23/24 diet 2 Notes Flashcards
(15 cards)
Steps in assessing the fit of a SCL
- lens position - centralisation
- lens confort - px comfrot
- les movement - typiaclly 0.25-0.5 mm
- lens edge fit
- tear exchange - observe tear film
- lens movememt and VA
advatages of silicone hrydogel
Higher Oxygen Permeability: Silicone hydrogel lenses allow significantly more oxygen to pass through the lens, improving corneal health and reducing the risk of hypoxia compared to traditional hydrogel lenses.
Extended Wear Options: These lenses are often approved for overnight wear because of their high oxygen transmissibility.
Improved Comfort: Silicone hydrogel lenses tend to be more comfortable for long wear due to their moisture retention and reduced dryness.
Disadvantages of siliconme hydrogel
Increased Cost: These lenses are generally more expensive than traditional hydrogel lenses.
Less Wettable: Silicone hydrogel lenses can have lower wettability, which can cause discomfort or dryness for some patients, requiring regular lubrication or specific cleaning solutions.
More Rigid: The material can feel firmer than traditional hydrogel lenses, which can lead to initial discomfort for some wearers.
Oxygen permiability vs transmitability and imprortance
Oxygen permiability (Dk):-
refers to the materials ability to transmit oxygen, measured by thr Dk value. Higher Dk value means more O2 reaches the cornea, promoting corneal health.
Oxygen transmitibility (Dk/t):-
Takes into account the thickeness of the lens and its materials Dk value, indicates how much oxygen can actually pass though the lens to the cornea durring wear.
Importance:-
- corneal health: suffient oxygen is crucial for avoiding hypoxia, preventing oedema, and promoting healthy tear exchange
- comfort and safety: proper oxygen level help maintain comfort and redice the risk of complications like infections or irritation from long term wear.
signs and symptoms of keratitis
Signs:-
- corneal staining
- increased redness
- pus or discharge
- corneal opacities
symptoms:-
- severe pain
- visual disturbance
How to manage microbial keratitis by optometrist and opthalmologist
Optom role:-
1. initial assesment - optom would assess the severity and location of the infection thought the slit lamp, cheaking for signs like corneal staining and discharge
2. referral - if microbial keratitis is suspected, an urgent referral to an opthalmologist for specilised treatment is required.
Opthalmologist role:-
- treatment eith antibiotics
- culture and sensitivity training
- close monitoring
Measurments needed in order to order a toric RGP lens
keratometry readings
prescription
base curve
lens diameter and power
Benefits of an RGP over a soft contact lens
- better visual acutiy
- longer lens life
- higher oxygen transmitability
- imprived eye health
- custom fit
- lower long term cost
diff between spherica and asypherical RGPS and why asypherical are better
Spherical:-
- design: a structural RGP lens has has a uniform curvature across its surface, designed to provide the same optial power in all directions
- use: typically ised for patients with regular corneal shapes and no significant astigmatism
Aspherical:-
- design: an aspherical RGP lens has a gradually cahnging curvature across the lens,, ehich allows or improved optics, espically for patients with irregualr corneal.
- use: aspherical lenses can correct both spherical and astigmatic refractive errors and are particularly usefuk for irrrgular corneal shapes.
Advantages for aspherical lenses:-
1. Improved visual quality - aspherical lenses reduced optical abberations like flare, distortion and haloe effects, leading to sharper vision.
2. Better comfort:- aspherical lenses can provide a closer fit to the cornea, reducing thr risk of lens movement and imroving tear exchange, which leads to better comfort durring wear.
CPLU vs CALRE
CPLU: -
- Pain - severe, sharp pain, particularly when blinking
- Visual disturbance: px may experience blurry vision or difficulty focusing, espically if ulcer is centrally located.
- discomfort - foreign body sensation
- Durration - symotoms typically persist as the ulcer progresses
CLARE:-
– Mild to moderate pain
- Redness adn irritation - due to inflammation from hypoxia or lens related issues
- visuaol disturbance: less common, vision genrally unaffectdd unlesss accompanied by other complications
signs of CPLU vs Clare
CPLU:-
- peripheral corneal infiltrates
- corneal oedema
- infections signs
- conjunctival injections
CLARE:-
- Diffuse redness
- no ulceration
- mild discharge
Contrast:-
- CPLu presents with a more localised ulceration and severe pain, wheres CLARE involves generalised redness and mild irritation, typically whthout significant pain or corneal damage
Simultaneous design contatc lenses for presbyopia
Optical Principles of Simultaneous Design Lenses:
Simultaneous design lenses contain multiple zones within the lens, such as concentric rings of different powers for near and far vision. The wearer’s brain selects the appropriate focus based on the distance they are looking at, allowing the lens to provide near, intermediate, and distance vision simultaneously.
This is ideal for presbyopes, as the lens does not require the wearer to switch focus between separate zones like bifocals or monovision.
Advantages:
Convenience: The wearer does not need to adjust their gaze to different zones for near or distant vision.
Better Depth Perception: The brain blends images from both near and distance zones, providing more natural depth perception compared to other designs like monovision.
Visual Clarity: Multiple zones provide clear vision at different distances, reducing the need for reading glasses or additional lenses.
Disadvantages:
Adaptation Period: Some patients may experience visual disturbances like halos or glare, especially at night.
Compromised Near Vision: In some cases, near vision may not be as sharp as that provided by dedicated near-zone lenses, such as bifocals or monovision.
Limited Effectiveness in Low Light: Simultaneous designs may not perform as well in low-light conditions due to the way the brain selects focus from multiple zones.
factors to consider when making decision about suitability of patients for extended wear contact lenses
Factors to consider:-
- ocular health (assess dry eye and / or ocular surface disease)
- lens material and oxygen permiability
- patient compliance
- age and health of px
- lifestyle and occupational considerations
- corneal curvature and lens fit
- fequency of follow up
lens compliance issues that can be resolved by moving a patient from reusable to daily lenses
- lens cleaning
- lens case contamination
3.inconsistant repalcement scedule - lens overware
5.improper handeling and insertion
Possible consequences of non-compliance
infections
hypoxia and corneal oedema
dry eye and discomfort
corneal stiaining and ulcers.
