EyeDocs Flashcards
What does Ethylene Oxide gas do in sterilisation
Ethylene oxide gas is useful for heat sensitive instruments. Irradiation and chemical germicides are other techniques of sterilisation
Which condition is characterised by corneal epithelial cyst formation
Corneal epithelial microcyst formation due to abnormalities in the structure and function of corneal epithelial basement membrane occurs in Cogan’s (map-dot-fingerprint) dystrophy
What does epinephrine cause in the eye
Lowers IOP
Which mutation is MOST likely to cause premature termination of translation:
A single base insertion in the exon or coding region would cause a frameshift mutation and usually leads to premature termination of translation
What does a mutation in the promoter region of DNA translation do?
most likely alter gene regulation
What does a stroke of the anterior choroidal/lateral striate arteries cause?
stroke of the anterior choroidal or lateral striate arteries which supply the optic tracts and radiations would cause a homonomous hemianopia.
Where does the short ciliary nerve arise from?
The short ciliary nerve arises from the ciliary ganglion and carries sensory (from the nasociliary), sympathetic and parasympathetic fibres (predominantly from the third nerve but also from the seventh). The long ciliary nerve, which passes through the choroid and transmits sensory fibres to the cornea, iris and ciliary body (as well as sympathetic fibres to the dilator pupillae muscle) is a branch of the nasociliary nerve, itself a branch of the ophthalmic nerve.
Features of lasers
All laser beams are
monochromatic (same frequency),
coherent (phase-synchronised), and
collimated (same direction).
They do not have to be polarised.
What are features of optical defects due to the prismatic effect at the edge of a convex lens?
Pincushion effect
Spherical aberration
Jack in the box
Ring scotoma
A barrel effect is caused by the prismatic effects of a strong concave lens, while a pin-cushion effect is the inverse optical phenomenon that occurs in a strong convex lens
What are the rules of refracting powers of a curved surface
determined by the principles of Snell’s law
measured in diopters
equal to the difference in refractive indices of the media divided by the radius of curvature
the power is directly proportional to the difference in refractive indices but indirectly proportional to the radius of curvature of the surface
What does a right frontal lobe lesion cause in terms of gaze paresis?
Right frontal lobe lesion will cause left hemiparesis and deviation of eyes to the right side, with gaze paresis to the left
What are the high concentration constituents of aqueous humour compared to plasma?
The aqueous humour has a lower concentration of virtually all constituents compared to the plasma, with the exception of lactate, ascorbate and chloride. It therefore has a lower protein, glucose, sodium, potassium and bicarbonate concentrations
How is the basal columnar layer of the corneal epithelium attached to its basal lamina by?
hemidesmosomes
What does the synoptophore do?
measure all aspects of binocular single vision including simultaneous perception, fusion (including range of fusion) and stereopsis
It can also measure the degree of misalignment for horizontal, vertical and torsional misalignments in all directions of gaze. It can detect suppression and abnormal retinal correspondence (ARC).
How does the synophtophore measure ARC
the objective angle (OA) and subjective angle (SA) are measured, which gives the angle of anomaly (AOA).
AOA = OA - SA
In normal retinal correspondence (NRC), the SA is equal to OA and the AOA will be zero.
In unharmonious ARC, the SA will be less than the OA (but the SA will not be zero)
In harmonious ARC, the SA will be zero, so the AOA will be equal to the OA
Where does the third cranial nerve arise from?
The third cranial nerve arises from the brainstem between the posterior cerebral artery and the superior cerebellar artery
What is Actinomyces most likely to cause?
Actinomyces is a Gram-positive filament which is a common cause of canaliculitis and dacrocystitis
What does Coagulase do?
coagulase facilitates deposition of a protective fibrin coat on the bacteria
Where is the sclera thinnest?
At the insertion of the recti
Where is the occulomotor nerve nucleus found in the midbrain?
periaqueductal grey matter in the midbrain
What medications may be associated with the induction or aggravation of angle-closure glaucoma
Both mydriatics and miotics can precipitate angle-closure in eyes with shallow anterior chambers. This is true for both topical medications and systemic drugs that affect the pupil.
What is the cause of acute viral haemorrhagic conjunctivitis
Acute haemorrhagic conjunctivitis is classically caused by picornaviruses including the Coxsackie group A24 and enterovirus E70. Adenoviral conjunctivitis can also cause haemorrhage
Which aminoglycoside is most likely to induce an allergic conjunctivitis response
Neomycin
Which immunoglobulin class has the highest individual molecular weight?
IgM is a pentamer, consisting of five immunoglobulin units, making it the largest of the antibody classes
How does the corneal epithelium use most of its glucose?
The corneal epithelium utilises most of its glucose (85%) for the production of ATP via glycolysis anaerobically with lactate production. A small proportion of glucose is metabolized aerobically via the Krebb’s cycle. Some glucose is also diverted to the pentose phosphate pathway, which is important for the production of antioxidants such as glutathione and ascorbic acid. The production of sorbitol from glucose is a minor pathway and only occurs to a significant degree in hyperglycemic states.
Structures in the eye originating from Neuroectoderm
retina - neurosensory and RPE
epithelial lining of iris and ciliary body
optic nerves
Structures in the eye originating from Surface Ectoderm
lens
corneal epithelium
conjunctival epithelium
lacrimal gland
nasolacrimal system
Meibomian glands
Structures in the eye originating from Neural crest
sclera
iris stroma
cornea: stroma and endothelium
TM and Schlemm’s canal
extraocular muscle
ciliary muscle
connective tissue and bony structure of the orbit
Structures in the eye originating from Mesoderm
extraocular muscles
endothelial lining of blood vessels of the eye
blood vessels in sclera and choroid
sclera
vitreous
suspensory fibres
angle outflow apparatus
What is the rate of basal tear production?
Basal tear production is 1.2 microlitres per minute but a massive increase is possible through reflex secretion induced by mechanical and psychological stimuli.
Innervation and blood supply to ciliary body
it is supplied with sympathetic innervation which synapses in the superior cervical ganglion
it is supplied with blood from both the long posterior ciliary arteries and the anterior ciliary arteries
it is supplied with parasympathetic innervation via the short ciliary nerves
What does chloroquine bind to in the retina
It is bound to the melanin in the retinal pigment epithelium which is believed to be the reason for its toxicity. It causes Bull’s eye maculopathy which may progress despite stopping the medication
Definition of the p-value
The p value is the probability of obtaining a test statistic result at least as extreme as the one that was actually observed, assuming that the null hypothesis is true.
