basic sciences part 2 Flashcards
what is keratometry
Measures the anterior corneal surface curvature.
what is corneal topography
Measures and quantifies the curvature of the whole cornea and provides information on its shape. It uses placido-disc systems which project concentric rings of light on the anterior corneal surface.
indications for the use of corneal topography
keratoconus, astigmatism, laser eye surgery and contact lens fitting.
what is US pachymetry
Can be used to measure the central corneal thickness (CCT) using an ultrasonic probe. Normal CCT is between 530 and 545 μm.
what is OCT
near-infrared waves through the pupil to the retina to produce a cross-sectional and three- dimensional image of the retina
indication for OCT
monitor the progression of macular and optic diseases.
what is fluorescence angiography
In fluorescence angiography (FA), sodium fluorescence, a dye, absorbs blue light (wavelength 465–490 nm) and emits a yellow-green light (530 nm). It is injected into a peripheral vein to circulate to the eye. It passes through the short posterior ciliary artery into the choriocapillaris about 8–12 seconds post- injection and then enters the retinal circulation a second later
SEs of fluorescence angiography
urine discolouration, nausea, vasovagal syncope, anaphylaxis (rare) and it is contraindicated in shellfish allergy.
what is the indocyanine green angiography
visualize the choroid vasculature better
in who is indocyanine green angiography contradicted
pregnancy
seafood and iodine allergies
what is fundus autofluorescence
detects lipofuscin already present within the retinal pigmented epithelium (RPE)
fundus autofluorescence used where
Best disease and for monitoring geographic atrophy.
what is electroretiogram (ERG)
electrical activity of the retina in response to a light stimulus.
what is the electrocular oculogram (EOG)
reflects the activity of photoreceptors and RPE; thus retinal diseases proximal to the photoreceptors give normal EOG readings.
ERG and EOG can be used where
Best disease
retinitis pigmentosa.
what is tonometry
measure IOP
Follws the imbert hick law
factors that can cause incorrect measurements for tonometry
● Excessive fluorescein: Overestimates IOP
● Low or high CCT: Underestimates or overestimates IOP, respectively
● Astigmatism
● Calibration errors
what is gonioscopy
determine whether the iridocorneal angle is open or closed.
structures seen thru gonioscopy ant - post
● Schwalbe line
● Nonpigmented trabecular meshwork
● Pigmented trabecular meshwork: Pigmentation is not present at birth and
increases with age, mainly following puberty
● Scleral spur: An anterior protrusion of the sclera that marks the attachments
of the ciliary body’s longitudinal fibres
● Ciliary body
what is perimetry
detect visual field defects and is commonly used in glaucoma and neuro-ophthalmic conditions
examples of perimetry
Humphrey visual field analysis or Goldmann visual field testing.
field defects of glaucoma
● Nasal step
● Paracentral depressions: Most commonly superonasally
● Arcuate defects: Combination of paracentral depressions
● Ring scotoma: Superior + inferior arcuate defects
● Tunnel vision with a temporal sparing of visual field
indications for CT
orbital fractures, orbital cellulitis, thyroid eye disease and cerebral haemorrhages.
indications for CT angiography
investigate for subarachnoid haemorrhage and intracranial aneurysms, for example, in cases of third nerve palsy.
what are the three fundamental properties of lasers
coherency (all emitted photons are in the same phase)
monochromaticity (single wavelength)
collimation (narrow with minimal divergence).
lasers are constructed using which three parts
● A source of energy: Light or electrical.
● A medium: Containing atoms or molecules that undergo stimulated emission
and is the major determinant of the wavelength. They can be in the form of:
Gas (e.g. argon, krypton, carbon dioxide)
Liquid (e.g. dyes)
Solid (e.g. neodymium-doped yttrium aluminium garnet [Nd:YAG] crystals)
● An optical resonator that uses mirrors to amplify light.
UV light can damage which structures
photochemical injuries to the lens and cornea,
infrared can damage what
thermal burns to the lens and cornea
near infrared damages what
thermal burns to the lens and retina
visible light can damage what
retinal burns
how are lasers classified
according to their hazardous effects on the human body. Class 1 is harmless to the eye, while class 4 causes the most harm.
which light does melanin absorb and where is it found
Found mainly in the RPE and choroid. It absorbs most of the visible spectrum and infrared wavelengths.
which light does xanthophyll absorb
Present at the macula. Absorbs blue light (450–495 nm).
which light does Hb absorb
Absorbs blue, green (495–570 nm) and yellow light
570–590 nm
what is photovaporisation
Vaporization of water from tissues occurs in types of lasers such as carbon dioxide lasers, as they raise the temperature beyond 100°C.
what is photocoagulation
Absorption of laser emissions by tissues causes a rise in temperature, leading to protein denaturation. Panretinal photocoagulation (PRP) used in diabetic retinopathy is a good example.
types of photocoagulative lasers
● Argon blue-green: Absorbed by melanin, haemoglobin and xanthophyll. Thus it is not used on the macula.
● 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.
what is photochemical
These work by breaking chemical bonds that hold tissue together using ultraviolet light, in a process called photoablation
types of 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.
what is photo ionising
estruction 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.
criteria for severely sight impaired
● Visual acuity (VA) <3/60 Snellen.
● VA 3/60–6/60 with reduction in visual field (VF).
● VA >6/60 with significantly reduced VF (e.g. inferior altitudinal defects or
bitemporal hemianopia).
criteria for sight impaired
● VA 3/60–6/60, with full VF.
● VA 6/60–6/24 with moderate reduction of VF.
● VA ≥6/18 with significant reduction of VF (e.g. homonymous hemianopia).
DVLA criteria for car and motorcycle drivers
- Ability to read a car registration plate (post-September 2001) at a distance of 20 metres, using corrective glasses or contact lenses if needed.
- VA ≥ 6/12 with both eyes open, or one eye if monocular.
- VF of at least 120° on the horizontal with extension of at least 50° to the right
and left. No significant defect encroaching 20° of fixation above or below the horizontal meridian should be present.
specific cases that must be notified to the DVLA
● Diplopia: Patients may resume driving after confirmation that diplopia is controlled.
● VF defects: Such as retinitis pigmentosa, bilateral glaucoma or bi-temporal hemianopia.
● Nyctalopia.
● Blepharospasm: Even if treated, patients with severe blepharospasm are
usually not licenced to drive. Mild cases may be licenced.
which sutures would you use for each Eyelids and sclera Conjunctiva, muscles and cornea Cornea, sclera and limbus Iris Limbus
Silk
Polyglactin 910
Nylon
Polypropylene Polyglycolic acid
what is vision 2020 and their aims
Vision 2020 was established by the International Agency of the Prevention of Blindness (5) and supported by the World Health Organization (WHO) (6) to eliminate preventable causes of blindness by the year 2020. The following conditions are in their current objectives:
● Cataract: The most common cause of blindness in the world.
● Trachoma: The most common cause of infectious blindness.
● Onchocerciasis: The second most common cause of infectious blindness.
● Refractive errors: The most common cause of visual impairment.
● Childhood blindness: Vitamin A deficiency (the most common cause of
nutritional blindness in Africa), measles, retinopathy of prematurity (ROP) and cataract.
