Ocular radiology


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Ocular radiology

  1. 1. OCULAR RADIOLOGY Vijay Joshi
  2. 2. DISADVANTAGES OF EYE AS A SUBJECT OF RADIOLOGY 1. The globe does not have any bone or opaque landmark. 2. The orbit are irregular prismoids, walls are not parallel and size of all the walls is not similar. 3. Orbits are surrounded by air containing paranasal sinuses on three sides. 4. The occipital bone and apex of pterous bone encroach on true AP or PA view of orbit. 5. In lateral view findings of opposite side overlap findings of side of interest.
  3. 3.  So, it is customary to know the basics and advancements in ocular radiology to use the radiological modalities judiciously, logically which are economic to patient and prevent undue exposure of radiation to patient.  So, use the tools accordingly and logically and judiciously after a through history and examination.  Don’t jump on the investigations before work up.  The radiological modalities are there to support our diagnosis made clinically.  Here I made an attempt to put some light on ocular radiology which is generally not taken as a separate topic for learning.
  5. 5. Lateral view Lateral & Internal View
  7. 7. IMAGING IN OPHTHALMOLOGY  X-rays  Computed tomography  Three dimensional reconstruction  CT angiography  Magnetic resonance imaging  Magnetic resonance angiography  Magnetic resonance venography  Cerebral arteriography  Nuclear medicine  Ophthalmic ultrasonography i. A scan ii. B scan iii. Ultrasonographic biomicroscopy iv. Doppler ultrasonography o Dacryocystography
  8. 8. X RAYS  Wilhelm Röntgen German physicist discovered of X-rays in 1895.  Principle: Images of radiopaque tissues obtained by exposure of special photographic plates to ionizing radiation.  Uses in ophthalmology: 1. Used to identify or exclude radiopaque intraorbital or intraocular foreign bodies. 2. Plain films remain a valid screening modality before magnetic resonance imaging (MRI) if an occult metallic foreign body is suspected. 3. Plain films should not be used for the diagnosis of orbital fractures, as it give two dimensional images, some of the findings can be missed.
  9. 9. DIFFERENT X RAYS VIEWS IN OPHTHALMOLOGY  Lateral  Caldwell  Waters  Submentovertex  Rhese
  10. 10. LATERAL VIEW Side view of orbits and sinuses a, orbital roof; b, frontal sinus; c, ethmoid sinus; d, anterior clinoid process; e, sella turcica; f, planum sphenoidale
  11. 11. CALDWELL VIEW: OCCIPITO FRONTAL VIEW/ NOSE FOREHEAD POSITION • View taken with nose & forehead touching the film & X ray beam is projected 15- 25 degree caudally • Projects petrous portions of temporal bones just beneath the orbits  a, frontal sinus; b, innominate line; c, inferior orbital rim; d, posterior orbital floor; e, superior orbital fissure; f, greater wing of sphenoid;g, ethmoid sinus; h, medial orbital wall; i, petrous ridge; j, zygomatic-frontal suture; k, foramen rotundum
  12. 12. WATERS’ VIEW: OCCIPITO MENTAL VIEW/ NOSE- CHIN POSITION  View is taken in such a way that chin of the patient touch the film while Xray beam is projected from behind  Waters’ view with open mouth is preferred as it also shows sphenoid sinus.  In this view, petrous bones are projected below the maxillary antra. a, frontal sinus; b, medial orbital wall; c, innominate line; d, inferior orbital rim; e, orbital floor; f, maxillary antrum; g, superior orbital fissure; h, zygomatic-frontal suture; i, zygomatic arch
  13. 13. SUBMENTOVERTEX / BASAL PROJECTION a, zygomatic arch; b, orbit; c, lateral orbital wall; d, posterior wall of maxillary sinus; e, pterygoid plate; f, sphenoid sinus • This view is obtained with the patient's neck extended either in the supine or upright position. • The top of the head is placed so that the infraorbitomeatal line is parallel with the x-ray cassette. • The x-ray beam is directed at right angles to the infraorbitomeatal line.