What is the commonest protozoal parasite to affect the eye
Toxoplasma Gondii
What does sabroud agar grow
Fungus
What does Thayer Martin grow
Gonococcus
What does Lowenstein Jensen grow
TB
What does non-nutrient e.coli-enriched agar grow
Acanthamoeba
What are Dalen Fuch’s nodules
an accumulation of macrophages in the retinal pigment epithelium. The condition can lead to exudative retinal detachment secondary to severe inflammation, with consequent hypotony and phthisis bulbi.
Where is the Outer capillary plexus of the retina found?
INL
Stages of acute inflammation
there is transient vasoconstriction, which is followed by vasodilatation;
there is relative stasis of blood and retraction of the endothelial cells making the blood vessels more permeable.
Neutrophils are the first cells seen in the extracellular space. Histamine is an important mediator that causes vasodilatation and increased vascular permeability
Where is the vascular abnormality in Coats disease found?
the result of an abnormal endothelium in arterioles and venules. This causes massive leakage of lipid-rich plasma into the retina and the subretinal space.
What substrate does the pentose phosphate pathway produce?
converts glucose-6-phosphate to ribose with the production of NADPH (not NADP). Ribose is important for the synthesis of nucleic acids (DNA and RNA) while NADPH is important for use in reductive biosynthetic reactions such as fatty acid synthesis. The pathway also permits gluconeogenesis, the production of glucose from unrelated precursors
Optic nerve head RNFL blood supply?
branches of the central retinal artery
Optic nerve head prelaminar region blood supply?
capillaries of the short posterior ciliary arteries
Optic nerve head lamina cribrosa region blood supply?
vessels that come directly from the short posterior ciliary arteries to form a dense plexus in the lamina.
Optic nerve head retrolaminar region blood supply?
ciliary and retinal circulations, with the former coming from recurrent pial vessels, while the central retinal artery provides centripetal branches from the pial region
Corneal tissue energy consumption from highest to lowest?
Endothelium, epithelium, stroma
What is the largest cranial nerve?
Trigeminal nerve
Type 1 vs Type 2 HIV infection
Type I HIV occurs primarily in urban centres in the USA and Europe and is more common in homosexuals and intravenous drug abusers. Type 2 is more common in Africa and is mainly heterosexually transmitted
Features of the superior orbital fissure
it is the largest communication between the orbit and the cranial cavities
is approximately 22mm long
it is bound by the lesser and greater wings of sphenoid
comma-shaped, being wider at its medial end than laterally.
Which chlamydia serotypes cause Trachoma?
Serotypes A, B, and C cause trachoma
What are the strong points of vitreo-retinal adhesion?
major retinal blood vessels
the edge of retinal scars
the edge of lattice retinal degeneration
the vitreous base
What are the strong points of choroido scleral adhesion?
Vortex veins
Blood supply to lateral geniculate nucleus
dual blood supply from the anterior choroidal artery (a branch of the internal carotid artery) and from the lateral posterior choroidal artery (a branch of the posterior cerebral artery)
Most common corneal dystrophy
lattice, followed by granular
What does amyloid stain with?
Congo red
crystal violet
thioflavin T
How to calculate NNT
NNT is defined as number needed to treat to prevent 1 event.
NNT = 100/ARR (ARR= Absolute risk reduction)
ARR = |CER - EER|
Where:
CER = control group event rate
EER = experimental group event rate
Features of the left recurrent laryngeal nerve
The left recurrent laryngeal nerve arises from the vagus nerve as it crosses the arch of the aorta. It ascends in the groove between the trachea and esophagus and lies anterior to the sympathetic trunk. It also has a sensory component that supplies part of the mucous membrane of the larynx and trachea. It supplies all the laryngeal muscles except the cricothyroid muscle which is supplied by the external laryngeal nerve
What do the variable regions of the immunoglobulins correspond to?
Amino termini of both the light and heavy chains.
Formula for angular magnification
Angular magnification of a magnifying lens or loupe = 0.25/f = 0.25 x D
What is the absolute hypermetropia?
the least amount of plus lenses needed for clear distance vision without cycloplegia
What is the manifest hypermetropia?
the most plus that can be tolerated without blurring of vision and without cycloplegia
What is the facultative hypermetropia?
the difference between the absolute and the manifest hypermetropia
What is the latent hypermetropia?
the difference between the manifest hypermetropia and hypermetropia measured with cycloplegia
Features of exotoxins
Exotoxins are proteins released by Gram-positive bacteria and produce specific effects at sites distant to their release. They are highly toxic, antigenic and are readily destroyed by heat.
What is a contiguous gene syndrome?
caused by minute deletions of a part of a chromosome causing a distinct syndrome. These are not usually detectable by routine chromosome studies and require specialised tests for confirmation. Fluorescence in situ hybridisation (FISH) testing is typically used to confirm the diagnosis
Conditions with Mitochondrial inheritance
Lebers hereditary optic atrophy (LHON)
mitochondrial encephalopathy, lactic acidosis, and stroke (MELAS)
myoclonus epilepsy associated with ragged-red fibers (MERRF)
Kearns-Sayre syndrome (KSS)
Pearson syndrome
some types of diabetes and deafness
Which chromosome are blue cones found on
Chromosome 7
Which chromosome are red and green cones found on
X chromosome
What does the Worth 4 dot test test at distance
When the Worth 4-dot is performed at distance, central retinal elements are stimulated, and central fusion is evaluated
What does the Worth 4 dot test test at near
When performed at near, more peripheral fusion processes are tested.
What is a type 1 error
A type-1 or alpha error occurs when the null hypothesis is falsely rejected (false positive). In other words, a significant difference is found between two drugs when, in actual fact, there is none, and instead the result has occurred by chance. A p value of 0.05 indicates there is a probability of 5/100 (1 in 20) that the result may have occurred by chance
What is a type 2 error
A type-2 or beta error occurs when the null hypothesis is wrongly accepted, ie a false-negative. For example, in a clinical trial, a type-2 error has occurred when the study fails to detect a significant difference between the two drugs on trial when in fact there is one. This can happen if the sample size is too small. Studies therefore have to have adequate power to find a difference if one exists. Formulae are available to help work out the minimal sample size required.
What is the age of greatest progression of keratoconus
Second decade
How do restriction endonucleases work
by breaking the sugar-phosphate backbones of the DNA.
What factors influence the diffusion coefficient of a drug
lipid solubility, ionization and molecular size.
What does the confidence interval tell us
A confidence interval which is narrow emphasizes the significance of a result, but it is the p value which describes significance not the confidence interval
Where does the geniculocalcarine tracts or optic tracts pass through
pass anteriorly to form a loop called the loop of Meyer (not Miller) which passes through the parietal and temporal lobes. Fibres from the inferior retina (corresponding to the superior visual field) take a wider course passing deeper into the temporal lobe than fibres from the superior retina. Fibres from the macula tend to have the straightest course.
