exam Flashcards
convert cross spectacle to power cross diagram
+1.50/-2.50 by 130 degrees
To convert the prescription +1.50 / -2.50 × 130° to a power cross, we need to calculate the power at the two principal meridians that are 90° apart.
Step 1: Understanding the Prescription
The prescription consists of:
Spherical power (S): +1.50 D
Cylindrical power (C): -2.50 D
Axis: 130°
Step 2: Identify the Principal Meridians
Since the cylindrical axis is at 130°, the two principal meridians are:
130° (Axis meridian): This meridian has the spherical power only.
130° + 90° = 40° (Meridian perpendicular to the axis): This meridian has the spherical power + cylindrical power.
Step 3: Calculate the Power at Each Principal Meridian
Power at 130° (Axis meridian):
This meridian has the spherical power, i.e., +1.50 D.
Power at 40° (Perpendicular meridian):
This meridian has the spherical power plus the cylindrical power.
Powerat40°
=
+
1.50
+
(
−
2.50
)
Powerat40°=+1.50+(−2.50)
Powerat40°
=
+
1.50
−
2.50
=
−
1.00
D
Powerat40°=+1.50−2.50=−1.00D
Step 4: Represent as a Power Cross
The power cross will show the powers at these two meridians:
mathematica
Copy code
-1.00 D @ 40°
—————–
+1.50 D @ 130°
This power cross indicates that:
The power at 40° is -1.00 D.
The power at 130° is +1.50 D.
This representation helps visualize the distribution of refractive power across the two main meridians.
convert cross diagram to +2 at 90 degrees, -1 at 180
answer +2/-3 at 90
what is the embryological derivate of the lens
Surface Ectoderm
How to quantify repeatability ?
Quantifying Repeatability:
Standard Deviation (SD): Measures the dispersion of repeated measurements around the mean.
Coefficient of Variation (CV): The ratio of the standard deviation to the mean, often expressed as a percentage. A lower CV indicates higher repeatability.
Intraclass Correlation Coefficient (ICC): Evaluates the consistency of repeated measurements. The closer the ICC is to 1, the better the repeatability
Factors Affecting Repeatability:
Factors Affecting Repeatability:
Observer variability: Differences between measurements taken by the same observer.
Instrument variability: Fluctuations due to the instrument itself.
Environmental factors: Changes in lighting, room temperature, or patient positioning.
What stains prions?
Toluidine blue-O
What is the mechanism of action of benzomechonium?
It is a surfactant
The average width of the corneal endothelium?
Thickness 4-6um
Features of the corneal endothelium (6)
- Thickness 4-6um
- It is a monolayer of interdigitating hexagonal cells joined by tight junctions
- At birth: 1 million cells with approximately 3800 endothelial cells/mm2; these cells are loss with ageing. Cornea endothelium do not regenerate but rather stretch to fill gaps left by cell loss
- Schwalbe’s line is the termination of the Descemet’s membrane and delineates the outer limit of the cornea endothelium -it is a structure that can be seen usually only on gonioscopy
- Posterior embryotoxon is the thickening and anterior displacement of the Schwalbe’s line
- Function of the cornea endothelium is to keep cornea dehydrated and clear. If cell count < 500cells/mm2, pump action will be insufficient and this could lead to corneal oedema
What stage is the poly A tail cleaved?
It is post transcription, pre translation
Function of nucleodiase?
A nucleotidase is a hydrolytic enzyme that catalyzes the hydrolysis of a nucleotide into a nucleoside and a phosphate. EC no. CAS no. For example, it converts adenosine monophosphate to adenosine, and guanosine monophosphate to guanosine.
MRI scanning contraindications
Absolute: Cardiac Pacemaker.
Implanted cardiac defibrillator.
Internal pacing wires.
Clips such as cerebral, carotid, or aortic aneurysm.
Cochlear implants.
Any implant held in by magnet.
Swan-Ganz catheter.
Pregnant/possibly pregnant
Antibodies prominent in lupus?
Anti-dsDNA (antibodies to DNA). - most promninent
Antinuclear antibody (ANA)
Anti-RNP.
Anti-Smith (Sm).
Anti-SS-A (also called Ro).
Anti-SS-B (also called La).
what is the refractive index of hard contact lens ?
-3 D
Xeroderma pigmentosa defect
Defect in DNA repair. Characterized by severe UV exposure
Galilean telescope eye piece ?
Objective lens: convex (plus) lens, closest to the object
Ocular lens: minus lens (concave), closest to the eye
Foramen for maxillary nerve
Foramen rotundum
what is the gene upregulated in uveal melanoma?
