Lens Disorders Flashcards
What is the pathophysiology of cataracts?
Changes to biochem composition and structure which continues throughout life
Result in loss of lens fibre and elasticity and accommodation
What is oxidative stress?
Free radicals cause change in cell structure
This alters proteins that allow lens to have transparency
What cause light scatter?
Protein denaturation and intercellular spacing
What increases from birth and age?
Nuclear fibres
What is coronal?
Equatorial section of lens
What is the lens function?
Transmit as much light with minimal optical defocus
What are the primary features of the lens?
Absence of BV
Lack of cell organelles
Regular and tight fibres
Where are the epithelial cells located?
Anterior surface
What is the primary driver of light scatter?
Refractive index b/w adjacent structures
Where is light scatter greater in the lens?
Cortical layers
Where does the lens receive its nutrients?
Aqueous humour diffusion
What are the fibres shaped to reduce scatter?
Hexagonal
What are interdigitation?
Form of tongue and groove joint- allows movement but minimises the between fibre spacing
What type of light scatter gives cataracts like sxs?
Forward
How is backward light scatter formed?
Media opacities
What is the point spread function?
Being able to measure degree which ocular media spreads that point function
What 2 factors influence point spread function?
Abberation
Light scatter
What is veiling luminance?
Scattered components randomly distributed across entire retina?
When is vision greatly decreased?
Very bright sunlight
Sun low in the sky
Reflected sun
What are considered lower ordet abberation?
Regular astig
Positive and negative defocus
What are considered higher order abberation?
Irregular astigmatism
Spherical, coma trefoil
In light of high and low order Aberations, how would this effect vision?
Increase in any of these would cause blurred vision sxs
With high order aberrations, what sxs could be induced?
Night vision, halves, stardust pattern, monocular dip
What sxs could be presented with glare?
Stars/ halies around light
Pain/disc if close to fixation
Increase proximity
How does nuclear cat come about?
Age and protein related changes
What are chromosomes?
Molecules responsible for visible color Absorb visible light Reduced retinal illumination Absorbs blue end Lens appears yellow/brown 'Washed out'
What are the potential sxs in nuclear cat?
Blurred vision
Glare
Altered colour vision
How does cortical cat come about?
New lens fibres grow from epithelial cells and can become over hydrated leading to protein changes and reduced transparency
What are the pretensions of cortical cat?
C shaped crescents- spoked shaped from periphery, shade type opacities
Which type of cat is most common?
Cortical 30% >45 yrs old
What sxs are presented in cortical cat?
Asymptomatic… symptomatic if pupil involvement (blurred vision, monocular dip, glare)
Where is the most common location for cortical and why?
Interior and infranasal
Uv exposure
How is PSC formed?
Epithelial take a different path and migrate towards posterior pole… become vacuole shaped
What are PSC presentations?
Circumscribed, circular at posterior pole
What sxs accompany PSC?
Blurred vision
Glare
What test could be carried out to distinguish glare and blur?
Contrast sensitivity measurement
Dilating the pupil
Which cat type decrease contrast sensitivity more compared to others?
PSC
What are the possible causes for congenital cat?
Mainly Idiopathic
Metabolic disorders
Sytemic abnormalities
Chromosome abnormalities
What are the signs of congenital cat?
Bilateral
Symmetrical
What is subluxated and what can cause this?
Anomoly where lens no longer centred to pupil, AKA: Ectopia lentis
CAUSE: Traumatic displacement
Development anomaly
Genetic disorders- marfans syndrome
What is included in a pre op assessment?
Biometry Refractive goals Monovision Astigmatism Accommodation IOLs multifocal/Accom IOL
What are the risk factors of cataracts?
AGE Smoking UV radiation Diabetes Trauma Medications
What type of meds may increase risk of cataracts?
Corticosteroids (Cortical)
Chlorpromazine (PSC)
In terms of refractive goals, what can be a real issue?
High pre opp rx
How would monovision IOLS work?
NV rx IOL 1 eye and emetrope IOL in other eye
When should an individual be seen for a sight test post op?
3/52
What factors should an optom consider for a cat surgery?
Effects vision and quality of life One eye or BE effected Risks and benefits of surgery Quality of life if opt NOT to have surgery If px WANTS surgery
When is cat surgery indicated irrespective of visual performance and sxs?
Compromised iris anterior drainage angle= increase risk of IOP elevation
What do direct referral schemes involve?
Full eye exam- lens assessment and fundoscopy (retinal path with pupil dilation)
Discuss pros and cons
Where px would like to be assessed
What can optoms do to manage those with cat?
Correct refractive error Dispensing - Absorptive tints - UV absorber - Anti reflection coatings Nutrition
Who would benefit with a tint?
Beneficial for PSC however detrimental for cortical
In all cataracts, what should be considered?
Pupil size, depth of focus, retinal defocus
What is the most popular surgical intervention for cataracts?
Phacoemulsification
