22-23 diet 1 Notes Flashcards
(18 cards)
TBUT methods
- fluroscein staining method - add dye to ocular surface and ask px to blink, the time take for the first dy spot to occur is recorded as the TBUT, this is done with a blue beam on the slit lamp
- teascope method - fild oberved using special magnifiyer or instrument with a light source, tbut appears when tear film breaks and irregularities present
- lissamine green staining - can be used to stain the tear film and highlight the breakup area, providing visuals for TBUT
TBUT influence on lens selection (5 seconds)
5 seconds indicates reduced tear stability, ie this will cause discomfort for pxs who wear lenses
lens material - choose a lens that retains moisture, like silicone hydrogel or soft lenses woth high water count to prevent drying out
lens design - consider lenses with thicker lens edge or increased wettability, which helops reduce dryness.
Explain the principles of alternating design multifocal lenses and simultaneous design multifocal lenses. Discuss the challenges of fitting each of these types of contact lens. (10 marks)
Alternating design- lens deign has distinct zones for near and far vision, the wearers gaze alternates between the zones depending on weather they focus on near or distant objects
Simulteous design - lens has concentric rings of of diff powers that allow the eye to focus on multiple distances at once, brain chooses appropriate focus dependant on the viewing distances.
Challanges of fitting:-
- alternating - may caus discomfort for patients transitioning between near and distance vision. there is potential for reduced vision quality when the eyes dont align perfectly with the correct zone
- simulatenous - can cause viual distubance, such as haloes and ghosting, particularly in lower light conditions, additionally determining the optimal add power for different wearers can be challanging.
What further questions will you ask this CL patient about their reduced vision? (5 marks)
- When did you first notice the reduced vision
- was the visual problems present in both eyes
- have you experienced anhy dryness, irritatin or redness in your eyes
- Do you wear your lenses consistently, and have you experienced any discomfort
- have you noticed any changed in your Vision with your lnses in or out
Discuss five possible causes of the reduced vision in a healthy eye. (5 marks)
- lens displacement - poorly fitting lenses may be movable or rotate, affecting vision
- lens deposits - Build up of protein or debris on the lens surfcace
- Dry eye - insufficient tear film leading to blurred vision
- Hypoxia - insufficeint oxugenation to the corena
- corneal staining - fluroscein staining showing damage to corneal Epi
Explain the differences between a corneal infiltrate and a corneal ulcer. (7 marks)
Corneal infiltrates-
- refers to the accumulation of white blood cells or other inflammatory cells within the coenal stroma, typically present in a localised area of opacification without epithelial loss. can be caused by infection, inflammation or hypoxia
corneal ulcer -
- open would or lesion that affects the corneal epithelium and may extent to the stroma. is usually a result of infections or mechanical trauma, can lead to scarring or vision imapirment
Describe three possible causes of infiltrates? (3 marks)
- contact lens overwear - extended wear of contact lenses can reduce oxygen supple to the cornea causing infiltrates
- Hypoxia - insufficeint oxygen leading to ischaemia and inflammatory response
- infection - bacterial, fungal or viral infections can cause an inflammatory response leading to infiltrates
right aligned fit characteristics
Central Alignment:
The lens sits centrally on the cornea with minimal movement, as it aligns well with the corneal shape.
Even Distribution of Pressure:
The lens exerts an even amount of pressure on the corneal surface, providing optimal comfort and proper oxygen transmission.
Minimal Lens Movement:
During blinking, the lens moves slightly (about 0.25 to 0.5mm) in sync with the eyelid, ensuring proper tear exchange underneath.
No Peripheral Compression:
The lens does not press too hard on the peripheral cornea, avoiding any discomfort or irritation.
Proper Edge Fit:
The lens edge conforms to the cornea’s curvature, creating a smooth transition between the lens and the cornea, which prevents lens movement or dislocation.
Visual Stability:
The alignment ensures that the lens stays in a stable position for clear and consistent vision.
Left steep lens characteristics
Lens Sits Too Close to the Cornea:
A steep fit occurs when the base curve of the lens is too steep for the cornea’s curvature, causing the lens to hug the cornea more tightly.
Minimal or No Lens Movement:
The lens exhibits very little or no movement on the eye, which can lead to poor tear exchange and discomfort. This lack of movement prevents the lens from flushing out debris or maintaining proper hydration under the lens.
Corneal Compression:
The lens may create pressure on the central cornea, potentially causing discomfort or even oxygen deprivation to the corneal tissue.
Lens Edge Constriction:
The edge of the lens can be too tight, preventing proper tear flow and leading to irritation and reduced oxygen delivery to the cornea.
Blurred Vision:
With little movement and poor tear exchange, a steep fit can result in inconsistent vision, especially when blinking or during visual tasks that involve a lot of focus changes (e.g., reading or looking at varying distances).
Increased Risk of Redness or Irritation:
Due to the lens being too tight, patients may experience redness or irritation because of the compression on the corneal surface.
Alterations made to contact lens prescription
sphere power adjusted (slighly reduced) to improve visual acuity and comfort, esp considering the lens fitting
axis canbe adjusted in order to help with confort
Describe the four toric stabilisation methods used in soft contact lenses. (6 marks)
- Prism ballast - thickened area at the bottom of the lens thagt helps maintain stability
- dynamic stabilisation - uses the blink and the eye movement to keep the eyes aligned
- dual axis stabilisation - Involves both a back anf front surface design to enhance the lens position
- peri - ballast - using peripheral ballast to help maintain stability
Factors contrubuting to intentional Non - compliance
- Cost
- px may intentionally skip cleaning or replacement of lenses to save money, espically with disposible lenses. i.e wear daily lenses for multiple days in order tp streach wear - Convenience
- intentionally neglecting proper cleaning or wear scedule due to ease. i.e sleep in lenses or wear for longer than recomended to avoid hastle of removing lenses. - lack of percieved risk-
- some believe that they can tollerate extended wear scedules and improper cleaning without any harm. i.e thinking extended wear wont lead to any problems in the long run.
Accidental non compliance
- forgetfulness
- forgot to clean / disfect lenses as they have forgot too - lack of proper knowledge
- unknowliengly neglects certian aspects of lens care as they are not aware of importance of proper lens care - incorrect lens care technique
- can occur if px has incorrect technique.
How to support px with lens care compliance
patient education
setting clear expectations and reminders
personalised recommedations
follow up appointments
RGP lens care and long term maintainance
- insert lens
- wash and dry lenses
- inspect the lens
- position the lens
- position the eye
- insert the lens
- blink and adjust - Removal of RGP lens
- wash and dry eye
- position the eye
- push eye lid up and use lid margin to create air undet the lens and pop the eye
- place in solution - cleaning of lens
- rinse with solution
- clean the kens
- rinse again
- disinfecting
- never use water - storing RPG lens
- cleaning the lens care
- store lenses in fresh solution
- replace the lens case
- avoid storing lenses dry - Long term maintainance
- regular eye checks
- check lenses for damage
- replace lenses as needed
- use fresh solution
- avoid over-wearing lenses
Why to verify an RGP lens in practive
- to ensure correct lens
- assess visual performance
When to verifiy in practice
- after initial fitting
- durring follow up appointment
- if the px experiences discomfort
Compare and contrast cast moulding and lathe cutting in the manufacture of RGP lenses. (6 marks)
Cast moulding advantages:-
- effectiveness
- consistincy
- cost effective
cast moulding disadvatages:-
- limited customisation
- material contrast
Lathe cutting advantages -
- customisation
- material
- percision
lathe cutting disadvantages:-
- slower production
- higher cost
- tool wear