Where does the lateral geniculate nucleus send a large proportion of its fibres to?
The primary role of the lateral geniculate nucleus is a relay station for the conscious pathway of visual perception. To this end, it sends the majority of its fibres to the visual cortex, also called area 17. It also has connections to the superior colliculus, reticular formation and hypothalamus.
Which enzymes are involved in translation
Translation is the production of an amino acid sequence from mRNA in the cytoplasm. It is controlled by 2 main enzymes: aminoacyl-tRNA synthetase (which helps join tRNA to its specific amino acid) and by peptidyl transferase which involves the uncoupling of the tRNA from the amino acid and joining of the amino acid to the growing polypeptide chain
How are drugs made to penetrate the cornea
For drugs to penetrate the cornea, they must be biphasic - i.e. both hydrophilic and hydrophobic. To achieve this, steroid molecules such as prednisolone, dexamethasone and rimoxalone are combined with other compounds (usually bases) such as phosphate and acetate. Acetate compounds penetrate the cornea best, but they must be in suspension form, meaning patients must remember to shake the bottle before administration. Alcohol is the next best penetrant, followed by phosphate. The advantage of these latter varieties is that they can be made into solutions, which are easier to apply.
Direct vs indirect gonioscopy
With direct gonioscopy, the angle is visualized directly through the contact lens; while with indirect gonioscopy, light rays are reflected by a mirror in the contact lens.
Examples of direct gonioscopy lenses
Koeppe, Richardson, Barkan, Wurst and Swan-Jacob lenses.
Examples of indirect gonioscopy lenses
Goldmann, Zeiss, Posner and Sussman lenses.
Histological ‘body’ found in Optic nerve meningioma
Psammoma bodies
Ehler danlos collagen type deformity
defective Type 1 (or Type 3) collagen
Stickler’s syndrome collagen type deformity
defective Type 2 (or Type 9) collagen
Alport syndrome collagen type deformity
defective Type 4 collagen
Relations of the optic chiasm
inferior: diaphragma sellae
superior: lamina terminalis
anterior: anterior cerebra and communicating arteries
posterior: pituitary stalk
lateral: internal carotid artery
Where is the widest dimension of the orbit
1cm posterior to the anterior orbital rim
What is Avelino dystrophy
Amyloid may also be deposited in granular type 2 (also known as Avellino dystrophy, which can be thought of as a mix of granular and lattice dystrophy with deposits of hyaline and amyloid). In granular type 1 dystrophy there are only deposits of hyaline.
Where does the 6th nerve exit the brainstem
at the junction of the pons and medulla. It runs upward in the pontine cistern. It pierces the dura and at the tip of the petrous temporal bone makes a sharp turn forward to enter the cavernous sinus.
Main glycosaminoglycan of the cornea
Keratan and dermatan sulphate
Where do saccades originate from
Saccades are controlled by the contralateral frontal lobe.
Where do pursuits originate from
Pursuit is controlled by the ipsilateral parietal lobe
Where does the arachnoid villi drain CSF into
The superior sagittal sinus drains the cerebral bridging veins and, through the arachnoid villi, the cerebrospinal fluid.
Granulomatous vs non granulomatous keratic precipitates
Granulomatous (mutton fat) keratic precipitates (KPs) are predominantly composed of macrophages while non-granulomatous KP’s are composed of lymphocytes and polymorphonuclear leukocytes.
Mydriatic drug action durations
Tropicamide: duration 6 hours
Cyclopentolate: duration 24 hours
Homatropine: duration 2 days
Atropine: duration up to 2 weeks
What is the lens capsule made out of
Its extracellular matrix composition includes predominantly type IV collagen and laminin
Derived from surface ectoderm
Where is the standard reference plane taken in Heidelberg retinal topography (HRT) of the optic disc?
50 um below the optic nerve head boundary line at the temporal disc edge along the horizontal midline
This location is taken as the standard default reference plane because it corresponds to the centre of the papillomacular bundle of the RNFL. This papillomacular bundle is usually preserved until late in glaucoma, so it would be expected to have a stable thickness over time.
Examples of non parametric statistical tests
Wilcoxon signed-rank
Chi-squared
Mann-Whitney U test
What is the standard error of the mean (SEM)
If we were to take several samples from the same population, all would result in normal distribution curves, but would be slightly different from each other. Each mean would be scattered around the true population mean. The standard error of the mean is a measure of this scatter, i.e. how accurate is the sample mean as an estimate of the true population mean.
Note, SEM = Standard deviation/square root of sample size
What is the Purkinje shift
a shift in peak spectral sensitivity, from 555 nm to 505 nm, with dark adaptation.
What are ocular manifestations of Sturge Weber syndrome
choroidal haemangioma
glaucoma due to vascular proliferation in the angle
Normal EOG response
The normal ratio is more than 180%.
What visual field defect does a toxic nutritional neuropathy produce
A bilateral centrocoecal scotoma
Static vs kinetic perimetry
In static perimetry (such as the Humphrey), the stimulus is of variable intensity and is kept stationary (static) until it is noticed by the patient. The Goldmann field is a form of kinetic perimetry, with a moving target. Baring of the blind spot and generalised constriction are not very specific and can be produced by miosis, uncorrected refractive error, aging, and cataract
What is Pannum fusional area
Panum’s fusional area indicates the degree of retinal disparity that still produces binocular single vision, whereas fusional amplitudes indicate the degrees of retinal disparity outside Panum’s fusional area that can be overcome by realignment of the eyes (motor fusion)
Where is the canal of Petit found
between the orbiculo-posterocapsular bundle and the anterior vitreous cortex.
Where is the canal of Hannover found
between the orbiculo-anterocapsular bundle and the orbiculo-posterocapsular bundle.
Which interleukin does cyclosporin suppress
IL-2
Synaptic terminals of rods and cones
The synaptic terminals of the cones are called pedicles while those of the rod are termed spherules. They synapse with bipolar and horizontal cells
Where are the 5 A scan peaks in the eye
corneal surface
lens anterior surface
lens posterior surface
ILM of the retina
sclera
What is the order of increasing maturity of cells seen in Retinoblastoma
In order of increasing maturity: Homer-Wright rosettes, neuroblasts, Flexner-Wintersteiner rosettes, early retinal cell, fleurettes, immature photoreceptor cells. The type of cells are not a prognostic indicator.
RB cells derive from neuro-epithelial cells and have the potential to differentiate into photoreceptors or Muller cells.
