Rigid contact lens complications Flashcards
which 2 ways are rigid lens complications classified
- by the structure that is affected
- by the aetiology/origin of that complication
list the 4 structures affected by RGP lenses
- Conjunctiva Bulbar Palpebral - Cornea Epithelium Stroma Endothelium - Tear film - Lids
which parts of the conjunctiva can be affected by RGP complications
- bulbar
- palpebral
which parts of the cornea can be affected by RGP complications
- epithelium
- stroma
- endothelium
list 4 types of RGP complications
- hypoxia
- drying
- mechanical
- toxic/hypersensitivity
what are the 4 signs of hypoxia, produced by RGPs
- Central staining
- Oedema
Spectacle blur
Striae/Folds
Corneal steepening/Corneal warpage - Endothelial Polymegethism
- Neovascularisation
what are the 6 other related signs along with central staining caused by hypoxia produced by an RGP
- Epithelial stress
- Softening of the epithelium
- Breakdown of surface
- Corneal oedema
Spectacle blur
In severe cases can = corneal steepening
and/or clouding of central cornea
Sclerotic scatter - Corneal exhaustion syndrome
- Reduced acuity
which type of RGP lens causes corneal oedema due to hypoxia
- More of a PMMA or low Dk material issue
- Esp with tight fitting PMMA/RGP lenses which restricted tear exchange
where is the oedema usually present due to an RGP lens causing hypoxia
corneal stroma
what measurement can you take in practise to look for corneal swelling due to hypoxia and why
- the cornea can only swell forwards or backwards hence can cause steepening of the cornea
- can do K readings as baseline measurement during fitting and take these readings on every aftercare to look for changes and avoid any medico-legal issues
what 2 things may a severe case of corneal oedema cause
- may affect contrast and cause light scattering
- may cause corneal clouding where it affects vision
what can corneal steepening, caused by corneal oedema due to hypoxia from an RGP be associated with
a myopic shift
which is noticed during the sight test
when may a patient with corneal oedema due to hypoxia caused by the RGP experience spectacle blur and why does this occur
- experienced following removal of the lens
- as the RGP causes the eyes to swell, it changes the power of the cornea such as PMMA lenses
- book a sight test after 1 day of not wearing the lenses
how much of swelling does an RGP or a low dk Hydrogel lens cause during the day
- 1-6%
what are the normal values of corneal swelling over night
3-4%
what does any contact lens on the eye do
restricts some amount of oxygen reaching the cornea, therefore creates a hypoxic environment
what does the epithelium start to do when it is restricted of oxygen
- it begins to respire anaerobically to conserve energy
- lactate is created as a by product of the anaerobic metabolism which goes into the stroma
when a corneal epithelium that is restricted of oxygen begins to respire anaerobically to conserve energy, what is created as a by product of this, where does this by product move to and what affect does this cause and why
- lactate is created as a by product
- the concentration increases and moves into the stroma
- this creates an osmotic effect where by water rushes into the stroma
how does the osmotic effect within the corneal stroma cause corneal/stromal oedema
because the endothelial pump cannot remove water from the stroma at the same rate as it is entering the stroma = oedema
as the oedema increases it forms, _______, _______ and at worst _______
as the oedema increases it forms, striae, folds and at worst haze
how much of corneal oedema causes striae
5%
what is the appearance of corneal striae and where about are they formed, caused by oedema
- Fine, wispy, vertical lines
- in the posterior stroma
Striae __________ as _________ increases
Striae increase as oedema increases
vision is __________ with striae produced by corneal oedema
vision is unaffected with striae produced by corneal oedema
how much of corneal oedema causes folds
8%
what is the appearance of corneal folds and where about are they formed, caused by oedema
- Depressed grooves, raised ridges
- Physical buckling of posterior stroma in response to oedema
vision is __________ with folds produced by corneal oedema
vision is unaffected with folds produced by corneal oedema
how much of corneal oedema causes haze
15-20%
what is the appearance of corneal haze and where about are they formed, caused by oedema
- Stroma hazy, milky appearance
- Gross separation of collagen fibres throughout stroma
vision is __________ with haze produced by corneal oedema
vision is affected by haze produced by corneal oedema
what is the corneal oedema stage of haze down to
not just down to the lens alone, but also other effects e.g. mechanical effects or temperature changes
what will be the solutions to oedema caused by contact lenses
- make the lens move more by fitting with a flatter lens
- change to a higher dk/t material
- fit lenses with fenestrations so the lens moves more, giving better tear exchange