Braf
Tx of melanoma; BRAF inhibitos; vemurafenib
Genetic diagram of AD/ AR
draw
Decentering lens - moving prism ?
Prism
no optic centre
displaces one line of cross with respect to cross
direction of displacement constant
IOL in AC- how much less power ?
2D
Mechanism of mitomycin C?
Mitomycin C inhibits DNA synthesis and cross-links DNA at the N6 position of adenine and at the O6 and N2 positions of guanine
embryology of the cornea
The mature cornea is composed of three layers (epithelium, stroma, and endothelium). Each layer has distinct embryologic origins. The corneal epithelium is a derivative of surface ectoderm proximal to the developing lens (Figure 3). The corneal stroma and endothelium, along with a litany of other structures of the anterior segment, are derived from successive waves of invading neural crest cells. [7] The mature, transparent cornea is ultimately formed when the mesenchymal-derived stromal keratocytes produce a highly organized stromal collagen matrix.
Gap junctions?
Gap junction has a 2nm gap between cells
Occur in cardiac muscle and ocular muscles
Allow passage of larger ions such as Ca2+ and signalling molecules to permit coordinated responses
Pseudomonas
1) Pseudomonas aeruginosa
aerobic
motile
water soluble
green pigment ( pyocin).
2) Penetrates corneal epithelium via protease and causes keratitis. It is the most common cause of bacterial keratitis worldwide
Produces an exotoxin as part of type 3 secretion system ( T3SS)
More severe cornea disease occurs with inhibition of TLR4/5 (toll like receptors and high concentration of flagellin)
3) It is a gram-ve bacteria.
Fungi cell wall
Mannoproteins, chitin, glucan, membrane proteins, cell membrane
Oxygenation/haemoglobin curve and co2
The effect of carbon dioxide (CO₂) on the oxyhemoglobin dissociation curve is described by the Bohr effect. Increased levels of CO₂ result in a rightward shift of the curve, meaning that hemoglobin releases oxygen more readily to the tissues. This shift is due to the formation of carbonic acid, which decreases blood pH. Conversely, lower CO₂ levels shift the curve to the left, enhancing hemoglobin’s affinity for oxygen.
For a more detailed understanding, refer to additional resources on the Bohr effect and hemoglobin.
Lymph node follicle role
maturation of b cells
passive immunity versus innate immunity
Active immunity occurs when our own immune system is responsible for protecting us from a pathogen. Passive immunity occurs when we are protected from a pathogen by immunity gained from someone else.
sarcoid granuloma
non cesating granuloma
Physis buli
CALCIFCATION OF EYE - non metastatic
Phthisis bulbi is an clinical condition representing an end-stage ocular response to severe eye injury or disease damage, related to a variety of causes leading to scarring, inflammation, atrophy and eventually disorganization of the globe and intraocular contents.[1] Also called end-stage eye, phthisis bulbi can be described as a shrunken, collapsed, non-functional eye and presents with a small squared off shape, opaque and thickened cornea, thickened sclera, iris neovascularization, cataract, cyclitic membranes, and ciliochoroidal or retinal detachment.[2] A mnemonic rule used to describe phthisis bulbi is ‘‘7S” referring to an eye that is: Soft - Shrunken - Shapeless - Sightless - Structureless - Squared - Sore.
Effect of bromodine on the eyelid
cause eyelid retraction by increasing Muller muscle tone
Hydroxychloroquine mechanism of toxicity
Hydroxychloroquine retinopathy causes destruction of macular rods and cones with sparing of foveal cones. This pattern provides the typical bullseye appearance. RPE migrates into the areas of destructed photoreceptors, causing pigment laden cells to be detected in the outer nuclear and outer plexiform layers[2]. Hydroxychloroquine keratopathy is caused by deposition of unmodified hydroxychloroquine salts within the epithelium
In a normal fundus without retinal pathology:
In a normal fundus without retinal pathology:
Blood vessels appear dark
Blood absorbs blue (~488nm) or green (~514nm) light used in FAF imaging
Optic nerve usually appears dark
Absence of RPE or lipofuscin in this region, depending on the device
Fovea typically visualized as a spot of hypo-autofluorescence
High concentration of light-absorbing xanthophyll pigment in this area with blue or green short-wavelength FAF
Esotropia with prism fixed?
Base out opposite to the movement of the eye
Human papilloma virus
DNA
chromatic aberration
dispersion of white light and shortest wavelength travels furthest
Northern blot used for detection of ?
