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Opthalmology > The Opaque Eye 1 > Flashcards

The Opaque Eye 1 Flashcards

1
Q

Layers of the corneal epithelium

A
  1. Basal Cells
    - Stems cells at the limbus (should persist forever) -> TransientAmplifyingCells capable of mitosis -> Basal cells -> differentiate to other layers
  2. Wing cells
    - no longer mitotic
    - 2-4 layers
  3. Squamous, non-keratinised epithelium
    - slough off with blinking (weekly)
    - replenished from below
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2
Q

What is necessary for permenant adhesions and healing to form?

A
  • Basal lamina
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3
Q

What 2 ways does epithelium heal? How does new epithelium move? What effects may this have?

A

> sliding
- with abrasion of superficial epithelial lesion that does not reach basal lamina
- ~ 1mm/day
- dependant on corneal health (eg. KCS) limbal basal stem cell population, basal lamina, species and age.
- limbal stem cells act as barrier to conjunctival overgrowth and conjunctivalization
vertical movement
- first epithelial sliding then basal cell mitosis
- takes 1 week/cycle
- regains thickness
centripetal movement from limbus -> center, every layer moves like this
- happens more quickly if basal lamina present
- chronic corneal disease or irritation may drag pigment in from limbus -> blindness
- esp pugs and GSDs (pigmented limbus)

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4
Q

When may superficial pigment deposition occour?

A
  • theory: irritants activate melanin production
  • at limbus and paralimbal conjunctiva
  • pigment deposited in new migrating epithelial cells -> central migration and in superficial stroma
  • can be severe esp in pugs
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5
Q

Is the cornea vascular?

A

NO not if healthy (exception: manitees, rocky mountain goat)
- with epithelial wound healing neovascularisation can occour
- inflammation stimulus
- vessels can coalesce -> granulation tissue
- atrophy over time once stimuls removed
> VASCULARISATION IS A MARKER OF CHRONICITY
- Budding takes 2-4d
+ 1mm/2days

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6
Q

How may vascularisation of the cornea assist healing and your dx?

A
  • superficial or deep (stromal)
  • highlights area of damage
  • stabilizing serum (ANTI - MMP and serum proteases, which unopposed can -> corneal melting [produced by bacteria, neutrophils and other cells])
  • neutrients, growth factors, inflame cells
  • structural support
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7
Q

What is the stroma made up of?

A

> collagen lamellae
- type 1 collagen fibrils (+ others)
- fibrils travel limbus to limbus
- united and ordered by GAGs (chondriotan, dermatan sulphate)
- dehydration/deturgenscence
- transparency
keratocytes
- relatively inactive fibrocytes
- low numbers for transparency
- contribute to lamellar creation and maintainance
- differentiate into fibroblasts and myofibroblasts (myofibrocytes with pseudopodia and a-sm-actin for cell movement)
chemical factors
- IL-1, EDGF, EGF, TNFa, TGFb, collagenases, metaloproteases etc.
- produced by corneal nn. and other cells (lacrimal glands, epithelium, keratocytes, leucocytes, BACTERA)

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8
Q

Which cells are involved in stromal healing? What is required for proper healing?

A

> cellular attraction - destruction and clean up
- monocytes and macrophages, neutrophils and leucocytes
keratocyte-mediated build up
- collagen fibrils
- ECM GAGs
- initially GAGs incorrect type and haphazardly laid down -> scar
BALANCE between these required for controlled healing

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9
Q

How quickly does stromal regeneration occour cf. epithelial? What stage follows reconstruction?

A

Slower

  • remodelling follows reconstruction
  • all transparency will eventually be regained (mostly)
  • cats better at remodelling than dogs.
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10
Q

What is the first GAG to form?

A

Hyaluronic acid

- then others increase [] with time

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11
Q

What may occour during stromal regeneration?

A

Epithelium tries to ‘help’

  • epithelial hyperplasia -> facet formation (flat edges to cornea)
  • may remain for life
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12
Q

How is the endothelium layer arranged? Properties?

A
  • one cell thick
  • honeycomb appearance hexagonal cells
  • v. sensitive (lens luxation touching endothelium -> destruction)
  • NON REGENERATIVE
  • actively pumps water out of cornea
  • preserves fibre alignment and helps transparency
  • strong intercellular junctions (as in epithelium) = natural barrier between cells
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13
Q

How can the endothelium repair? What can occour is this capacity is surpassed?