What structures are involved in vertical eye movements
The supranuclear control of vertical saccades originates in the frontal eye fields or in the superior colliculus. They project to neurons in the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) and on to the nuclei of cranial nerve III and IV. The interstitial nucleus of Cajal is involved with vertical pursuit control.
Which structures control horizontal eye movements
PPRF The paramedian pontine reticular formation (PPRF) controls horizontal eye movements.
Effect of silicone oil on phakik vs aphakik patient
Silicone oil in an aphakic eye causes a myopic shift, while silicone oil in a phakic eye cause a hyperopic shift.
Features of endotoxins
Endotoxins are lipopolysaccharides derived from the cell wall of gram negative bacteria. They are heat stable unlike exotoxins. They are non-antigenic as against exotoxin. They cause septicemia and fever and activate the alternative pathway (non-antibody mediated) of the complement system.
Genetic imprinting vs genetic anticipation
Genetic imprinting is the phenomenon of differential gene expression depending on the sex of the parent who transmitted it.
The number of trinucleotide repeats increases with successive generations leading to more severe disease; this is called genetic anticipation.
Three pathways of complement activation
Classic
Alternative
Lectin
How to calculate the false positive rate
100- specificity
Which cytokine is secreted by Th2 cell
IL4
Origin of the IO Muscle
The inferior oblique muscle has its origin on the maxillary bone just posterior to the inferior medial orbital rim and lateral to the nasolacrimal canal.
What Bacteria are capable of establishing infection with intact epithelium
Haemophilus
Neisseria spp.
Corynebacterium spp.
Listeria spp.
What are the core proteins of gap junctions
Connexins
What are the core proteins of tight junctions
Occludin, claudins and junctional adhesion molecules (JAM) are constituent proteins of tight junctions.
Lockwood ligaments components
the sheath of inferior rectus
the medial check ligament
the lateral check ligament
sheath of inferior oblique
Examples of mitochondrial inherited conditions
LHON
Kearns Sayre
CPEO
Characteristics of IgG
(80% of total immunoglobulin)
activates the classical complement pathway; transferred across the placenta; monomeric; important immunoglobulin in the secondary immune response
Characteristics of IgM
(6% of total Ig)
activates the classical complement pathway +++; IgM fixes complement most effectively; pentameric structure; present on the membranes of B cells; mostly confined to the intravascular space; important in the primary immune response.
Characteristics of IgA
(10-15 % of total serum Ig)
is the predominant immunoglobulin in the external secretions; activates the alternative complement pathway; secretory IgA dimeric form with J chain; occasionally exists as a tetramer; IgA is very important for mucosal immunity.
Characteristics of IgD
(<1% of total serum Ig)
B cell surface Ig; possible role in B/T cell activation.
Characteristics of IgE
(0.001% of total serum Ig)
binds with high affinity to mast cells and are involved in active immunity against helminth parasites.
Jaw opening muscles
lateral pterygoid and mylohyoid.
Jaw closing muscles
medial pterygoid, temporalis and masseter.
How to correct WTR Astigmatism
With-the-rule astigmatism occurs when the vertical meridian is steepest; it is corrected with a plus cylinder at 90, or a minus cylinder at 180
How to correct ATR Astigmatism
Against-the-rule astigmatism occurs when the horizontal merdian is steepest; it is corrected by a plus cylinder at 180 or a minus cylinder at 90
Basal cell carcinoma histology
characterised by clusters of darkly staining basaloid cells with a palisade arrangement of nuclei at the periphery of the clusters.
What is glycolysis
Glycolysis is the conversion of glucose to two molecules of pyruvate with the production of two NADH molecules and two ATP molecules. Glycolysis occurs in the cytoplasm and does not require oxygen
What are normal fusional vergence
Vertical: 2-3 PD
Torsional: 2-3 degrees
Convergence: 15-20 PD distance, 25 PD near
Divergence: 6-10 PD distance, 9-12PD near
What is a choristoma
comprised of normal tissue in an abnormal location (e.g. a dermoid).
What is a hamartoma
comprised of tissue elements normally found at that site
Which topical IOP-lowering agent should be used with caution in corneal endothelial dysfunction?
Carbonic-anhydrase inhibitors can affect the corneal endothelial pump mechanism, and should therefore be used in caution in patients with corneal endothelial dysfunction.
The proto-oncogene RET causes which thyroid cancer?
medullary
What is the power of a study
the probability of not producing a type II error; in other words the probability of NOT accepting a false null hypothesis; or in other words the ability of a study to detect a significant difference when a significant difference is present.
What is the angle of deviation of a prism dependent on?
the refractive index of the prism
the refractive angle of the prism
the angle of incidence of light
By how many degrees is the fovea displaced from the optic nerve?
The blind spot on visual fields (produced by the optic nerve) is 15 degrees from fixation, corresponding with the displacement of the optic nerve from the fovea.
Where do hard exudates occur?
Hard exudates occur in the outer plexiform layer. they contain foamy macrophages with lipid in their cytoplasm
Where does CN 3 exit the brainstem
Interpeduncular fossa
Where does CN 4 exit the brainstem
inferior to inferior colliculus (dorsal)
Where does CN 5 exit the brainstem
over ventrolateral pons
Where does CN 6 exit the brainstem
junction of pons and pyramid of medulla
Where does CN 7,8 exit the brainstem
cerebellopontine angle
Which embryological layer does the pitutary gland originate from
Neuroectoderm
How many cell layers of the LGN?
6
How long is a cone photoreceptor
cone is 60-75 micrometers.
How long is a rod photoreceptor
100-120 micrometers long
Which extraocular muscle are supplied by ipsilateral vs contralateral brainstem nuclei
All of the extraocular muscles are supplied by ipsilateral nuclei except the superior rectus and the superior oblique, which are contralateral.
Also note that the levator muscle is innervated bilaterally by a single, unpaired nucleus.
Leber Congenital Amaurosis ERG
Leber’s congenital amaurosis is a disorder of congenital blindness that often presents with a normal appearing fundus in the neonatal period. However, an ERG done at this time will show a severely attenuated or extinguished ERG
Which organ does accessory vs reflex tearing
Accessory: Glands in the conjunctiva
Reflex: Lacrimal gland
Which conditions can cause a positive VDRL test
syphilis
rheumatoid arthritis
systemic lupus erythematosus
antiphospholipid syndrome
a,b,c waves of ERG Correspondence
The a-wave originates from the photoreceptors, the b-wave from the bipolar cells and the c-wave from the RPE.
In order to truly isolate cone function, it is necessary to present a light stimulus as a flicker-flash at what minimum frequency?