  14. 14. RHESE VIEW/ OPTIC FORAMEN VIEW  The patient is positioned with the orbit to be studied against the x-ray cassette.  The zygoma, nose, and chin should touch the cassette.  The x-ray beam is directed posterior- anteriorly at 40 degrees to the midsagittal plane.  In this position the optic canal is in the inferolateral quadrant of the orbit and oriented perpendicular to the x-ray cassette. a, right optic canal; b, optic strut; c, superior orbital fissure; d, ethmoid sinus; e, planum sphenoidale; f, greater wing of sphenoid
  15. 15. APPLIED SKIAGRAM Soft tissue density (arrow) located in the roof of the maxillary sinus. Disruption of the orbital floor is seen at the fracture site Caldwell projection of a haemangioma of the left orbit. Soft tissue density is seen in the lateral orbit with partial calcification
  16. 16. APPLIED SKIGRAM Caldwell projection of a patient with a rhabdomyosarcoma. The superior orbital rim is involved (arrow) with erosion of bone that disrupts the continuity of the orbital margin. Plain x-ray reveals foreign body consistent with a pencil (2 arrows) seen in the medial part of the left orbit.
  17. 17. APPLIED SKIAGRAM Caldwell projection showing an optic nerve sheath meningioma of the left orbit. The increased radiodensity is caused by the calcium content of the meningioma Enlargement of the left superior orbital fissure (arrow) by neurofibromatosis. The Caldwell projection gives the best view of this fissure.
  18. 18. LOCALIZATION OF IOFB  Limbal ring method: It is the most simple but now-a-days, sparingly employed technique.  A metallic ring of the corneal diameter is stitched at the limbus and X-rays are taken.  One exposure is taken in the AP view.  In the lateral view three exposures are made one each while the patient is looking straight, upwards and downwards, respectively.  The position of the foreign body is estimated from its relationship with the metallic ring in different positions
  19. 19. LOCALIZATION OF IOFB Limbal ring used for localization of an intraocular foreign body. Limbal ring method of radiographic localization of IOFB: Lateral view with eyeball in straight position; superimposed over lateral view with eyeball in down gaze.
  20. 20. XRAY SKULL OF OPHTHALMIC INTEREST 1. For raised intracranial tension, silver beaten appearance (in case of papilledema). However, papilledema may occur in the absence of silver beaten appearance. 2. Intracranial calcification is seen in congenital toxoplasmosis, adenoma, meningioma, healed tubercular meningitis and craniopharyangioma. 3. Changes in pituitary fossa.
  21. 21. THE PITUITARY FOSSA IS EXAMINED FOR 1. Its size- enlargement is seen in pituitary tumors. 2. Suprasellar calcification 3. Double floor of sella 4. J- shaped pituitary fossa 5. Empty sella syndrome. 6. Destruction of posterior clinoid.
  22. 22. SUMMARY OF RADIOGRAPHIC PROJECTIONS AND STRUCTURES Projection Structures Pathology Waters · Orbital floor (anterior 2/3) · Blow-out fracture · Maxillary sinus · Maxillary sinus disease Caldwell · Frontal and ethmoid sinus · Sinus disease (mucocele) · Innominate line · Medial and lateral wall fracture · Sphenoid bone · Orbital floor (posterior 1/3) · Meningioma of sphenoid wing Lateral · Orbital roof · Orbital roof fracture · Sella turcica · Frontal sinus disease · Sinus air-fluid levels · Pituitary disease Basal/ Submentovertex · Sphenoid and ethmoid sinus · Sinus disease · Lateral wall fractures · Lateral wall of orbit · Zygomatic arch fractures · Zygomatic arch Optic foramen/ Rhese · Optic canal · Apex tumors · Optic nerve tumours
  23. 23. COMPUTED TOMOGRAPHY  Dr. Allan M. Cormack (1924-1998) and Godfrey N. Hounsfield (1919-2004) independently discovered and developed computer assisted tomography in the early 1970s. Got noble prize for same.  Principle:  CT uses ionizing radiation and computer-assisted formatting to produce multiple cross-sectional planar images.  The penetration of the ionizing radiation is measured in Hounsfield number / CT Value.  CT-values: contain the linear absorption coefficients of the underlying tissue in every volume element with respect to the μ-value of water.  Using this definition the CT-values of different organs are relatively stable and independent of the X-ray spectrum.  CT-value = (μ – μ water) / μ water x 1000 HU
  24. 24. Principle contd :  Since CT number values are strongly related to tissue densities the various tissues and materials are distributed along the scale according to their density.  It is this difference in densities that is the source of the physical contrast that will be converted and displayed as visible contrast in the images.  To a great extent, the very high contrast sensitivity of CT is derived from the ability to select a small range of CT numbers and display them over the full brightness range (dark black to bright white) in the image.  The range of CT numbers to be displayed in the image is designated as the WINDOW. The two adjustable protocol factors that control the window are the LEVEL and the WIDTH.
