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Ophthalmology > 6. Refractive Errors and Paeds > Flashcards

6. Refractive Errors and Paeds Flashcards

1
Q

How does one assess visual acuity in Adults?

A

Snellen Chart

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2
Q

Describe the Snellen Chart procedure and how the result is arrived at?

A

Patient sits at 6 meters from chart

Vision expressed as a fraction – eg 6/36 – means that at 6m from the chart, patient can read what someone with “normal” vision would be expected to read from further back at 36m

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3
Q

What should be checked if the patient cannot read the top line of a Snellen Chart?

A

CF – count fingers?
HM – hand movements?
PL – perception of light?
NPL – no perception of light?

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4
Q

Term used to describe ‘no refractive errors’

A

Emmetropia

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5
Q

Term used to describe ‘shortsighted’

A

Myopia

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6
Q

Term used to describe ‘longsighted’

A

Hyperopia

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7
Q

Term used to describe when two eyes have unequal refractive power.

A

Anisometropia

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8
Q

Loss of accommodative power with increasing age.

A

Presbyopia

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9
Q

Decreased vision that results from abnormal visual development in infancy/childhood

A

Amblyopia

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10
Q

Blurred vision due to irregular shape of cornea – making it difficult to get light in focus on the retina

A

Astigmatism

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11
Q

What is myopia?

A

Optical power of the eye is too strong for it’s corresponding axial length, thereforethe light is focused in front of the retina – so a blurry image falls on the retina.
Often due to longer than normal eye.

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12
Q

How is myopia corrected?

A

Concave Lens (Minus)

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13
Q

What are the categories of myopia and their characteristic?

A

NON-PATHOLOGICAL MYOPIA
Usually less than 6.0 dioptres
Onset in childhood/adolescence
Usually progresses through adolescent growth phase, and stabilises in second decade

PATHOLOGICAL MYOPIA
Usually greater than 6.0 dioptres
Usually presents in early childhood and is progressive
Risk of vision threatening consequences – retinal detachment, choroidal neovascularisation

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14
Q

Discuss the different aetiological factors that contribute to myopia?

A

GENETIC FACTORS
Family history
High myopia linked to several multi-system diseases – eg Marfan’s, Ehler’s Danlos syndromes
Higher incidence in asian population (80% in asia versus 20-50% in america)

ENVIRONMENTAL FACTORS
Spending more time outdoors in childhood appears to be protective
Higher incidence in people who spend more time doing near work (reading, computers etc)

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15
Q

What are the pathological features/complications of myopia?

A

Tilted disc

Atrophy of chorioretinal capillaries and RPE

Risk of retinal degeneration and detachment

Risk of choroidal neovscularisation

Associated with POAG

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16
Q

What is the Tx for Myopia?

A

Glasses – minus (concave lenses)

Contact lenses

Refractive surgery

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17
Q

What is hyperopia?

A

Weaker refractive power of the eye relative to the axial length
Shorter eye

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18
Q

What is the prevalence of hyperopia

A

(10%)

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19
Q

What is the prevalence of hyperopia in neonates?

A

Most babies are hyperopic at birth – this is normal

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20
Q

Babies who have a hyperopia of >3.50d are at greater risk of what?

A

Strabismus (crossed eye)

Also some association with Angle Closure Glaucoma

21
Q

What increases the chances of excessive hyperopia in babies?

A

Family history
Maternal smoking during pregnancy
Prematurity / low birth weight

22
Q

What is the typical presentation of hyperopia?

A

PRESENTATION:
Usually in early childhood
Decreased vision/squinting for near tasks
Strabismus
Eye strain / headaches when doing near work

23
Q

How is hyperopia usually managed?

A

Glasses – plus (convex lenses)
Contact lenses
Refractive surgery

24
Q

What is presbyopia? Corrected how?

A

Loss of accommodative power with increasing age

Correct with plus (convex) lenses – reading glasses, bifocals, varifocals

25
Q

What is accommodation?

A

The ability of the eye to alter its refractive power to focus on a near target

26
Q

Describe the reflex which governs accommodation?

A

Reflex controlled by CN II (afferent) and CN III (efferent)

Conversion

Miosis = pupillary sphincter contracts due to increase in parasympathetic innervation.
Lens then becomes more convex due to contraction of ciliary muscle as a result of the increased parasympathetic innervation

(Detail: Information from the light on each retina is taken to the occipital lobe via the optic nerve and optic radiation, where it is interpreted as vision. The peristriate area 19 interprets accommodation, and sends signals via the Edinger-Westphal nucleus and the 3rd cranial nerve to the ciliary muscle, the medial rectus muscle and (via parasympathetic fibres) the sphincter pupillae muscle.)

27
Q

Why does presbyopia occur?

