Questions I got wrong Flashcards
What is the lens that makes up the 0.50 Jackson cross cylinder?
+0.50 DC / -1.00 DS
What percentage of incident light is scattered by the cornea?
10%
This increases in corneal oedema and causes reduced visual acuity
Is diffraction greater at shorter or longer wavelengths?
Longer wavelengths
Pinhole improves ametropia of up to how many dioptres?
4D
What is the power of a concave mirror of radius 10cm?
Power = 1/f = 2/r
= 2/0.1
= 20D
What is the angle of minimum deviation of a crown glass prism with apical angle of 4 degrees?
Angle of minimum deviation = (RI - 1) x apical angle
= (1.5-1)(4) = 2
Where in the retina are hard exudates located?
Outer plexiform layer. Pathophysio = leakage of plasma from the inner blood-retinal layer
When doing keratometry, what does each step on a Javal-Schioltz keratometer correspond to?
1 dioptre
When doing keratometry, the power of the cornea is equal to 337.5 / (length of cornea in mm)
Yes
What sort of image is produced by a panfundoscope?
Real inverted image
What growth factor stimulates the differentiation of lens epithelial cells into secondary lens fibres?
Fibroblastic growth factor (FGF)
What is the trigger for shedding of rod photoreceptors?
First light
How long does it take for the outer segment of a rod cell to undergo complete turnover?
10 days
At what gestational age does myelination of the optic nerve start?
7 months (complete at 1-3 months post birth)
What is the principal DNA polymerase used in mitochondrial DNA replication?
DNA polymerase gamma (POLG gene)
What is the inheritance of Leber’s hereditary optic neuropathy and Kearns-Sayre syndrome?
Mitochondrial inheritance
Is HLA-B27 an MHC I or MHC II molecule?
MHC I
What are the roles of MHC I and MHC II molecules?
MHC I: expressed on all cells of the body, present intracellular antigen, recognised by CD4 T cells
MHC II: expressed on antigen presenting cells, present soluble antigen, recognised by CD8 T cells
What is the approximate volume of the orbit?
30mL
What are the 3 actions of the inferior oblique?
Extorsion, abduction and elevation
Does the superior ophthalmic vein pass within the common tendinous ring?
No
Which of the EOMs assumes a fusiform shape?
Superior oblique
Is the anterior or posterior lens surface more convex?
Posterior (6mm radius of curvature compared to 10mm)
What is the diameter of the lens?
10mm
Where in the sphenoid is the optic canal located?
Lesser wing of the sphenoid
What is the lymphatic drainage for periocular tissue?
Lateral: superficial preauricular
Medial: submandibular
Which layers of the lateral geniculate nucleus receive input from the contralateral optic nerve?
Layers 1, 4, 6
What is the blood supply to the lateral geniculate?
Dual blood supply: anterior choroidal + posterior cerebral arteries
Which laser type is absorbed by both melanin and haemoglobin? What about melanin only?
Argon blue-green: Melanin and Hb
Diode: Melanin only
What is Rose Bengal stain used for and what filter on the slit lamp is used to best visualise it?
Stains devitalised cells. Used to check for dry eye / KCS.
Red-free filter is used.
What type of image is formed by the compound microscope?
Real, inverted and magnified
What is the difference between the Bausch and Lomb vs the Javal-Schiotz/Helmholtz keratometer?
Bausch and Lomb: Object size fixed, prism doubling varied. One position instrument (no need to change positions)
Javal-Schiotz: Object size varied, prism doubling fixed with Wollaston prism. Two position instrument
What is a Hruby lens?
High negative power lens used to visualise the retina by counteracting the positive refraction of the eye. It is a non-contact lens
What colour light is used in a focimeter and why?
Green, to reduce chromatic aberration
In a standard retinoscope, what mode is shaft down and shaft up?
Shaft down = diverging
Shaft up = converging
Usually shaft down –> plano effect rather than converging effect which is the stnadard mode used
In OCT, what wavelength class of light is used?
Infra-red
In autoregulation of blood flow, which of the following leads to vasoconstriction (excluding in the pulmonary vasculature)?
a. Reduced O2
b. Reduced pH
c. Increased CO2
d. Increased BP
d. Increased BP
Increased BP –> reflex vasoconstriction to limit blood flow
Glucose metabolism in the lens typically occurs by which pathway?
Anaerobic glycolysis
Which eponymous law is used in the principle of IOP measurement (with a Goldmann applanation tonometer)?
Imbert-Fick principle: Pressure in an idealised sphere is equal to that needed to flatten the sphere divided by the area of flattening
Which of the following neuromodulators does not exert an effect on the retina?
a. TRH
b. Taurine
c. Insulin
d. Glucagon
c. Insulin
Glucagon: Neuromodulator in amacrine cells
Taurine: Acts on horizontal cells
TRH: Acts on amacrine and ganglion cells
Within the retina, which cell type contains dopamine?