Northern blot is a laboratory technique used to detect a specific RNA sequence in a blood or tissue sample.
electrodiagnostic test
is a diagnostic test that measures the electrical activity of the retina in response to a light stimulus.
Random error effect in trials can be overcome by:
It can be minimized by increasing sample size, studying a more homogeneous population, or using more precise measurement tools
bacteria that can penetrate the cornea?
Corynebacterium diphtheriae, Haemophilus influenzae, Neisseria gonorrhoea, Neisseria meningitidis, and Listeria, Psudomonas species
Birdshot HLA
HLA A29
Effect of pilocarpine?
increases smooth muscle tone, contracts the pupillary and iris sphincter muscles, and induces miosis.
Duochrome test -
One way to remember this is “RAM GAP,” which stands for “red add minus” and “green add plus.” The duochrome test is a half-red, half-green chart designed to assist with a patient’s final sphere adjustment
What layer is the trabecular meshwork derived from ?
Neural crest
Possible MRI contraindication
Possible: Tattooed makeup (eyeliner, lips, etc.) Any type of prosthesis (eye, penile, etc.)
Autoantibodies in type 2 diabetes?
Islet Cell Cytoplasmic Autoantibodies (ICA)
Glutamic Acid Decarboxylase Autoantibodies (GADA)
Insulinoma-Associated-2 Autoantibodies (IA-2A)
Insulin Autoantibodies (IAA)
Zinc Transporter-8 Autoantibodies (ZnT8A)
effect of insulin on protein
does not stimulate proteinlysis
p value depends on two factors?
Magnitude and sample size
Coherent?
Colliminating?
Coherent - same wavelength in a phase
Colliminating? waves are parallel - “cool-imminating
Neisseria Gonorrhea grows on what type of agar plate?
Choclate agar
least cycloplegic medication
Cycloplegic activity from most to least:
Atropine, hyoscine, cyclopentolate, tropicamide, homatropine
Post op diplopia test ?
Botox, maddox rod, add in more
B scan best mega hertz ?
10mhz
axial length forms
1) Axial length < 22mm : Haigis, Hoffer Q
2) Axial length between 22 -26 mm :SRK/T or Barret Universal II
3) Axial length> 26mm : Haigis, SRK/T
4) If previous refractive surgery-Haigis L
Strep A thermophile or mesophile
thermophile
allele sequences ?
Perspex plate
Slight light
what percentage of patients with Protein c resistance have CRVO?
12%
Two hit hypothesis ?
Tumor suppressor genes often require both alleles to be inactivated or lost to contribute to cancer development. This concept is known as the “two-hit hypothesis” (proposed by Alfred Knudson), where:
The first hit is a mutation in one allele of the tumor suppressor gene.
The second hit could be a mutation, deletion, or epigenetic silencing of the second allele, leading to complete loss of function
Example of tumour suppressors
p53, RB1, Brac1 and BRAC2, PTEN
What is the role of tumor suppressor gene is primarily responsible for controlling cell cycle progression?
Preventing the transition from G1 phase to S phase?
Which of the following statements about tumor suppressor genes is TRUE?
A) They promote cell growth and division.
B) Mutations in these genes typically lead to a gain-of-function effect.
C) Inactivation of both alleles is often required for tumor development.
D) They are less commonly associated with cancer compared to oncogenes.
C
Mutations in which tumor suppressor gene are frequently found in Li-Fraumeni syndrome?
A) BRCA2
B) NF1
C) TP53
D) VHL
TP53
Which of the following tumor suppressor genes is associated with the hereditary cancer syndrome called von Hippel-Lindau disease?
A) RB1
B) NF2
C) VHL
D) PTEN
VHL
PTEN is a tumor suppressor gene involved in which of the following cellular processes?
A) Regulation of the p53 pathway
B) Control of cell growth and apoptosis via the PI3K/AKT pathway
C) Maintenance of DNA repair mechanisms
D) Regulation of cell-to-cell adhesion
Answer: B) Control of cell growth and apoptosis via the PI3K/AKT pathway
Which tumor suppressor gene, when mutated, is most commonly associated with hereditary colorectal cancer, such as familial adenomatous polyposis (FAP)?
A) PTEN
B) RB1
C) APC
D) TP53
APC
Nystagmus - brief description?
By definition, nystagmus starts by a slow movement of the eye away from the visual target. The second movement brings the eye back to the visual target. If the second movement is slow, the nystagmus is said to be pendular. If this second movement is quick, the nystagmus is called jerk nystagmus. By convention, the direction of jerk nystagmus (eg., right-beating nystagmus) is named after the fast phase of nystagmus. In a right-beating nystagmus, the fast phase is to the patient’s right.