Rods can respond to flickering stimuli with rates up to 20 Hz. Only cones can respond at higher frequencies, with a maximum of approximately 70 Hz.
Is HPV a DNA/RNA virus
DNA
Can a Hess Chart be used to measure torsion
No. Only vertical and horizontal squints
Features of Neuromyelitis Optica (Devic’s Disease)
optic neuritis (often severe, and may be bilateral)
transverse myelitis (T-2 lesions on MRI extending over 4 contiguous vertebral sections)
positive for anti-aquaporin 4 antibodies
Which extraocular muscle receives a blood supply from the lacrimal artery in addition to its supply from direct branches of the ophthalmic artery:
All extraocular muscles are supplied directly by branches of the ophthalmic artery called the anterior ciliary arteries. These also supply the anterior segment of the eye via the episcleral arterial circle and the major arterial circle of the iris. Usually, each rectus muscle receives 2 anterior ciliary arteries, with the exception of the lateral rectus which receives only one.
Besides direct branches from the ophthalmic artery (as anterior ciliary arteries), some extraocular muscles have auxiliary blood supplies. The lateral rectus muscle is also supplied by the lacrimal artery, a branch of the ophthalmic artery. The inferior rectus and inferior oblique are supplied by the infraorbital artery (a branch of the internal carotid artery).
Normal pH of tears
The normal pH of tears is between 6.5 to 7.5 with a mean of 7.
Pseudotumour vs TED
Pseudotumour unlike TED can and commonly does involve the muscle tendons as well as their insertions, along with the posterior Tenon fascia and sclera. Besides these findings, the two conditions may be virtually indistinguishable on imaging.
Laser choice in patient with Vitreous haemorrhage and PDR
The wavelength of krypton red (646 nm) is best able to penetrate vitreous haemorrhage and deliver the necessary energy to create photocoagulation scars.
What is INO
Failure of adduction in both eyes signifies a bilateral internuclear ophthalmoplegia. This is often accompanied by nystagmus of the abducting eye. The area of the brain affected is the medial longitudinal fascicles in the brain stem which connects the third and sixth nerve nuclei.
Which glaucoma drops are shown to be teratogenic
Prostaglandin analogues, carbonic anhydrase inhibitors and beta-blockers have all been shown in animal studies to have teratogenic effects
Which pharyngeal arch does the maxillary nerve come from
First pharyngeal arch
Tuberculin test indication of active disease
An area of induration >15mm is a strongly positive result and suggests active disease. A weakly positive test is difficult to distinguish active disease from previous exposure or immunization. A negative result usually excludes TB but may occur in comsumptive disease.
What are features of restriction fragment length polymorphisms (RFLP)
RFLPs may be used to diagnose Huntington’s disease. Enzymes from bacteria called restriction endonucleases are used in RFLPs. These are known to cleave at specific sites, resulting in specific fragments of the DNA material being analysed. The relative position of different genes on a chromosome is called ‘linkage’. By using RFLPs, a linkage map may be created when the genes are too close to be seen on microscopy. Tracking of the disease gene through successive generations may be done with RFLPs. Southern blotting is the technique used in RFLP analysis. A difference of more than a million base pairs of DNA would be detectable by microscopy. For differences less than this, RFLPs will be useful.
Examples of gene mutation detection techniques
DNA sequencing and Southern blotting
Examples of gene expression technique
microarray analysis
Relative tissue intensities on MRI
T1: Fat > white matter > gray matter > CSF
T2: CSF > gray matter > white matter > fat
FLAIR: fat > gray matter > white matter > CSF
STIR: CSF = gray matter > white matter > fat
Origin and course of CN3
The 3rd cranial nerve arises in the oculomotor nuclei, located adjacent to the aqueduct of Sylvius. The Edinger-Westphal nucleus is dorsal among these and provides the parasympathetic component of the nerve (pupil). The muscle-controlling nuclei lie ventrally, with unique areas of control for each muscle. The levator palpebrae are innervated bilaterally. Along the brainstem, the fibers pass the medial longitudinal fasciculus, red nucleus, substantia nigra, and medial portion of the cerebral peduncle. From here, they pass between the posterior cerebral and superior cerebellar arteries. Anterior to the cavernous sinus, the nerve crosses the junction of the internal carotid artery and posterior communicating artery. It enters the orbit through the superior orbital fissure. The superior branch innervates the superior rectus and levator palpebrae. The inferior branch innervates all oculomotor muscles apart from the superior oblique and external rectus.
Imaging modality for suspected exacerbation of TED
T2 weighted STIR sequences are best for delineating thyroid activity. T2 allows evaluation of activity in the extraocular muscles while STIR suppresses orbital fat allowing excellent visibility of adjacent structures.
Which nerve runs along the length of the inferior orbital fissure towards the lateral orbital wall:
The zygomatic nerve runs the length of the inferior orbital fissure towards the lateral orbital wall, where it pierces the zygoma as 2 branches: the zygomaticotemporal and zygomaticofacial nerves.
What is the power of a study
The option ‘the probability of rejecting the null hypothesis that the treatments have the same effect’ would become correct if it was extended to say ‘when there is a prespecified treatment difference’, but is incorrect as it stands. Power has to do with statistical significance not clinical significance. Power is often defined as 1 minus the probability of a type-2 error
What is the mechanism of action of edrophonium?
Edrophonium (Tensilon) is a short-acting anti-cholinesterase inhibitor. It prolongs the duration of acetylcholine in the synaptic cleft.
Which corneal dystrophy is a localized form of mucopolysaccharidosis?
Macular dystrophy is an autosomal recessive corneal stromal dystrophy. It is a localised form of mucopolysaccharidosis with mucopolysaccharide granules in the cytoplasm of keratocytes.
The basal lamina of the inner layer of the optic cup differentiates into:
The basal lamina of the inner layer of the optic cup becomes the internal limiting membrane. The basal lamina of the outer layer of the optic cup becomes incorporated into Bruch ‘s membrane.
PORN vs ARN
Progressive outer retinal necrosis (PORN) involves destruction of the outer retina without the accompanying vitritis and vasculitis associated with acute retinal necrosis.
Where does the superior oblique insert on the globe?
The superior oblique inserts on the posterosuperior quadrant of the globe.
Which foramen does the MMA enter the brain through?
The middle meningeal artery enters the skull through the foramen spinosum.
Layers of the choroid
The choroid is composed of 5 layers:
Bruch’s membrane
the choriocapillaris
Sattler’s layer
Haller’s layer
the suprachoroid
Optic nerve length and breakdown
intraocular: 1mm
intraorbital: 30mm
intracanalicular: 6mm
intracranial: 10mm
Which enzyme produces hydrogen peroxide and oxygen from the superoxide radical?
superoxide dismutase
What does the foramen lacerum do?
