Low vision and visual rehabilitation Flashcards
What % of patients that go to LVA are under 16 years old?
5%
What 6 conditions/reasons do children go to LVA for?
- Congenital cataracts - most common
- Optic atrophy (often 2o)
- Albinism
- Buphthalmos
- Myopia
- Retinopathy of prematurity
What % of patients that go to LVA are adults in the employable age group?
25%
What 6 conditions/reasons do adults go to LVA for?
- DR
- Myopia
- Uveitis
- Corneal dystrophies
- Macular degenerations
- Retinitis pigmentosa
What are 2 clinical features of congenital cataracts in children?
- Occurs in first few months of life
2. Absence of red reflex
Why is it important to address congenital cataracts in children?
Need to stimulate development of visual pathways
What is buphthalmos in children?
Congenital glaucoma – problem with drainage angle so pressure rises, and eye expands, leading to enlargement of eyeball
Are children usually born hyperopic or myopic?
Hyperopic
What happens to shape of eye as a child grows up?
Elongates
What are 4 common causes of visual impairment in the elderly?
- Age related macular degeneration (dry/wet) – most common
- Glaucoma
- Inoperable cataract
- DR and maculopathies
What % of LVA patients are retired/elderly age group?
70%
What are the 7 principles of vision assessment?
- Clear diagnosis and make sure patient has a good understanding of their problem and realistic expectations of what optometrists can do for them
- Identify patients practical needs/assess expectations e.g. problems with reading/watching TV/cooking etc
- Record distance unaided vision i.e. Snellen chart
- Retinoscopy – objectively assessing someones prescription i.e. holding lens in front of the eye + shine light with torch
- Subjective refraction – ask patient to tell you if different lens have any benefit etc
- Near vision assessment e.g. N10 (size of print) at 25cm with +4.00D add
- Unit magnification assessment
What is unit magnification? How does it work?
4
- Determines patients distance refraction/correction
- Ask patient to view reading chart at 25 cm, then determine best near acuity at this range e.g. N10
- Ask patient what size is required for desired tasks
- Calculate magnification required to achieve this
What are logMAR charts? How is it different to Snellen?
“
- Used more in research/clinical setting – good for people with visual impairment.
- More subjective – 5 letters per line and decrease down in size evenly in a logarithmic fashion so it is more fair. However there is more crowding as you go further down.
What is a General referral GOS (18) form?
4
- Standard referral for patients from the community to hospital i.e. optometrists refer to hospital eye service via GP
- Referral by optometrist: sign of injury, disease or abnormality and treatment or further investigation required, or unsatisfactory level of VA even with corrective lenses
- Information by GP: Screening and monitoring diabetes and patients with glaucoma
- Referral implies transfer of responsibility to GP
If urgent treatment is needed, how does an optometrist directly refer to hospital?
Directly refers, but needs to notify GP by phone/fax
What are the 2 different sections of GOS (18)?
Section 1 - Completed by optometrist
a. Patients details
b. Sight test details and acuities
c. Disc appearance, IOPS and visual fields
d. Points of interest
Section 2 – complete by GP
a. Relevant clinical and social history
b. BP, urinalysis, provisional diagnosis
What are the 3 specific visual impairment referrals?
LVI – letter of visual impairment
RVI – referral of visual impairment
CVI – certificate of visual impairment
What is the definition of visual impairment?
A person who is ‘substantially and permanently handicapped’ by defective vision caused through congenital defect, illness or injury
What are the objective definitions of visual impairment (3)?
VA – 3/60 to 6/60 on Snellen chart
OR
Up to 6/24 with moderate fields contraction
OR
VA 6/18 or better if severe field loss (advanced glaucoma, retinitis pigmentosa or hemianopia)
What is an LVI (3)?
- Referral form for use by optometrists or clinicians outside the HES
- Given to patients with significant difficulties to help seek advice from a council with social services (SS) responsibilities
- Patient fills in the details
What is an RVI (2)?
- Can be used by non-ophthalmic staff
2. Can be used to allow patient to access social services
What is CVI (4)?