Nystagmus is an involuntary rapid and repetitive oscillation of the eye which can be physiological or pathological. There is a risk of amblyopia in young patients with nystagmus, so it is important to correct refractive error and treat the underlying cause.
● End-point nystagmus: Nystagmus at extreme gaze.
● Optokinetic nystagmus: Nystagmus due to fast-moving repetitive objects
Congenital Nystagmus
The nystagmus is horizontal, pendular or jerky and disappears during sleep.
It often has a null point – a position of gaze where nystagmus is minimal.
Common causes include sensory deprivation (e.g. bilateral cataracts), optic nerve hypoplasia or foveal hypoplasia (e.g. albinism).
Latent nystagmus
Horizontal and jerky nystagmus, but only becomes present on monocular occlusion (direction is away from the covered eye).
Most commonly associated with infantile esotropia.
Convergence retraction nystagmus
Co-contraction of horizontal muscles on attempted upgaze causing the globe to retract.
The medial rectus is the most powerful EOM. This causes eye convergence.
Caused by dorsal midbrain lesions (e.g. Parinaud syndrome).
Upbeat nystagmus
Downward drifting of the eye followed by a fast upward corrective saccade or beat. Caused mainly due to medulla lesions.
Peripheral vestibular nystagmus
A conjugate horizontal and jerky nystagmus that occurs due to a vestibular lesion (e.g. labyrinthitis). There is a slow drifting of the eyes towards the side of the lesion followed by a fast corrective saccade in the other direction.
Downbeat nystagmus
Upward drifting of the eye followed by a fast downward corrective saccade or beat. Caused mainly due to lesions at the craniocervical junction such as Arnold-Chiari malformations.
- Which type of nystagmus is typically associated with multiple sclerosis?
A) Downbeat nystagmus
B) Upbeat nystagmus
C) Internuclear ophthalmoplegia (INO)-associated nystagmus
D) Seesaw nystagmus
Answer: C) Internuclear ophthalmoplegia (INO)-associated nystagmus
A patient has nystagmus that increases in intensity when looking towards the fast phase direction. Which type of nystagmus is this?
A) Congenital nystagmus
B) Gaze-evoked nystagmus
C) Latent nystagmus
D) Vestibular nystagmus
gaze evoked
Which type of nystagmus is characterized by a slow drift of the eyes in one direction followed by a rapid corrective movement in the opposite direction?
A) Pendular nystagmus
B) Jerk nystagmus
C) Seesaw nystagmus
D) Gaze-evoked nystagmus
Jerk nystagmus
Which of the following best describes the direction of nystagmus?
A) The direction of the slow phase
B) The direction of the fast phase
C) The direction opposite to head movement
D) The direction of the pupil
The direction of the fast phase
Which of the following is the primary component of the fungal cell wall?
A) Cellulose
B) Chitin
C) Peptidoglycan
D) Glycogen
Chitin
In addition to chitin, which of the following polysaccharides is commonly found in the fungal cell wall?
A) Starch
B) Mannan
C) Cellulose
D) Pectin
mannan
The structural integrity of the fungal cell wall is primarily due to which component?
A) Glucans
B) Proteins
C) Lipids
D) DNA
Glucans
Trochlear nerve palsy is most commonly associated with which of the following conditions?
A) Intracranial aneurysm
B) Hypertension
C) Diabetes mellitus
D) Head trauma
Head trauma
Galilean versus the Keplerian telescope
Galilean Telescope
The Galilean telescope is a simple system consisting of 2 lenses:
Objective lens: convex (plus) lens, closest to the object
Ocular lens: minus lens, closest to the eye
The distance between the 2 lenses is determined by the difference in their focal lengths. The image produced is real and erect. It’s lighter, shorter, and cheaper than the Keplerian type, thus the first-choice prescription for children. It is also the first choice in cases of peripheral field loss; in these cases, the lens order is designed in reverse (plus lens closer to the eye), providing a wider visual field.