The foramen lacerum transmits parasympathetic fibres via the greater petrosal nerve, which synapse in the pterygopalatine ganglion.
Lactic acid accumulation in the cornea is MOST likely to manifest as
When the cornea becomes hypoxic (e.g. over-wearing of ill-fitting contact lenses preventing diffusion of oxygen from the tear film) lactate builds up due to increased anaerobic respiration. Only a small amount of lactate is removed via the tears - the majority must diffuse through the stroma and endothelium to the aqueous, causing a build-up in the cornea. This shifts osmotic balance pulling water into the corneal stroma inducing oedema. Lactate transport to the aqueous is facilitated by the H+/lactate pump - this causes increased acidification of the cornea; with secondary egress of K+ and resultant cell shrinkage and apoptosis. If acidification involves keratocytes, cellular damage can affect collagen production resulting in scar formation.
When do the majority of flap folds occur after laser-assisted in situ keratomileusis (LASIK)?
More than 50% of flap folds occur within the first day, and over 90% occur within the first week post-operatively. Not all folds need to be repaired, but visually significant folds should be repaired within 24 hours.
Which best describes the course of the ophthalmic artery in the orbit in relation to the optic nerve:
The ophthalmic artery enters the orbit infero-lateral to the optic nerve, with which it is in close association. In the posterior third of the orbit the ophthalmic artery travels superiorly and medially across the optic nerve to travel superior and medially to the optic nerve. The correct answer is therefore that the ophthalmic artery runs, relative to the optic nerve, from inferior to medial.
What structures do the vortex veins drain?
The vortex veins drain the choroid, ciliary body and the iris (not the retina).
What nerves are derived from nasociliary nerve
The anterior and posterior ethmoidal nerves are derived from the nasociliary nerve.
What is Sampaolesi line?
Sampaolesi’s line describes pigmentation anterior to Schwalbe’s line and occurs in pigment dispersion syndrome and pseudoexfoliation.
What is commotio retinae?
Commotio retinae describes diffuse retinal oedema following blunt trauma likely due to transient ischaemia and disruption of axoplasmic flow.
Where are Midget ganglion cells and midget bipolar cells mainly found?
Midget ganglion and midget bipolar cells synapse with cones in a 1:1:1 ration and occur most often in the fovea. This neural exclusivity helps to explain the high resolution of the foveal region.
Features of image formed by Indirect Ophthalmoscopy
vertically and horizontally inverted
real
located between the observer and the lens, at or near the second principle focus
located about 40-50 cm from the observer who must accommodate to view the image
Image size during Indirect ophthalmoscopy in Emmetropia
the image size is the same regardless of position of lens
Image size during Indirect ophthalmoscopy in Hypermetropia
image size decreases as lens moves away from eye and increases nearer eye (image outside 2nd principle focus)
Image size during Indirect ophthalmoscopy in Myopia
image size increases as lens moves away from eye and reduces nearer eye (image within 2nd principle focus)
In VEP, to measure visual acuity, what does the P100 denote?
The amplitude (not the latency) of the P100 can be used as an objective measure of the visual acuity.
Ischaemia due to occlusion of a calcarine artery would be expected to produce what visual field defect?
Ischaemia to a calcarine artery produces a congruous defect (more posterior the defect, more congruous) and there is often macular sparing because of anastomoses between the middle and posterior cerebral arteries at the very pole, where the macular fibres terminate.
Metastatic vs Dystrophic calcification
Metastatic: occurring in hypercalcaemic states e.g. deposition of calculi in renal tubules
Dystrophic: occurring in dead or damaged tissues in the presence of normal serum calcium concentration, e.g. atheroma, phthisical bulbi, tuberculoma of lung
Facts about the anatomy of the LPS
it turns into aponeurosis where the superior transverse ligament of Whitnall is found
it is attached to the lesser wing of the sphenoid bone
it originates at a point superolateral to the optic foramen
Where do flame haemorrhages occur?
RNFL
Where do dot and blot haemorrhages occur?
Dot and blot haemorrhages occur in both the inner plexiform and outer plexiform layers. Hard exudates and CMO occur in the outer plexiform layer.
Pupillary sympathetic pathway (1st, 2nd and 3rd order neurons)
First order: hypothalamus along the brainstem to synapse in the ciliospinal center of Budge
Second order: centre of Budge to superior cervical ganglion
Third order: superior cervical ganglion, travels along the carotid plexus, branches join the ophthalmic division of the trigeminal nerve and pass through the ciliary ganglion to the nasociliary and short ciliary nerves
How many layers are present in the primary visual cortex
6
What does layer 4 of the Primary visual cortex do?
receives fibres from the macula
What does layers 2 and 3 of the Primary visual cortex do?
project to the secondary visual cortex
What does layer 5 of the Primary visual cortex do?
projects to the superior colliculus
What does layer 6 of the Primary visual cortex do?
projects to the LGN
What percentage of axons does the maculopapillary bundle contribute to?
the maculopapillary bundle constitutes 90% of all axons leaving the eye
What does digoxin do to vision?
Digoxin causes xanthopsia (yellow-blue discoloration of vision) and rarely photopsia and pain on eye movements.
What is the most common motifs in the amino acid sequence of collagen?
glycine-proline-X and glycine-X-hydroxyproline, where X is any amino acid other than glycine, proline or hydroxyproline
What happens in Type 2 hypersensitivity?
the antibodies produced by the immune response bind to antigens on the patient’s own cell surfaces. IgG and IgM antibodies bind to these antigens to form complexes that activate the classical pathway of complement for eliminating cells presenting with foreign antigen. The reaction takes hours to a day. Hemolytic anemia is an example.
What happens in Type 3 Hypersensitivity?
soluble immune complexes form in the blood and are deposited in various tissues where they may trigger an immune response according to the classical pathway of complement activation. The reaction takes hours to days to develop. Serum sickness and Arthus reaction are classical examples.
Where does myelination of the ganglion nerve fibres commence?
Ganglion nerve fibres become myelinated by oligodendrocytes immediately on exiting the lamina cribrosa.
Which Y shaped suture is upright and which is inverted in the lens?
The anterior Y-shaped suture of the lens is upright and the posterior oneis inverted.
Boundaries of the nasolacrimal duct
The nasolacrimal canal is formed by the maxilla, the lacrimal bone and the inferior nasal concha.
What connects the lateral to third ventricles
Foramen of Munroe
What connects the third to the fourth ventricle
Cerebral aqueduct of Sylvius
What is the lymphatic drainage of the eyelids?
