Intro to contact Lenses Flashcards
What are the different types of contact lenses?
Rigid Gas Permeable Soft Hybrids Silicone Rubber Lenses (SRCL)
Are rigid gas permeable lenses comfortable?
No they are definitely not as comfortable as soft lenses
Why are Rigid Gas permeable lenses still used if they are uncomfortable?
Myopic control –> Orthokeratology refers to the use of gas-permeable contact lenses that temporarily reshape the cornea to reduce refractive errors such as myopia.
What were the first contact lenses made from and why was this bad?
The first contact lenses were made from PMMA (Polymethylmethacrylate) - essentially glass. (They were smaller than the cornea) This was bad as glass doesn’t let air through and so hypoxia would occur thus corneal swelling and neovascularisation.
How does the size of an RGP lens relate to comfortability and why?
The bigger the RGP lens, the more comfortable it is. Small lenses move around a lot causing discomfort whereas, large lenses hug the eye staying in place.
What are the rough sizes RGP lenses come in?
Smaller than the corneal diameter Semi-scleral (so just bigger than the cornea) Scleral so border clearly exists in sclera
What are the two materials soft lenses are made out of?
Hydrogel (Hy) and Silicone hydrogel (SiH)
Why is Hydrogel a good material for soft contact lenses?
It is Hydrophilic. It has different water contents - it is the water that lets the oxygen through. The more water content you have the more oxygen can get through.
What is a disadvantage to Hydrogel as a material for soft contact lenses?
Although a high water content means more oxygen it also means more deposits are attracted to the lens. This makes it uncomfortable for the patient.
What is Silicone Hydrogel (SiH)?
A mixture of silicone rubber (it is a hydrophobic material) and Hydrophilic materials.
What is an Advantage of using Silicone hydrogel over Hydrogel as a material for soft contact lenses?
The silicone rubber in Silicone hydrogel has a high oxygen permeability (even though its hydrophobic) this paired with the hydrogel components means an increased oxygen levels reach the cornea as a result Silicone hydrogel lenses can be worn for longer!
What is the typical size of Soft contact lenses?
Larger than the corneal diameter
What is an advantage of RGP lenses?
They provide very good vision And cannot take up bacteria (thus are healthier for the eye (surface may contain bacteria but they can’t take it up)).
What is the structure of Hybrid lenses?
There is Rigid Centre (RGP) and Soft skirt attached.
What is the advantage of a hybrid lens?
The rigid centre (RGP) provides good vision whilst the soft skirt provides comfort.
What is a disadvantage of Hybrid Lenses?
They are more expensive
What does it mean to be therapeutic?
Relating to the healing of disease.
What is an advantage of Silicone Rubber Lenses (SRCL)?
They have an EXTREMELY high oxygen Permeability.
When are Silicone Rubber Lenses used?
Therapeutically only e.g. for those with Aphakia, corneal perforation, dry eyes, babies/children.
Why are Silicone Rubber Lenses only used therapeutically?
Because they are very expensive.
What is Aphakia?
Aphakia is the absence of the crystalline lens of the eye
What are indications and motivations in regards to contact lenses?
Indications are what we the optometrist think the patient needs. Motivations is what the patient wants (i.e. cosmetic reasons).
What are common motivations for contact lenses?
Cosmetic reasons - people don’t like the look of glasses Convenience Refractive/Pathological condition Expectations and Preconceived Ideas about Contact Lenses
What are some indications for contact lenses?
Refractive (Prescription) Pathological condition in which they may need them Cosmetic (coloured contact lenses) Sports (Contact sports or ones with fast head movement) Occupational reasons (e.g. sportsperson, armed forces, entertainment industry).
For myopes is visual acuity improved or decreased when comparing contacts to glasses?
Contact lenses provide a higher visual acuity for myopes than glasses
What is the benefit of contact lenses for myopes?
Improved acuity when compared to glasses Greater Field of View They can provide myopic control
What are the benefits of contact lenses for Hyperopes?