Keplerian Telescope
Also known as astronomical or prismatic, the Keplerian telescope is an optical system that uses 2 convex (plus) lenses, the objective lens being of smaller diopter power than the ocular. The distance between the lenses is the sum of their focal lengths. The image is real and inverted, requiring a prism to reverse the image, making it longer and heavier. It produces greater visual field and better optical quality than Galilean type and costs more.
tb versus sarcoid granuloma
TB is an infectious disease caused by M. tuberculosis morphologically defined by granulomas with caseous necrosis. Sarcoidosis is a systemic disease of unknown etiology, and is characterized by noncaseous granulomas.
orbit and eye volume
1) Anterior chamber
Average depth 3.11mm
Volume 220 ul
2) Posterior chamber
Average depth 0.52mm
Volume 60 ul
3) Vitreous cavity
Average depth 16.5mm
Volume 5.5 ml
ON length speciidc
Ocular 1
Orbital 20
Canaicular 5
Cranial 10
Cornea dimaeter and horizontal,
Where it is thickest and thinnest
Radius of curvature
Refractive power
Vertical diameter: 11.5mm
Horizontal diameter: 12.5mm
Cornea reaches adult size by 2 years of age
Different sources might cite the diameter of the cornea differently. Other potential values from Khng C et al include:
Vertical diameter: 10.63
Horizontal diameter: 11.46
2) Cornea thickness
Central thickness: 550um
Peripheral thicknesss: 1mm
Inferior temporal paracentral cornea is thinnest
Superior paracentral corneal thickest
3) Cornea radius, refraction and power
Radius of curvature: 7.8 mm anteriorly; 6.2-6.8mm posteriorly
Refractive index: 1.36
Anterior surface power: 49D
Posterior surface power: -6D
Totally power: 43D ( approximately ¾ of the total refractive power of the eye)
Fovea and blind spot
Key measurements:
17 degrees from the fovea
5-7 degrees in size
The fovea is 4mm away from the optic nerve head
The fovea is 0.8mm lower than the optic nerve head
reintal layer in location of axons of horizontal cell, amacrine cell and synapses of ganglion
Inner plexiform layer
Axons of bipolar and amacrine cells and synapses of ganglion cell
correlation between P value and sample size ?
The p-values is affected by the sample size. Larger the sample size, smaller is the p-values
sign levels of evidence?
Level 1: highest level meta analyses, systematic review
2: Meta anaylsys, systematic review, prospective cohort studies
3: Case control, retrospecitive
4: case series, uncontrolled cohort studies
5: Expert opinon, case reports
Laser causing photothermal effect
Two types: photovaporisation and photocoagulation
Examples of photocoagulatio
● Argon blue-green: Absorbed by melanin, haemoglobin and xanthophyll.
Thus it is not used on the macula.
1.8 Miscellaneous
● Krypton red (647 nm): Absorbed by melanin.
● Frequency-doubled Nd:YAG (532 nm): Absorbed by haemoglobin and melanin in the RPE and trabecular meshwork.
● Diode (810 nm): Emits near-infrared radiation and is absorbed by melanin.
Photoionzing
This type of laser causes destruction of tissues by altering the stable state between photons and electrons. An important example of photo-ionizing lasers includes Nd:YAG (1064 nm), which is used in posterior capsulotomy for treating posterior capsular opacification (PCO) and in peripheral iridotomy used in managing angle-closure glaucoma.
Photochemical laser
PHOTOCHEMICAL
These work by breaking chemical bonds that hold tissue together using ultraviolet light, in a process called photoablation. An excimer laser is a laser that causes photoablation and has important uses in refractive surgery:
● Photorefractive keratectomy (PRK): Corneal epithelium is first removed, then laser ablation is used to reshape the cornea.
● Laser-assisted in situ keratomileusis (LASIK): A corneal flap is created; the stroma is then ablated (to reshape the cornea) and the flap is replaced.
● Laser epithelial keratomileusis (LASEK): The corneal epithelium is peeled using 20% ethanol, laser ablation is performed and the epithelium is replaced.
mosaicism is what part of fertilisation
Germline fertilisation
pleiotropy, somatic mocasism, variable expression and non penterance
Pleiotropy refers to the phenomenon where one gene influences multiple, seemingly unrelated traits. FBN1
Somatic mosaicism: Somatic mosaicism refers to a condition where an individual has two or more genetically distinct cell populations within their body that arose from the same fertilized egg.
Variable Expression
Variable expression means that the same genetic mutation can produce different clinical features or severities of a disease in different individuals.
Non-penetrance
Non-penetrance occurs when a person inherits a genetic mutation that is associated with a disease but does not develop any symptoms of the disease.
MRI: rf pulse before or after magnetic field excite proton or electron
RF pulse is applied for a few milliseconds disturbs or flips the protons at the same time and out of alignment from the main magnetic field. The amount of this rotation or flip depends on the strength and duration of the RF pulse.