The eyelids have lymphatic drainage laterally to the preauricular and intraparotid lymph nodes and medially to the submandibular and submental lymph nodes. These all drain into the cervical chain. There are no lymphatics in the deep orbit.
Arteries that make up the circle of willis?
Anterior cerebral arteries
Anterior communicating artery
Internal carotid arteries
Posterior cerebral arteries
Posterior communicating arteries
What is Visioscopy?
Visioscopy is a test for eccentric fixation using a direct ophthalmoscope fitted with a reticule target. The patient is asked to fixate on the centre of the target. The location of the anatomical centre of the fovea is measured on the reticule scale and provides a measure of the degree of eccentric fixation.
Which interleukins suppress the inflammatory response?
IL-4, IL-10 and IL-13 act to suppress inflammatory cytokines and the immune response. Interleukins also function as growth and differentiation factors.
Where do the lateral corticospinal tracts decussate at?
The lateral corticospinal tracts mediate voluntary, skilled motor activity. Fibres originate in the motor cortex, descend through the medullary pyramids where over 90% of fibres decussate to form the lateral corticospinal tracts (the remainder form the ventral corticospinal tracts). The lateral corticospinal tracts then synapse with second order motor neurones in the ventral horn of the spinal column which directly innervate skeletal muscle
Which complement component is present in the highest serum concentrations?
C3
Zeiss IOLMaster optics
The Zeiss IOLMaster is a non-contact method that uses two coaxial laser beams that are partially coherent. The beams produce an interference pattern that is used to interpret measurements, thus the technology is referred to as partial coherence interferometry. It is highly reproducible and less operator-dependent than ultrasound biometry. The machine can measure keratometry, axial length, anterior chamber depth and corneal white-to-white diameter.
Biopsy of a lower lid lesion reveals a keratin-filled cavity within the dermis lined by keratinized stratified squamous epithelium.
What is the diagnosis?
The histology report in the question above describes dyskeratosis, which is keratinisation within the dermis, rather than hyperkeratosis which is increased thickness of the epidermis. The most likely diagnosis is an epidermoid cyst.
What is the Cloquet Canal a remnant of?
Hyaloid artery
Which nerve bundle does LHON most affect?
LHOA affects the papillomacular bundle most severely.
What kind of aberrations do aphakik spectacle lenses do?
Large convex lenses (e.g. aphakic glasses) produce:
pin-cushion effect
ring scotoma
jack-in-the-box phenomenon
spherical aberration
These effects are due primarily to the strong prismatic effect at the edge of these large prescriptions.
Where is pseudoexfoliation material produced?
Pseudoexfoliation material is produced by abnormal basement membranes of ageing epithelial cells in the trabeculum, lens capsule, iris and ciliary body. It is more common in females
What is the most abundant immunoglobulin in the serum
IgG
IgA
IgM
IgD
IgE
Stages of Trachoma
Stage I: involvement of the conjunctival stroma
Stage II: involvement of the cornea with pannus formation
Stage III: fibrous replacement of inflamed tissue
Stage IV: contraction with entropion and trichiasis.
Neovascularisation of the disc fills initially during which stage of the fluorescein angiogram?
NVD are supplied by the retinal circulation and fill with the early arterial phase of the angiogram.
Choroidal melanoma vs haemangioma on B scan USS?
A choroidal melanoma is a dense tumour with low blood flow and high absorption of ultrasound; these characteristics cause low reflectivity or acoustic hollowness. With brachy or radiotherapy reflectivity increases. A haemangioma by contrast has a very high blood flow and low absorption of ultrasound, which results in high reflectivity.
What is the blood supply to the thyroid gland?
The thyroid gland is supplied by the superior thyroid artery which is a branch of the external carotid artery and the inferior thyroid artery which arises from the thyrocervical trunk which is derived from the subclavian artery.
Which biochemical process produces the most net ATP molecules per molecule of glucose than enters the reaction
The citric acid cycle produces the most energy- the equivalent of 30 molecules of ATP for each glucose molecule that enters. Glycolysis produces 6 molecules of ATP for each glucose molecule. The pentose phosphate cycle produces pentose for DNA/RNA synthesis and NADPH for biosynthetic reactions, while gluconeogenesis is an anabolic (not catabolic) process involving the production of glucose from precursors.
Which of the following is essential for unique genetic fingerprinting
Genetic fingerprinting involves the detection of variable number tandem repeats (VNTR), which are highly polymorphic sequences of DNA, the pattern of which on blotting is unique for each individual
Best test for assessing Chloroquine retinopathy
Colour vision testing and threshold central visual field testing are important in evaluating sub-clinical retinopathy
What percentage of optic nerve fibres when decussating at the chiasm go to the LGN
90%
What percentage of optic nerve fibres when decussating at the chiasm go elsewhere
10%
These fibres target:
the superior colliculus: involved in visual grasp reflex, automatic scanning of images
the pretectal nucleus: involved in pupillary light reflex
the parvocellular reticular formation: arousal function
the retinohypothalamic tract : photoperiod regulation
What do the variable regions of the immunoglobulin molecule correspond to?
The variable regions of the immunoglobulin molecule are the amino termini of both the light and heavy chains.
Features of the Hess Chart
In a Hess chart, each square is 5 degrees. The central field is 15 degrees from primary position while the peripheral field is 30 degrees from primary position. The patient is seated at 50cm from the screen. To test the left eye, the red lens is placed in front of the right eye, and green lens in front the left eye. The red targets are seen only by the right eye (fixing eye). The patient is asked to superimpose the green light onto the red light and these positions are marked.
What is the blood supply of the eyelids
The eyelids are supplied by the palpebral arcades (marginal and peripheral arcades) which are themselves supplied from both medial and palpebral ends by feeder arteries as follows:
medial palpebral artery: supplied by the angular artery (branch of facial artery, branch of external carotid) and the dorsalis nasi (branch of ophthalmic artery, branch of internal carotid)
the lateral palpebral artery: supplied by the transverse facial artery (branch of external carotid) and the lacrimal artery (branch of ophthalmic artery, branch of internal carotid)
How thick is the tear film?
more recent studies using high resolution OCT and other techniques suggest the thickness is between 3 to 5 micrometers.
Where is the anterior ethmoid foramen found?
The anterior ethmoid foramen occurs at the junction of the frontal and ethmoid bones in the medial orbital wall. It transmits the anterior ethmoidal vessels and the anterior ethmoidal nerve.
Which secondary glaucoma is caused by elevated episcleral venous pressure?
carotid-cavernous fistula
Sturge-Weber syndrome
obstruction of the superior vena cava.