what can long term hypoxia cause
endothelial polymegathism
what is endothelial polymegathism
- Structural damage to endothelial cells
- Changes to shape/size of cells
what is the long term effect of endothelial polymegathism caused by hypoxia
- corneal exhaustion syndrome
= the patient becomes intolerant to contact lenses, they are very sensitive and complain of discomfort
what is the ddx of endothelial polymegathism
Fuch’s dystrophy
what can endothelial polymegathism create problems for
future surgery
e.g. laser refractive or cataract as it can cause corneal endothelial problems, so it is important to control this by fitting with a better lens
what is the appearance of an advanced stage of endothelial polymegathism
1 cell can be up to 20x bigger than other cells
other than contact lenses, what else can cause endothelial polymegathism
ageing
but contact lenses speeds this process up
what is the debate about what happens during endothelial polymegathism
some think it is due to cells migrating out to the periphery, some say cells stay in the same place but just turn around e.g. one side is larger than the other, or some say the endothelial pump fails and causes an acidic shift
what is corneal neovascularisation (which is caused by hypoxia)
Formation of new blood vessels (neo=new) in an area usually
devoid of blood vessels - the avascular cornea
which lenses is there low prevalence of corneal neovascularisation (caused by hypoxia), and which lenses could be more associated and why
- Low prevalence of
neovascularisation with rigid lenses - Could be associated with poor (PMMA) lens fit, chronic irritation,
poor tear exchange
when can corneal neovascularisation affect vision
when it crosses the line of sight
what is the management for corneal neovascularisation
- refit with a higher Dk/t lens, or stop lens wear until the blood drains out of the shell
or - fit with a better fitting lens with better tear exchange
why will you need to monitor a patient with corneal neovascularisation very closely after management
because the blood will go out of the vessel, but the shell remains so it can easily be filled back up with blood again
what is corneal neovascularisation from an RGP caused by
poor fitting of the lens
what is neovascularisation from a SCL caused by
over wear of the lens
what are the two signs of drying caused by RGP complications
- Vascularised limbal keratitis
- 3 and 9 o clock staining (mechanical origin)
what is vascularised limbal keratitis, caused by dry eyes
A chronic CL induced irritation
(mechanical), inflammatory reaction which produces a Semi-opaque corneal nodule, ‘pseudopterygium’
what is vascularised limbal keratitis, caused by dry eyes associated with and therefore what will be the management
- inadequate lubrication and low edge lift
- change the firing of the lens if due to low edge lift
what is the ddx of vascularised limbal keratitis, caused by dry eyes
pterygium (but this can invade the cornea and affect vision)
what is the other positions of 3 and 9 o’clock staining
4 and 8 o’clock staining
what type of staining is 3 and 9 o’clock staining
Coalesced superficial staining
as well as 3 and 9 o’clock staining, what other sign does vascularised limbal keratitis as a result of drying produce
Localised superficial and stromal
vascularisation
what 2 types/categories of 3 and 9 o’clock staining are there
- Mechanical/Drying
and/or - Impression from lens
edge (= poor fitting of lens)
what are the 5 signs of 3 and 9 o’clock staining
- Usually bilateral
- Staining
- Dellen
- Vessel encroachment
- Opacification of tissue
what is dellen (a sign of 3 and 9 o’clock staining)
it is a depression at the side of the cornea formed from an impression
list the 8 causes of 3 and 9 o’clock staining
- Poor or incomplete blinking
- Poor tear film
- Large eye (wide palpebral
aperture) - RGP material
- Excessive edge clearance
- Edges to thick
- Total diameter too large
- Total diameter too small
list 9 solutions/managements of 3 and 9 o’clock staining
- Break from lens wear- (esp if moderate)
- Correct blinking
- Change care regime, ocular lubricants
- Refit with different material (e.g. soft lens as has a wider diameter)
- Refit with a soft lens
- Refit with lid attachment design
- Different TD
- Different peripheral design
- lots of lubrication so the eye doesn’t dry out
why do RGP lenses cause mechanical effects to the eye
because they’re a rigid/hard material
what 7 things can mechanical changes from RGP lenses to the eye cause
- Corneal shape changes
Corneal topography changes and corneal warpage
Fischer-Schweitzer pattern - Lens binding
- Dimple staining
- Foreign body tracks
- Ptosis
- Contact lens associated palpebral changes (mechanical or allergic)
- 3 & 9 o clock staining (mechanical origin)
what is the main lens associated with corneal shape changes/warpage
ill fitting PMMA lenses
what is useful for monitoring corneal shape changes/warpage
corneal topography
should be done before and after contact lens fitting