- Document patients level of vision – certificate of a person as sight impaired or severely sight impaired/blind
- Patients can volunteer to have it done
- Gives them access to social services
- 3 parts:
a. Opthalmologist i.e. visual function
b. Other relevant factors e.g. lives alone, hearing, mobility
c. Patient consent to registration
What is vision (2)?
- The level of vision that an eye can resolve unaided
- Determined by the size of the smallest line of letters or symbols on the test chart that can be read without any form of optical correction in place
What is visual acuity (2)?
- A measure of the eye’s ability to resolve fine detail with the optimum optical correction in place
- Determined by the size of the smallest line of letters or symbols on the test chart that can be read after any defects of focusing, other than aberrations have been corrected
What is accomodation?
The ability of lens to change the shape resulting in change of power
How does the lens accomodate (3)?
- Ciliary muscle contracts
- Zonules relax
- Lens assume a more convex shape
What is presbyopia?
With age, the crystaline lens undergoes sclerosis resulting in accommodative ability causing an inability to focus on near objects
What are 2 methods of testing visual acuity?
- Snellen chart
2. LogMAR chart
When measuring near vision, what does N6 mean?
N = notation 6 = size of print
What are the 3 main refractive components of the optical system?
- Cornea
- Lens
- Axial length
What is a dioptre?
The unit of measurement of the optical power of a lens or mirror
It describes an ability to bend or refract rays of light so light is focused accurately onto the fovea
What does emmetropia mean?
Optically perfect eye
What are the dioptres of the cornea and lens, and axial length in an emmetropic eye?
Cornea = 40D
Lens = 20D
Axial length = 22.22mm
What is ametropia?
One or more of the optical parameters are ‘less than perfect’ and therefore an optical or focusing error occurs
What happens in myopia?
Light is focused in front of the retina
short-sightedness
What are the 2 types of myopia?
- Refractive myopia
- Effective power of eye too strong >60D - Axial myopia
- Eye is too long, >22.22mm
- Corrected with divergent lenses
What type of lens corrects myopia and how does it work?
Divergent
Light rays spread out and focus pushed back on to retina
What happens in hypermetropia?
Light is focused behind the retina
What are the 2 types of hypermetropia?
- Refractive hypermetropia
- Effective power of eye too weak, <60D - Axial hypermetropia
- Eye is too short, <22.22mm
- Corrected with convergent lens
What lens corrects hypermetropia and how does it work?
Convergent
Light rays contracted and focus pulled forward on to retina
What is an astigmatism?
Eye is shaped like a rugby ball - symmetrical in shape in all but one direction. Therefore light will be refracted in the same manner over all most of the eye, forming a point focus as normal. Light striking the eye in the direction of the asymmetry will be refracted in a different manner and thus a second point focus will be formed
What is the correction of the astigmatism?
A convergent or divergent lens will correct the main refraction error.
An additional lens with power in one direction only will then be used to correct the residual astigmatic error - a cylindrical or toroidal lens
What are 2 alternative methods of correction to glasses?
- Contact lenses
2. Refractive surgery
What is the pinhole used for?How does the pinhole work?
Pinhole can help to differentiate between reduced VA due to uncorrected refractive error and a pathological cause.
It reduces the blur circle and induces a point focus within the eye
If VA is corrected with pinhole, what does this mean?
There is uncorrected refractive error causing the redeuction in VA
If a VA is not corrected with pinhole, what does it mean?
Underlying pathological cause
What are 5 advantages of soft contact lenses?
- Flexible
- Good initial comfort
- Larger diameter incurs secure fit
- Safer for sport
- May be used for extended wear
What are 7 advantages of rigid gas permeable lenses?
- Fixed shape and durable
- Good for all-day wear
- Smaller diameter incurs less risk of hypoxia
- Creates smoother ocular surface therefore better
- Visual result for irregular corneas and high astigmatism
- Easy to clean
- Good VA if large elvels of astigmatism
What are 4 disadvantages of soft contact lenses?
- Splits easily
- Depositions from tear
- More expensive
- Dehydrates if left out of the solution
What are 2 disadvantages of rigid gas permeable lenses?
- Poor initial comfort
2. Smaller diameter therefore prone to fall out of eye