A 28-year-old man presents to casualty with left eye visual disturbance following a punch to the eye. Indirect ophthalmolscopy reveals 90 degrees of disinsertion of the retina from the pars plana.
Retinal dialysis represents a disinsertion of the retina from the ora seratta. It can occur spontaneously (usually inferotemporal). Superonasal dialysis is almost pathognomonic for trauma.
What is the Pulfrich phenomenon?
The Pulfrich phenomenon reflects delayed conduction in the demyelinated optic nerve (in optic neuritis) and occurs where oscillating objects viewed binocularly and moving in one plane (e.g. a pendulum) appear to have three-dimensional movement.
What are rods responsible for?
contrast
brightness
motion
What are cones responsible for?
fine resolution
spatial resolution
colour vision
Where does the trochlear nerve decussate?
The trochlear nerve is unusual in that it decussates before leaving the brainstem. It is also unusual in that it is the only somatic efferent nerve to emerge from the posterior aspect of the central nervous system.
What immune cells does the tear film contain?
IgA
IgG
IgM
lactoferrin
lysozyme
betalysin
Where is the uveal tissue is most strongly attached to the sclera at?
Optic disc
Which part of the retina is the last to be perfused in a premature infant?
Temporal retina
The temporal retina is usually the last to be perfused in a premature infant, and it is from this area of ischemic retina that growth factors are produced that drive new abnormal vessel formation. If left untreated vasoproliferation can lead to retinal detachment and blindness.
What is the nonconventional drainage pathway of aqueous humour?
The non-conventional pathway refers to drainage of aqueous via the intercellular spaces between ciliary muscle fibres and the loose connective tissue of the suprachoroidal space.
Where does the inferior oblique muscle originate?
The inferior oblique is the only extrocular muscle to originate outside the orbital apex. It originates behind the orbital margin lateral to the nasolacrimal duct and passes beneath the inferior rectus to insert on the sclera between the inferior rectus and the lateral rectus; with the posterior margin of the insertion corresponding to a point 2mm below and 2mm lateral to the macula.
Lens capsule thickness anteriorly and posteriorly
The lens capsule varies in thickness being thinnest at the poles, measuring about 2 micrometers at the posterior and 15 micrometers at the anterior pole.
Where is CSF made?
by the modified ependymal cells of the choroid plexus
How does the ventricular system communicate with the subarachnoid space?
The ventricular system communicates with the subarachnoid space via the roof of the fourth ventricle.
What is the largest extraocular muscle?
Medial rectus
What is true of diurnal intra-ocular pressure fluctuation
IOP is typically highest in the morning, with 80% of patients peaking between 8am and 12pm
Over-treatment of HSV keratitis with topical antivirals can lead to
follicular conjunctivitis
punctate keratitis with photophobia
sterile corneal ulceration
Histo-pathologically the limbus may be BEST described as extending from:
Pathologists define the limbus as a block of tissue bordered:
anteriorly by a vertical line passing through Schwalbe’s line (termination of Descemet’s membrane) and the junction of the conjunctival and corneal epithelium and
posteriorly by a line from the scleral spur perpendicular to the tangent of the external surface.
What are the landmarks of the surgical limbus
The surgical limbus is the blue-grey transition zone visible between the clear cornea and the opaque sclera once the conjunctiva and Tenon’s have been removed. Incisions made here will pass anterior to the trabecular meshwork and Schlemm’s canal.
How thick is the choroid:
The choroid is 100-200 micrometers thick, being thickest at the posterior pole and thinner anteriorly.
Which ECM is integral to the structure of cellular basement membranes?
Laminin
The most common colour vision defect is caused by
Deuteranomaly is caused by defective M-cones and is by far the most common form of color blindness, weakening the ability to differentiate red and green hues in as much as 5% of all males.
How tall are the RPE cells
The RPE cells measure 14 micrometers tall in the centre of the retina and 10 micrometers in the periphery
Subtypes of Rhabdomyosarcoma
Rhabdomyosarcoma sub-types:
embryonal: most common type
botryoid
spindle cell
alveolar: worst prognosis
pleomorphic: best prognosis
In which layers do crossed vs uncrossed fibres terminate in the LGN?
Crossed fibres from the nasal retinae terminate on layers 1, 4 and 6. Un-crossed fibres (those from the ipsilateral eye) terminate on layers 2, 3 and 5
Chemotherapy drugs and mechanism of action
Methotrexate is a folate antagonist.
Azathioprine is a purine analogue.
Cyclophosphamide is an alkylating agent.
Cyclosporin is a T-cell inhibitor which suppresses IL-2.
Mitomycin C is a DNA crosslinker.
What is the correct order of structures encountered from superficial to deep through an eyelid incision in the upper eyelid crease:
skin, orbicularis, septum, orbital fat, levator aponeurosis, Muller’s, conjunctiva
Which portion of the iridocorneal angle is usually the easiest for distinguishing landmarks on gonioscopy?
The inferior angle (viewed through the superior mirror on a Zeiss gonioprism lens) is usually the widest and is generally considered the easiest portion for distinguishing landmarks.
The first reading of a toric lens in a focimeter is +1.00D at 90 degrees and the second reading is +3.00D at 180 degrees. The sphero-cylinder equation for the lens is:
To determine the sphero-cylinder formula from focimeter readings:
- Take the more positive reading, this is the spherical power
- Take the difference of the 2 power values (more pos - more neg), this is the size of the negative cylinder
- Take the axis of the more negative reading, this is the axis of the negative cylinder.
Thus the equation in this case is: +3.00DS/-2.00 x 90
By transposition, this equates to the same as: +1.00DS/+2.00DS x 180
Note: determining the sphero-cylinder formula from a power cross is different to determining the sphero-cylinder formula from a focimeter reading.
Which HIV drugs are reverse transcriptase inhibitors
Zalcitabine, zidovudine and didanosine are all reverse transcriptase inhibitors
Which HIV drugs are protease inhibitors
Ritonavir is a protease inhibitor.
Which retinal layer accounts for the petalloid appearance of cystoid macular oedema as seen in fluorescein angiography?
The radiating fibres of Henle in the outer plexiform layer lead to the cystic spaces in CMO.
The maximal number of axons in the optic nerve is achieved at which point in life:
The maximal number of axons in the optic nerve is achieved at 14-15 weeks gestation when they number nearly 6 million. The number declines steadily thereafter so that at birth there are approximately 1.3million
When is the Bonferroni correction used
The Bonferroni correction is used to reduce the chance of a Type I error occurring (that is the null hypothesis being falsely rejected).
Zonular fibres are produced by the:
Zonules are synthesised and maintained by cells of the non-pigmented ciliary epithelium.