Amacrine cells
What is the Bezold-Brücke phenomenon and the Purkinje shift?
Refers to the effect of luminosity (intensity of light) on perceived hue (chromaticity)
Bezold-Brücke phenomenon: As luminosity increases, all hues appear yellow-white
Purkinje shift: As luminosity decreases, all hues appear achromatic
Lesions to which location cause motor blindness?
Superior temporal sulcus
Lesions to which location cause prosopagnosia?
Lingual or fusiform gyrus
What percentage of ganglion cell axons pass within the parvocellular and magnocellular pathways?
Parvocellular: 80%
Magnocellular: 10%
What is the minimum threshold of Vernier hyperacuity?
10 seconds of arc
Is Adie’s tonic pupil more common in the old or young?
Young
In an electroretinogram, above which frequency can only cone cells respond?
20Hz
Which of the following has the highest lipid content?
a. Retina
b. Choroid
c. Lens
d. Cornea
Retina - contains about 20% lipid, mainly phospholipid - most likely used in retinal / rhodopsin cycle
Which of the following is not a characteristic of trabecular meshwork cells?
a. High levels of microtubules
b. Active phagocytic properties
c. High concentrations of actin
d. Low levels of microtubules
d. Low levels of microtubules
How wide are desmosomes?
20nm
What is the difference between a desmosome and an adherens junction?
Both are cell-cell anchoring junctions. Desmosomes connect intermediate filaments in both cells. Adherens junctions connect actin filaments in both cells.
Which cytokine is involved in eosinophil activation?
IL-5
Which vitamins act as free radical scavengers?
Vitamins A and E
Which of the following is not mediated by histamine H1 receptors?
- CNS depression
- Smooth muscle contraction
- Increased vascular permeability
- Increased pepsin production
- Increased pepsin production is mediated by H2 receptors.
In the blood-retinal barrier, what size molecules cannot pass through the retinal vessels?
> 20 000 Da
What types of retinal emboli are Hollenhorst emboli?
Cholesterol
What two dyes would a corneal specimen from someone with Avellino dystrophy stain for?
Avellino dystrophy = lattice + granular dystrophy
Hence: amyloid (Congo red) + hyaline (Masson trichome)
Is measles virus an RNA or DNA virus?
What about adenovirus?
Measles: RNA virus.
Adenovirus: DNA virus
Are autoclaves effective in destroying bacterial spores?
Yes
What hypersensitivity type is ocular circatricial pemphigoid?
Type 2
What is the trigger for the classical and alternative complement pathways?
Classical: antibody-antigen complexes
Alternative: cell walls of G- bacteria
What cells in the neuroretina are derived from the outer and inner neuroblastic layers? 3 each.
Outer neuroblastic layer:
- Photoreceptors, bipolar cells, horizontal cells
Inner neuroblastic layer:
- Amacrine cells
- Ganglion cells
- Müller cells
Zonules are derived from which stage of vitreous development?
Tertiary
At what age are cones fully developed?
6 months after birth
At what age does the eyeball reach its final size?
8 years
What is the most common ocular complication of maternal rubella in the first trimester?
Cataract (bilateral in 75% of cases)
Congenital rubella syndrome: Eye abnormalities, sensorineural deafness and heart defects (PDA, pulmonary artery stenosis)
What is the most common ocular complication of maternal mumps?
Dacroadenitis
Describe the image formed by a prism.
Virtual, erect and displaced towards the apex of the prism.
Barrel effect and pincushion effect: Which is caused by which sort of lens?
Barrel effect: Caused by convex lenses
Pincushion effect: Caused by concave lenses
What is the dioptric power required for contact lenses for a hypermetrope who usually wears glasses of +5.0D power? (Back vertex power = 1.5mm)
F2 = F1 / (1 - dF1)
Lens is moving towards the eye so sign of d is positive i.e. 0.015m.
F2 = 5 / (1 - (0.015)(5))
= 5 / 0.975
= 5.4
What is the SRK formula and what range of axial lengths is it accurate for?
IOL power required for emmetropia = A (constant) - 2.5 (axial length in mm) - 0.9 (keratometry reading in dioptres).
Valid for axial lengths between 22 and 24.5mm, after which SRK2 or other formulae can be used
Does keratoconus cause axial or refractive myopia?
Refractive myopia (increases the refractive power of the cornea)
With a normal distribution, what percentage of data is within 1, 2 and 3 standard deviations of the mean?
68.3%, 95.5%, 99.8%
How many cranial bones are there? How many facial?
How many of each are paired?
Cranial: 8, 2 paired
Facial: 14, only 2 unpaired
What compounds were shown to reduce AMD progression in the AREDS trial?