Greater Field of view
Why may acuity be decreased (when compared to glasses) for hyperopes when contact lenses are worn?
There is a possibility that the decreased acuity is due to decreased magnification and fluctuating accommodation.
Why is acuity for astigmatic patients reduced (compared to that in use of glasses) when wearing contact lenses?
Contact lenses move around very slightly but they still move. This changes the axis of the Cyl.
In what cases of astigmatism may contact lenses be more successful at providing acuity equal to or similar to that provided by glasses?
If the patient is Myopic and if the DC< DS (cyl is less than sphere).
What are some refractive conditions where contact lenses would be indicated?
Anisometropia- the difference in prescription in a lens can make the lens feel unbalanced so contact lenses would be more (visually) comfortable. Binocular vision problems which could be solved using Toric or bifocal contact lenses.
What is uniocular anisometropia?
Where one eye has a prescription of plano (so nothing wrong) and the other eye has a prescription of over plus or minus 2 dioptres.
What is binocular anisometropia?
Where both eyes have prescriptions however these vary by over plus or minus two dioptres.
What is a binocular vision problem that is difficult to solve using contact lenses?
Prism - unfortunately you can only correct one prism in the vertical direction.
What is a Scotogenic contact lens?
A contact lens used for treating binoular diplopia. (It has a sort of blacked out centre).
What are pathological indications for the use of contact lenses?
- Cranio-facial anomalies - things such as trauma which mean you can’t put frames on the patient. 2. Allergies to frames 3. Irregular cornea 4. Keratoconus - bulging of the cornea- this creates irregular astigmatism (meridians aren’t at 90 degrees). 5. Aphakia 6. Bandage 7. Protection 8. Cosmetic
What is a contraindication?
(of a condition or circumstance) suggest or indicate that (a particular technique or drug) should not be used in the case in question.
What are contra-indications of using contact lenses? (These don’t always mean 100% they can’t wear contact lenses - just things to consider when prescribing).
Occupational concerns– e.g. exposure to: dust, chemical vapours, PC use, poor ventilation. (It’s not that people exposed to these can’t - it’s just something to consider when prescribing). • Allergies – hay fever, eczema, sinusitis • Poor hygiene – recurrent conjunctivitis, blepharitis, herpes zoster, smoker • Ill health- may existing conditions make contact lenses unsuitable? – as a result of any health condition that has implications on tear film quality (Diabetic mellitus, hyper or hypothyroidism, arthritis, menopause) • Age – ability to handle CL (infant, student, presbyopes)
How long should contact lenses be worn for?
Ideally no longer than 12 hours a day but patients will often wear them for much longer.
What’s the Link between diabetics and contact lens wearers?
Those with diabetes find wearing contact lenses not as comfy.
How are slit lamps used in regards to Contact Lens Prescribing?
They are used in a contact lens fitting for baseline measurements and aftercare to check for lens fit, surface condition and ocular integrity.
What are concretions?
Little vacuoles or cysts filled with lipid
What are high, low and medium magnifications on a slit lamp used to look at in regards to the eye?
– Low 6-10x for general eye – Medium 16x for structures – High 25-40x for detail
What would low magnification on a slit lamp be used to look for?
- Lids/lashes • Cornea • Conjunctiva • Sclera
What would medium magnification on a slit lamp be used to look for in regards to Contact Lens Prescribing?
-Blepharitis • Meibomian gland dysfunction • Concretions • Corneal staining
What would medium magnification on a slit lamp be used to look for in regards to Contact Lens Prescribing?
-Epithelial changes • Stromal striae and folds • Endothelial folds, blebs, and polymegethism
What is your responsibility if you find any sign of corneal hypoxia in a contact lens patient?
Take the contact lens out. Not allow the patient to wear any lenses until the problem goes away and teach the patient about proper contact lens care.
What are Stromal Striae?
