mm
diagnostic of dry eye
o Staining
➢ Sodum-flourescien – yellow dye which fluoresces green in UV light. It is a pH level indicator, intensity
increases in fluorescence in a more alkaline solution (peak around at pH 8.0). ‘Stains’ corneal epithelial cells by pooling in areas of dead or shedded cells. DE > 5 punctate spots
➢ Rose Bengal – stains dead and degenerated cells and mucus. Stings!
➢ Lisamine Green – stains membrane degenerated cells and mainly conjunctiva, only stains cornea in severe cases. Viewed in white light/red filter helps. DE > 9 punctate spots.
o Stability (Quality)
➢ Invasive break-up time (BUT) – hold eye open measuring time until break, blue light with fluorescein instilled, <10s indicates tear deficiency
➢ Non-invasive break up time (NIBUT) – specular reflection, B&L keratometry mires, tear scope, <15s indicates tear deficiency
What are Lid Parallel Conjunctival Folds (LIPCOF)?
- Approx. 0.1mm in width
- Combine nasal & temp for score
- Assessed without dye
- Should be there all time – not when nudge lids
LIPCOF degree 0 (no LIPCOF), 1 (1 permament & parallel fold), 2 (2 permanent & parallel folds), 3 (>2 permanent & parallel folds)
What is Lid Wiper Epitheliopathy?
- Alteration in epithelium of advancing lid margin due to friction during lid movement across the lens surface
- Tear film thickness insufficient to separate ocular surface and lid wiper
- Lissamine green staining easier to see this with – could use NaFl but harder
- Look for this when not seeing any other signs of DE on conj or cornea but px still really symptomatic – getting friction/discomfort on blink
Grading:
0: <2mm horizontal length of staining
1: 2-4mm horizontal length of staining
2: 5-9mm horizontal length of staining
3: >9mm horizontal length of staining
0: <25% average sagittal width of staining
1: 25-50% average sagittal width of staining
2: 50-75% average sagittal width of staining
3: >75% average sagittal width of staining