Vit C, Vit E
Zinc
Beta-carotene
A closed head injury is most likely to damage which nerve?
CN4 (longest intracranial course)
IS PAX6 linked aniridia AR or AD inheritance?
Autosomal dominant
Femtosecond laser assisted cataract surgery: what are the advantages over traditional phacoemulsification?
- Capsulorhexis is more accurate and reproducible with FLACS
- Likewise for corneal incisions
- Lens fragmentation can be done with reduced instrumentation and power
By what means does uveal melanoma spread?
Haematogenous (rich blood supply to uvea)
Is the Prentice position usually used to specify glass or plastic lenses?
Glass
A crown glass prism with apex angle of 4 degrees is has what minimum angle of deviation?
2 degrees
When treating heterotropia with prisms, which direction should the apex of the prism point?
Apex should point towards direction of deviation
How many prism dioptres can be incorporated into CORNEAL contact lenses?
3 dioptres (6 dioptres for scleral contact lenses)
Can horizontal strabismus be corrected with corneal contact lenses?
No - the prism weights the contact lens so it is always at the bottom. Thus, corneal contact lenses can only be used to correct vertical tropias
What sort of lenses are used in:
- Galilean telescope
- Compound microscope / astronomical telescope
- Loupe
Galilean: + -
Compound: + +
Loupe: +
What is thermokeratoplasty used to treat?
Refractive surgery for hyperopia - cornea is burned and scar tissue causes contraction and steepening of cornea
Silicone oil in (a) phakic (b) aphakic Gas fill in (c) phakic (d) aphakic eyes, what is the ametropia caused in each case?
(a) Silicone oil in phakic eye: Hypermetropia. High RI of silicone oil means light rays diverge from lens to silicone oil.
(b) Silicone oil in aphakic eye: Myopia. No lens present. Curved surface of silicone oil bubble acts as strong converging lens.
(c) Gas bubble in phakic eye: Myopia. Low RI of gas increases converging power of lens
(d) Gas bubble in aphakic eye: Hypermetropia. No lens present and light is not converged by vitreous as vitreous is removed.
If two base out prisms are stacked, will the prism powers summate?
No, as the light entering the second prism will be at the wrong angle (not the position of minimum deviation).
However, perpendicular prisms can be stacked.
When prescribing prisms, are they usually incorporated into one lens only or split across both?
Split across both lenses
Is the image formed by a thin concave lens laterally inverted?
No. It is virtual, erect, diminished and located between F2 and the lens.
A convex lens decentred superiorly results in what sort of prism?
Base-up
Is the base curve of a cylindrical lens the meridian with minimum or maximum curvature?
Minimum curvature
When a convex lens is placed over a cross and moved side to side, is the direction of movement with or against?
Against (similar to retinoscopy rules)
In the Duochrome test, does a myope see the red or green background more clearly?
Red background
Manifest vs latent hypermetropia?
Manifest: Equivalent to the strongest convex lens correction accepted for clear distance vision
Latent: Residual hypermetropia which is involuntarily corrected for by ciliary tone and accommodation
If an emmetropic person has 3D of accommodation remaining, what presbyopic correction do they need to read clearly at 20cm?
20cm: 5D of accommodation necessary.
1/3 of amplitude of accommodation should be held in reserve for comfortable near vision (1D in this patient).
Therefore, this patient will need 6D of accommodative power in total –> 3D of correction.
Does the Stiles-Crawford effect affect rods or cones?
Cones only
What do the primitive dorsal and ventral ophthalmic arteries become?
Dorsal - ophthalmic artery proper
Ventral - nasal long posterior ciliary artery
Most common ocular abnormality with maternal rubella in first trimester?
Cataract
Does CN3 run medially or laterally to the posterior communicating artery?
Laterally.
Emerges from ventral midbrain between the posterior communicating artery and the superior cerebellar artery
Which nerve is relatively protected with cavernous sinus lesions?
CN6 as it is protected by the internal carotid.
The SOF lies between the roof and medial wall of the orbit - true or false?
False - it lies between the roof and lateral wall
Roundworm associated with Chrysops horseflies / deerflies
Loa loa (endemic in W Africa)
Does the cornea have a subepithelial nerve plexus?
Yes, and a sub-basal nerve plexus as well.
Innervation is CN V1 via long ciliary nerves.
Does Bowman’s layer contain Type 2 collagen?
No. Mainly contains types 1, 3, 5, 6
Are corneal endothelial cells highly interdigitated?
Yes - many gap junctions and cell-cell transport
The sclera is thinnest posteriorly, true or false?
False. It is thickest posteriorly (1mm) and thinnest at the insertions of the EOMs
Does the sclera contain more or less GAGs than the cornea?
Less - almost half the amount and chondroitin sulfate rather than keratan sulfate
What gestational age is aqueous produced from?
