3.1.7: Assess the tear film

Question 1

What is a complete tear film essential for?

Answer 1

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

Question 2

What is dry eye?

Answer 2

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.

Question 3

Describe the outer oily lipid layer of the tear film?

Answer 3

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

Question 4

Describe the aqueous (watery large middle) layer?

Answer 4

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

Question 5

Describe the inner mucous layer?

Answer 5

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.

Question 6

What is the drainage pathway of the tears?

Answer 6

Through the puncta, through canaliculi, into lacrimal sac. Pumped into there from lid action and gravity feed to lower punctum.

Question 7

What are the symptoms of dry eye disease?

Answer 7

o Itchiness
o Irritation
o Increased Blinking
o Burning
o Grittiness
o Excess Watering
o Redness
o Blurred vision disappearing on blink

Question 8

What is evaporative dry eye (EDE)?

Answer 8

• 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)

Question 9

What is aqueous deficient dry eye (ADDE)?

Answer 9

• 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

Question 10

Describe the different parts of tear film assessment (H&S, secretion (volume), staining, stability (quality))?

Answer 10

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

Question 11

What are Lid Parallel Conjunctival Folds (LIPCOF)?

Answer 11

• 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)

Question 12

What is Lid Wiper Epitheliopathy?

Answer 12

• 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