A
  • Not regenerative
  • 50% cells lost in adulthood
  • cells grow when neighbouring cells die (polimegathism)
  • lose hexagonal shape (pleo/policorphism)
  • ^ no NaK pumps
  • POINT OF DECOMPENSATION*
  • > corneal oedema will occour after this point
  • point of decomp varies 800-500c/mm2 in dogs
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14
Q

Causes of endothelial damage

A
  • glaucoma, uveitis
  • anterior lens luxation (contact w/ anterior lens belly)
  • firect damage intraoperatively (instruments)
  • chemical damge (injected into eye)
    > PRIMARY endothelial degeneration (blisters of fluid in cornea, ulceration, common in ‘hunting breeds’ but not v common overall)
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15
Q

What 2 factors influence self repair?

A
  1. superficial v deep
  2. does the tissue know its ulceratied?
    - cell cell communication
    - corneal sensation (desensitisation, brachycephalic factor)
    > affects keratocyte activation and production of tissue factors
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16
Q

How quickly does re-epithelialisation and stromal reconstruction occour?

A

> re-epithelialisation fast providing stroma is healthy
- re-anchoring to secrure the epithelium takes MONTHS
stromal regeneration starts immediately but takes longer to complete
- if unstable can -> melting (collagenolysis) d/t chronic inflame/irritation or 2* infection
- once melting starts, v hard to control

17
Q

How soon after being presented with a superficial ulcer should you re-see an animal?

A

~3d - expect 3mm decrease in size

- if no improvement or worse, what is causing the imblanace?

18
Q

What are the most common causes of non-healing ulcers?

A 
2* 
> tear film problem (quantitative or qualitative) 
> eyelids, TE
> repair process (brachycephalic factor, 2* infection, melting) 
1* [VERY RARE]
> SCCEDs
> calcium deposits
> FHV-1: 1* infection -> ulcerative dz
19
Q

What 2 main thoughts should cross your mind if ulcer is taking too long to heal?

A
  1. what caused the ulcer in the 1st place - what am I missing?
  2. changing topical antibiotics is not the answer!!
20
Q

oUTLINE DIAGNOSTIC TESTS USEFUL FOR CORNEAL ULCERATIVE DISEASE

A
  • STT1
  • eyelid exam
  • eyelid function/structure
  • cytology? (often not helpful, but can distinguish rods v cones)
  • additional factors ( brachycephalic etc.)
21
Q

What medical tx options are available?

A
  • protect from self trauma (collar, tarsorrhaphy horizontal mattress suture with stents, TE flap [but not that great - no benefit over bandage lens and tarsorrhaphy, damages conjunctiva, prevents exit of debris and evaluatin of eye])
  • Abx for PREVENTION
  • atropine for comfort (mydirasis, relaxation of CB [cicloplegia] NB. will dry eye)
  • ciclosporin (does not interfere with stromal/epithelial healing like steroids)
    X Steroids X NOOOOO!!! also most NSAIDs no.
  • enhance collagenolsis, slow healing
22
Q

Which abx are used in the eye?

A

> Fusidic acid gel for G+s BID
chloramphenicol eyedrops for G+, good penetration, TID
aminoglycosides (gentamycin and tobramycin TID) pseudomonas may be resistant and delay epithelial healing
Fluoroquinolones (exocin and ciloxin) good penetration for G+s
- big guns?? think resistance - really necessary?
- may interfere with healing

23
Q

How may melting be prevented (or decreased slightly, but rarely ‘treated’)?

A
  • serum eyedrops (antiproteases for serin proteases and MMP)
  • frequent application TID/QID
  • supports epithelial healing
24
Q

What medical treatment can provide comfort in ulcerated eyes?

A

> mydriatic-clycloplegic, long acting: atropine
- BID for ~2d smallies, longer horses
- temporary dryness and gut stasis in horses
mydriatic but POOR cycloplegic, short acting: Tropicamide (midriacyl)
long term preservative free viscous tears

25
Q

How quickly can a melting ulcer destroy the cornea? Exceptions?

A

A week - do not wait longer than 3-5d to see

- rare excpetion = SCCEDs.

26
Q

What type of ulcer must be referred and assessed for surgery?

A
  • > 50% depth ‘pot-hole’ look
27
Q

general tx rules - what is healing aided by?

A
  • stabilisaing serum
  • granulation tissue bed
  • but healing does not depend on it - ULCER DEEPENING IS FASTER

Opthalmology (14 decks)

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