7th month - when angle forms
At what gestational age does the ciliary body start to develop?
3rd month (week 12)
When does the lens placode form?
Day 27
When do the sphincter and dilator pupillae muscles form? Which one first?
Sphincter before dilator (14 weeks and 6 months respectively)
Which gene localises to the future ciliary body / iris in the embryo?
Hox 7.1
What order neurones does the optic nerve contain?
Second order neurones (GCs)
First order are bipolar cells
When does the choroidal fissure begin to close?
Week 6; complete by week 7
Malleus, incus, stapes: which pharyngeal arches?
Malleus and incus: First pharyngeal arch
Stapes: 2nd pharyngeal arch
What is the main collagen in the vitreous?
Type 2
Which margin of the orbital rim is thickest?
Lateral
Does the trigeminal nucleus form part of the midbrain?
Yes - the mesencephalic nucleus extends into the midbrain
Does lipofuscin accumulate intra or extracellularly?
Intracellularly in RPE cells
Does retinoblastoma metastasise?
Yes - mainly via orbital nerve, but also through sclera
How much does the LPS raise the lid by?
12-13mm
How thick is the tear film?
10um
State the mechanisms of inheritance of oculocutaneous albinism and ocular albinism.
Oculocutaneous: Autosomal recessive
Ocular: X-linked recessive
Where is the superior salivatory nucleus located?
Pons (just above pontomedullary junction)
Secretory IgA is highest in concentration in non-stimulated basal tears: true or false?
True
The majority of retinal ganglion cells encode information via which pathway: magnocellular or parvocellular?
Parvocellular (90% of axons!)
What are transitions and transversions in DNA mutations?
Transitions: purine -> purine or pyrimidine -> pyrimidine
Transversions: one type is replaced by another
Can first and second order Horners syndrome be distinguished pharmacologically?
No, only third order reacts differently
What HLA subtype is associated with MS?
HLA-DR2
HLA for birdshot chorioretinopathy?
A29
HLA for Behcet’s
B51
In X-linked dominant inheritance, what percentage of offspring of an affected mother will be affected?
50% (affects boys and girls equally)
Which parasympathetic ganglion supplies the conjunctiva?
Pterygopalatine
Is thioglycollate broth used for only anaerobic bacteria?
No, is a general all-purpose medium
In ERGs, is the b wave generated by outer or inner retinal element?
Inner (bipolar and Muller cells)
Which 2 adrenergic receptors are dominant in the ciliary body epithelium?
apla-2 and beta-2
Patient with:
- L inferior rectus, inferior oblique and medial rectus weakness
- R superior rectus weakness
- Bilateral ptosis
Where is the lesion?
Left oculomotor nucleus.
3 groups of subnuclei:
- Ipsilateral IR, MR, IO innervation
- Contralateral SR innervation
- Bilateral LPS innervation from central nucleus
What are the 2 most common sites of scleral rupture?
Superonasal limbus (from trauma) Insertion of the recti
What germ layer is the trabecular meshwork derived from?
Mesenchyme / NCC
Is vancomycin effective against G- bacteria?
No (cannot penetrate cell membrane)
In surgery, what anatomical position is marked by the grey line?
Anterior border of the tarsal plate
Rate of CSF production and total CSF volume
550ml produced / day
Total vol 150ml
Which bones in the orbit do not derive purely from membranous ossification?
Sphenoid and ethmoid (skull base) derive from cartilaginous ossification
Pelli-Robson and Hardy-Rand-Rittler: which one does not assess colour vision?
Pelli-Robson - assesses contrast sensitivity
What sort of image is produced by a Hruby lens?
Virtual, erect and diminished image is formed within the vitreous.
Is HLA-B27 associated uveitis granulomatous or non-granulomatous?
Non-granulomatous
What is the inheritance pattern of Gorlin-Goltz syndrome?
Autosomal dominant
Describe the % hydration of the cornea and sclera
Cornea: 80% hydrated
Sclera: 70% hydrated
What is the effect of mydriasis on depth of field and depth of focus?
Decreases both.
What stage of trachoma is characterised by contraction of the palpebral conjunctival stroma?
Stage 4
Effect of acetazolamide on pH and K+
Metabolic acidosis (reduced renal reabsorption of bicarb) but hypokalaemia
What is the primary route of glucose utilisation by the corneal endothelium?
Anaerobic glycolysis. (More aerobic glycolysis than the epithelium, but still mostly anaerobic)
The maximal number of axons in the optic nerve is acheived at:
15 weeks gestation. (Nearly 4 million, then gets pruned down to the normal 1.2million by 30wks)
In what part of the nephron does water absorption not take place?
Ascending limb of loop of Henle
What is the horizontal corneal diameter at birth
10mm (compared to 11.7 in the adult)