Fine grayish white lines in the corneal stroma. These represent localized separations of the highly ordered collagen
What are Stromal Folds?
More advanced striae where fluids have caused localized undulations (up and down outlines) or wrinkles in the cornea.
What do Stromal Striae lead to?
Stromal Folds
When are Stromal Striae or Folds present?
When corneal oedema is occuring.
What effect do corneal Straie or folds have?
They cause a loss of vision. (milky cornea).
What does the cobalt blue filter on a slit lamp do?
Excites Fluorescin
What does the green (red-free) filter do on a slit lamp?
Enhances contrast of blood vessels and rose bengal staining
What does the ground glass filter on a slit lamp do?
Diffuses beam to give broad unfocussed illumination
What does a neutral density filter on a slit lamp do?
Reduces beam brightness, increases patient comfort
What does a polarising filter on a slit lamp do?
Reduces specular reflections when used in crossed pairs
What is fluorescein staining used for in slit lamp?
It highlights epithelial defects as it stains areas of missing cells.
How long does it take the fluorescein dye to disapear?
2-4 minutes.
What filter/filters in slit lamp do we use in conjunction with fluorescin staining?
Cobal blue Filter however we may also use a Yellow (Wratten 12) filter to improve contrast.
(When a wratten 12 filter is used then you are looking out for green and everything that was previously blue is now black- essentially its like putting a yellow filter over a blue filter).
Do we add fluorescein to an eye that’s wearing a soft contact lenses?
No because fluorescein stains everything including the lens. The only time we would do this is if we are trying to check for the presence of a contact lens.
What is lissamine green stain used for?
Lissamine green is used in dry eye examinations . It stains dead and degenerative cells, but not healthy epithelial cells
What slit lamp filter is lissamine green used in conjunction with?
Red (Wratten 25) filter is used to enhance staining
When does optimum staining for lissamine green occur?
1-4 minutes
Does lissamine green stain cause discomfort for the patient?
A little
Which stain is more tolerable, Lissamine green or Rose Bengal (RB)?
Lissamine green
Is rose bengal stain uncomfortable for pateints?
Yes - It Stings!
What is Rose Bengal Stain and what does it do?
A fluorescein derivate that is able to bind to epithelial cells that are uncoated by certain proteins (mainly mucin).
It stains dead cells and healthy ones that are unprotected by an intact mucin layer
What are microcysts and why are they an important thing to look out for in regards to contact lens checking?
A tiny lesion filled with dead cell material.
They are very distinct and a definite indicator of contact lens induced hypoxia.
How can retro-illumination on slit lamp be used to identify vacuoles and microcysts?
Essentially both microcysts and vacuoles are spaces in the epithelium that are filled with either a gas or fluid. This means that the light that comes back from a point that you have illuminated is defracting/diverging or refracting/converging.
Whether the light hitting you back diverges or converges depends on what the space is filled with ( either gas or fluid -i.e. whether its a vacuole or microcyst).
What you would see in this case is like small circles that are half light and half black depending on where shadow has been created. - see picture attached.
What are vacuoles in the eye?
Cyst like inclusions (something embeded) which is filled with gas or fluid
Where do microcysts and vacuoles exist if they are present?
In the corneal epithelium
How can you diffrentiate between a microcyst and a vacuole using a slit lamp ( and retroillumination)?
So if the circle that you suspect to either be a vacuole or microcyst indication has a shadow on the same side as ur beam of light then its a microcyst. If the shadow is on the opposite side to the side where the beam of light exists then its a vacuole.
Why would there be a smile line staining pattern during corneal staining?
The patient doesn’t blink fully - the bottom part of their lensdries out - often from staring at computer
What contact lens patients may have dessication 3 & 9 staining ?
(3 and 9 refer to location on a clock)
Rigid Hard Contact Lenses (RGP) lenses
When may toxicity diffuse staining be seen?
By a patient that has an allergic reaction to the contact lens.
What are the different types of corneal Staining patterns?
