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.
