Investigations Flashcards
What is keratometry and what is it used for?
Used to investigate the cornea
MEASURES ANTERIOR CORNEAL SURFACE CURVATURE
What is corneal topography used for?
MEASURES AND QUANTIFIES CURVATURE OF THE WHOLE CORNEA
USES PLACIDO-DISC SYSTEMS WHICH PROJECT CONCENTRIC RINGS OF LIGHT ON THE ANTERIOR CORNEAL SURFACE
INDICATIONS INCLUDE:
KERATOCONUS
ASTIGMATISM
LASER EYE SURGERY
CONTACT LENS FITTING
What is ultrasonic pachymetry?
CAN BE USED TO MEASURE THE CENTRAL CORNEAL THICKNESS (cct) USING ULTRAOSNIC PROBE
NORMAL CCT IS BETWEEN 530-545M um
What ocular coherence tomography?
USES NEAR INFRARED WAVES THROUGH THE PUPIL TO THE RETINA
PRODUCES CROSS SECTIONAL + 3d IMAGE OF THE RETINA
INDICATED IN ORDER TO DIAGNOSE AND MONITOR PROGRESSION OF MACULAR AND OPTIC DISEASES
What is fluorescence angiography?
SODIUM FLUORESENCE (DYE) ABSORBS A BLUE LIGHT (WAVELENGTH 465-490NM) AND EMITS YELLOW LIGHT (530NM)
INJECTED INTO PERIPHERAL VEIN TO CIRCULATE TO THE EYE
PASSES THROUGH SHORT POSTERIOR CILIARY ARTERY INTO THE CHORIOCAPILLARIS 8-12S POST INJECTION
THEN ENTERS RETINAL CIRCULATION
What are some side effects of fluoresence angiography?
URINE DISCOLOURATON
NAUSEA
VASOVAGAL SYNCOPE
ANAPHYLAXIS (RARE)
CONTRAINDICATED IF ALLERGIC TO SHELLFISH
FUNDUS CAMERA WITH COBALT BLUE EXCITATION AND YELLOW GREEN BARRIER USED TO CAPTURE IMAGES OF RETINA DURING PASSAGE OF DYE INTO THE POSTERIOR SEGMENT OF THE EYE
What is cyanine green angiography?
ICG IS 98% BOUND TO ALBUMIN IN THE PLASMA
LOW PERMEABILITY WHEN PASSING THROUGH CHOROID
USES NEAR-INFRARED LIGHT
THESE FACTORS ALLOW FOR BETTER VISUALISATION OF CHOROID VASCULATURE
When is cyanine green angiography contraindicated?
PREGNANCY AND WITH SEAFOOD / IODINE ALLERGIES
What is fundus autofluoresce?
NO USE OF DYE
DETECTS LIPOFUSCIN ALREADY PRESENT WITHIN THE RETINAL EPITHELIUM
CAN BE USED IN BEST DISEASE AND MONITORING GEOGRAPHIC ATROPHY
What are electrodiagnostic tests?
TESTS ELECTRICAL ACTIVITY OF THE RETINA IN RESPONSE TO A LIGHT STIMULUS
ELECTRO-OCULOGRAM REFLECTS THE ACTIVITY OF PHOTORECEPTORS AND RPE
RETINAL DISEASES PROXIMAL TO PHOTORECEPTORS GIVE NORMAL EOG READINGS
ERG AND EOG MAY BE USEFUL IN DIAGNOSING CONDITIONS SUCH AS BEST DISEASE AND RETINITIS PIGMENTOSA
What is tonometry (glaucoma)?
USED TO MEASURE IOP
MOST WIDELY USED: GOLDMANN APPLANTATION TONOMETRY IS THE MOST WIDELY USED
FOLLOWS IMBERT-FICK LAW TO ESTABLISH THE AMOUNT OF FORCE REQUIRED TO FLATTEN A CORNEAL AREA OF 3.06MM IN DIAMETER (ASSUMING CCT OF 520um
What can cause incorrect measurements in tonometry?
EXCESSIVE FLUOROSCEIN: OVERESTIMATION OF IOP
LOW OR HIGH CCT: UNDERESTIMATE / OVERESTIMATES IOP RESPECTIVELY
ASTIGMATISM
CALIBRATION ERRORS
What is gonioscopy?
USED TO DETERMINE WHETHER IRIDOCORNEAL ANGLE IS OPEN OR CLOSED
VISUALISATION OF ALL STRUCTURES INDICATES A WIDE OPEN ANGLE
INABILITY TO VISUALISE ANY STRUCTURES INDICATES A CLOSED ANGLE
What are the structures (ant–> pos) seen in gonioscopy?
SCHWALBE LINE
NONPIGMENTED TRABECULAR MESHWORK
PIGMENTED TRABECULAR MESHWORK:
- PIGMENTATION NOT PRESENT AT BIRTH
- INCREASES WITH AGE, USUALLY DURING PUBERTY
SCLERAL SPUR
-ANTERIOR PROTRUSION OF THE SCLERA THAT
MARKS THE ATTACHMENTS OF THE CILIARY BODY’S
LONGITUDINAL FIBRES
CILIARY BODY
What is perimetry?