what may be contraindicated with corneal shape changes/warpage
refractive surgery
what is the wrinkling of bowman’s membrane called
Fischer-Schweitzer pattern
what is the appearance of Fischer-Schweitzer pattern
polygonal mosaic
what is Fischer-Schweitzer pattern caused by
it is a stress indicator, caused by stress of a rigid lens rubbing on the cornea and also caused by rubbing the eye
how far can a Fischer-Schweitzer pattern extend over the cornea
it can be localised or can cover the whole cornea
when does Fischer-Schweitzer pattern disappear and how
- on lens removal
- as the cornea bounces back into shape
what is the ddx of Fischer-Schweitzer pattern
epithelial wrinkling
describe the association, appearance and symptoms of epithelial wrinkling (which makes it different to Fischer-Schweitzer pattern)
- Rare
- Associated with soft CL
- Small lines or furrows, at any
angle - Very painful
- Vision affected
what causes lens binding
an immobile, decenetred lens
due to eyelid pressure, forming an indentation of the cornea by lens edge
what can be noted inside from lens binding due to the indentation of the cornea by lens edge
superficial punctate keratitis
what type of effect does lens binding have on the eye
suction effect
what may a patient experience with lens binding
difficulty in removing their lens due to the suction effect
what may be seen on removal of a lens with lens binding
indentation staining
what is the management of lens binding
- alter the lens fit and aim to increase mobility
- cease lens wear temporarily
what is simple staining/veiling
small bubbles which become mechanically compressed between the lens and the eye, causing indentations in the corneal epithelium
what is the cause of dimple staining/veiling
poor lens fit relationship between cornea and posterior
lens surface
what is the management of dimple staining/veiling
- Remove lens (to let the eye recover)
- Modify fit
when can dimple staining/veiling disturb vision
if its in the middle of the visual axis
with which lenses are foreign body tracks more common
in PMMA lenses and RGP lenses rather than soft
what type of appearance does foreign body tracks have and why
Linear staining-indicates path taken by FB = scratched cornea
what are the symptoms of a foreign body track
– Lacrimation
– Discomfort
what must you assess with foreign body tracks and how
the depth and extent by doing an optic section on slit lamp
what is the management for foreign body tracks
Remove lens (search for the FB), address cause, maybe replace lens
why should you know which FB is causing the FB track
to know if it is a dangerous particle or a sterile substance e.g. if from the soil, it can be fungal which can lead to dangerous conditions
what can cause ptosis
- Long-term wearers of PMMA or RGP lenses
- Possibly due to lens removal procedure of pulling laterally on
the eyelids followed by a harsh blink - Other causes may be the constant rubbing of the lens edge
against the palpebral conjunctiva
what will you want to exclude when assessing contact lens related ptosis
other serious neurological causes
what can be the management for ptosis
- could try soft lenses or cease wear
- or explain to patient not to be so aggressive with RGP lenses
where is CL associated palpebral changes located and what appearance does it have
- Towards the lash margin (underside of eyelid)
- Crater-like form
- Often appear as round light reflexes, giving an irregular specular reflection
how can you tell if someone with contact lens associated palpebral changes has it due to mechanical reaction
they will have a delayed reaction
what is the aetiology of someone who has immediate contact lens associated palpebral changes
if it is allergic
what can be a allergic cause for a patient who has contact lens associated palpebral changes
lens solution toxicity
contact lens associated palpebral changes is caused by continual interaction with the __________ ___________
contact lens associated palpebral changes is caused by continual interaction with the tarsal surface
the cause of contact lens associated palpebral changes can be ___________ or _________
the cause of contact lens associated palpebral changes can be mechanical or allergic
what are more numerous in allergic contact lens associated palpebral changes
the papillae
where are the papillae located with allergic contact lens associated palpebral changes
closer to the fold of the eyelid
what is the appearance of the papillae in allergic contact lens associated palpebral changes
the apex of the papillae take on a rounded, flatter form
what is the management of allergic contact lens associated palpebral changes
frequent replacement
what is the main cause of solution toxicity
sensitivity to the preservative
what are the signs and symptoms or solution reaction
- Localised epithelial reaction
(Superficial punctate keratitis) - Conjunctival hyperaemia
- Burning sensation
what can be a management of a solution reaction
switch to daily lens to avoid solutions all together