A

Presbyopia probably occurs due to loss of elasticity of lens and weakening of ciliary muscle – normal part of ageing

28
Q

What is the goal of refractive surgery? How does it achieve this?

A

Aim to decrease dependence of glasses and contact lenses

Designed to change the shape of the cornea – hence change the refractive power of the cornea

A computer guided excimer laser precisely sculpts the cornea to reduce refractive error.

29
Q

Name the different refractive surgical methods.

A

PRK, LASEK, LASIK

30
Q

Describe the PRK and LASEK procedures?

A
  1. Remove corneal surface epithelium with a microkeratome (PRK) or with dilute alcohol (LASEK).
  2. Apply excimer laser to corneal surface to change shape and refractive power.

PRK - corneal epithelium heals in days post-op
LASEK – push back the epithelium, heals in days post op

31
Q

Describe the LASIK procedure

A
  1. Microkeratome instrument (either blade or laser) used to create a corneal flap – then flap is lifted.
  2. Excimer laser applied to corneal stroma (ie deeper than with LASEK/PRK).
  3. Flap carefully repositioned
32
Q

What are the advantages of the PRK/LASEK procedure?

A

More suitable for thin corneas
Faster recovery of corneal nerves - less risk dry eyes
No flap – so no risk of flap dislodgement
Re-treatment possible

33
Q

What are the disadvantages of PRK/LASEK procedure?

A

Greater post-op discomfort

Longer visual recovery (often 7-10 days)

34
Q

What are the advantages of LASIK procedure?

A

Less discomfort post-op
Faster visual recovery (next day)
Re-treatment possible

35
Q

What are the disadvantages of LASIK procedure?

A

Less suitable for thin corneas
Higher risk dry eyes
Post-op ocular trauma could dislodge flap

36
Q

What are the potential complications of refractive corrective surgery?

A

Depend on procedure

Dealing with biological tissues – risk of regression, undercorrection
Risk of infection
Dry eyes
Flap problems
Corneal haze, glare, trouble with driving at night

37
Q

What are the possible causes/risk factors of a squint?

A 
Refractive error (Hyperopia, Myopia, Anisometropia)
Congenital syndromes
Family history of squint
38
Q

Why is detection and treatment of anisometropia so important?

A

In children can lead to interruption of visual development (amblyopia) and squint
In adults can lead to eye strain

(Difference in refractive error between 2 eyes)

39
Q

What is esotropia?

A

Esotropia is a form of strabismus, or “squint,” in which one or both eyes turns inward.

40
Q

What are the potential complications of a squint?

A

If a child has strabismus – they can unconsciously suppress the image from one misaligned eye to avoid seeing double. This however may lead to amblyopia and permanent visual loss.

If an adult has strabismus (eg as a result of trauma or a cranial nerve palsy) – they can’t suppress the image from a misaligned eye so they will have diplopia.

41
Q

What is Amblyopia?

A

Reduced vision occurring during the years of visual development (approx 0-8 years), secondary to abnormal visual stimulation.

When an ocular pathology (refractive error, anisometropia, strabismus, congenital cataract) interferes with normal cortical visual development

42
Q

What is the Tx for Amblyopia?

A 
Occlusion therapy (patching, atropine)
Usually treatable up to the age of about 8
43
Q

How is a squint managed?

A
  1. Correct the cause – eg correct the refractive error – glasses
  2. Occlusion therapy (patching) – to prevent amblyopia
  3. Surgical correction
44
Q

How does shaken baby syndrome come about?

A

Most common in babies aged 5-10 months
Baby cries – carer shakes baby – baby become somnolent and stops crying – reinforcing response

High risk physical damage – babies have big heads and weak neck muscles
Acceleration-deceleration forces traumatise brain (like whiplash)

45
Q

What are the signs and symptoms of SBS?

A

CLASSIC TRIAD!!!!! NNB
1. Intracranial Haemorrhage
(Usually subdural haematoma, due to tearing of small bridging veins between dura and arachnoid)

  1. Brain oedema
    (From shearing forces, diffuse axonal damage, secondary oedema, infarction)
  2. Retinal haemorrhages!!!! NNB (very specific finding).
    (Large retinal haemorrhages in all quadrants of eye, in all retinal layers (subretinal, intraretinal, preretinal)
    Retinoschisis – splitting in retinal layers (very suspicious for abuse)
46
Q

What is the prognosis in SBS?

A

Poor in 2/3 of babies
20% die outright
Remainder have long term sequelae (blindness, paralysis, behavioural changes, intellectual impairement)

1/3 have good prognosis with no long term complications

47
Q

What is leukocoria?

A

A white pupil.

i.e abscence of a red reflex in one eye.

48
Q

What are the Ddx’s in leukocoria?

A

Congenital cataract
Retinopathy of prematurity
Retinoblastoma

Ophthalmology (10 decks)

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