USED TO DETECT VISUAL FIELD DEFECTS AND IS COMMONLY USED IN GLAUCOMA AND NEURO-OPTHALMIC CONDITIONS
EXAMPLES OF PERIMETRY:
HUMPHREY VISUAL FIELD ANALYSIS
GOLDMANN VISUAL FIELD TESTING
What is included in glaucomatous field defects?
NASAL STEP
PARACENTRAL DEPRESSION : MOST COMMONLY SUPERONASALLY
ARCUATE DEFECTS: COMBINATION OF PARACENTRAL DEPRESSIONS
RING SCOTOMA: SUPERIOR + INFERIOR ARCUATE DEFECTS
TUNNEL VISION WITH A TEMPORAL SPARING OF VISUAL FIELD
What investigations are used in neuro-Opthalmology and orbit?
MRI SCANS:
-ARE PRODUCED BY THE ALIGNMENT OF THE
HYDROGEN ATOMS
-USED TO AID IN DIAGNOSIS OF INTRACRNAIAL
LESIONS AFFECTING VISUAL PATHWAY
COMPUTED TOMOGRAPHY:
-SERIES OF X-RAY BEAMS TO FORMA DETAILED
IMAGE OF THE BODY
- QUICKER THAN MRI SO MORE VALUABLE IN ACUTE
SETTINGS
INDICATIONS:
ORBITAL FRACTURES
ORBITAL CELLULITIS
THYROID EYE DISEASE
CEREBRAL HAEMORRHAGES
CT ANGIOGRAPHY IS ALSO IMPORTANT TO
INVESTIGATE FOR SUBARACHNOID HAEMORRHAGE
AND INTRACRANIAL ANEURYSMS
What properties do all beams from lasers have?
COHERENCY (ALL EMITTED PHOTONS ARE IN THE SAME PHASE)
MONOCHROMACITY (SINGLE WAVELENGTH)
COLLIMATION (NARROW WITH MINIMAL DIVERGENCE)
What are the three principal parts of all lasers?
SOURCE OF ENERGY: LIGHT OR ELECTRICAL
A MEDIUM: CONTAINING ATOMS OR MOLECULES THAT UNDERGO STIMULATED EMISSION AND IS THE MAJOR DETERMINANT OF WAVELENGTH: GAS (ARGON, KRYPTON, CARBON DIOXIDE) LIQUID (E.G. DYES) SOLID (E.G. NEODYMIUM-DOPED YTTRIUM ALUMINIUM GARNET CRYSTALS
OPTICAL RESONATOR THAT USES MIRRORS TO
AMPLIFY LIGHT
Where is melanin found and what wavelengths does it absorb?
FOUND MAINLY IN RPE AND CHOROID, ABSORBS MOST OF THE VISIBLE SPECTRUM AND INFRARED WAVELENGTHS
Where is xanthophyll found and what wavelengths does it absorb?
PRESENT AT THE MACULA. ABSORBS BLUE LIGHT (450-495NM)
What wavelengths does haemoglobin absorb?
ABSORBS BLUE, GREEN (495-570NM) AND YELLOW LIGHT (570-590NM)
What is photovaporization?
VAPORIZATION OF WATER FROM TISSUES OCCURS IN TYPES OF LASERS SUCH AS CO2 LASERS AS THEY RAISE TEMPERATURE BEYOND 100 DEGREES
What is photocoagulation?
ABSOPRTION OF LASER EMISSION BY TISSUES CAUSES A RISE IN TEMPERATURE LEADING TO PROTEIN DENATURATION E.G. PANRETINAL PHOTOCOAGULATION USED IN DIABETES
How do photocoagulative lasers work?
ARGON BLUE-GREEN – ABSORBED BY MELANIN, HAEMOGLOBIN AND XANTHOPHYLL TF. NOT USED ON MACULA
KRYPTON RED (647NM): ABSORBED BY MELANIN
FREQUENCY DOUBLED Nd:YAG (532NM): ABSORBED BY HAEMOGLOBIN AND MELANIN IN THE RPE AND TRABECULAR MESHWORK
DIODE (810nm): EMITS NEAR-INFRARED RADIATION AND IS ABSORBED BY MELANIN
How do photochemical lasers work?
WORK BY BREAKING CHEMICAL BONDS THAT HOLD TISSUE TOGETHER USING ULTRAVIOLET LIGHT (PHOTOABLATION) E.G. EXCIMER LASER:
PHOTOREFRACTIVE KERATECTOMY: CORNEAL EPITHELIUM IS FIRST REMOVED THEN ABLATION USED TO RESHAPE THE CORNEA
LASER ASSISTED IN SITU KERATOMILEUSIS (LASIK): CORNEAL FLAP IS CREATED, STROMA IS THEN ABLATED TO RESHAPE CORNEA AND FLAP IS REPLACED
LASER EPITHELIAL KERATOMILEUSIS (LASEK SURGERY) - CORNEAL EPITHELIUM IS PEELED USING 20% ETHANOLD, LASER ABLATION IS PERFORMED AND EPITHLEIUM IS REPLACED