  25. 25.  Principle contd:  The LEVEL control sets the midpoint of the window range along the CT number scale. It can be used to optimize the image contrast for viewing different anatomical regions.  A relative low window might be used for seeing the contrast within the lungs and a high window to see contrast within bones.  The WIDTH setting is very much of an image contrast control. Reducing the window width increases the contrast among tissues as they are displayed in an image.
  26. 26. Hounsfield unit of different organs
  27. 27. METHOD 1. A motorized table moves the patient through a circular opening in the CT imaging system. 2. While the patient is inside the opening of the CT imaging system, an x-ray source and detector within the housing rotate around the patient. A single rotation takes about 1 second. The x-ray source produces a narrow, fan-shaped beam of x-rays that passes through a section of the patient's body. 3. A detector opposite from the x-ray source records the x-rays passing through the patient's body as a "snapshot" image. Many different "snapshots" (at many angles through the patient) are collected during one complete rotation. 4. For each rotation of the x-ray source and detector, the image data are sent to a computer to reconstruct all of the individual "snapshots" into one or multiple cross-sectional images (slices) of the internal organs and tissues
  28. 28. COMPUTER TOMOGRAPHY  Possible image planes include axial, direct coronal, reformatted coronal, and reformatted parasagittal images.  Bone and soft-tissue windows should always be reviewed in both axial and coronal orientations.  Orbital studies use 3-mm or thinner slices.  Radiopaque iodinated contrast allows more extensive evaluation of vascular structures and areas where there is a breakdown of the normal capillary endothelial barrier (as in inflammation).
  29. 29. ORBITAL ANATOMY ON CT SCAN 1. Zygomatic bone 2. Nasal septum 3. Lacrimal gland 4. Sclera 5. Vitreous body 6. Optic nerve 7. Medial rectus 8. Lateral rectus 9. Superior orbital fissure 10. Optic canal 11. Pituitary gland 12. Ethmoid sinus 13. Sphenoid sinus Sagittal view
  30. 30. ORBITAL ANATOMY ON CT SCAN 1. Optic nerve 2. Ophthalmic artery 3. Superior rectus 4. Inferior rectus 5. Medial rectus 6. Lateral rectus 7. Superior oblique 8. Ethmoid sinus 9. Maxillary sinus 10. Inferior turbinates 11. Zygomatic bone 12. Frontal bone Coronal view
  31. 31. USES IN OPHTHALMOLOGY 1.Excellent for defining bone abnormalities such as fractures (orbital wall or optic canal), calcification, or bony involvement of a soft-tissue mass. 2. Locating suspected intraorbital or intraocular metallic foreign bodies. Glass, wood, and plastic are less radiopaque and therefore more difficult to isolate on CT. 3. Soft-tissue windows are good for determining some pathologic features, including orbital cellulitis/abscess, noninfectious inflammation, and tumors. 4. May be useful in determining posterior scleral rupture when clinical examination is inconclusive, but B-scan ultrasonography may be more sensitive. 5. Excellent for imaging paranasal sinus anatomy and disease. 6. Head CT helpful for locating parenchymal, subarachnoid, subdural, epidural, and retrobulbar hemorrhage in either acute or subacute setting. 7. Imaging modality of choice for thyroid-related orbitopathy. 8. Any loss of consciousness requires CT of the brain. CT of the brain does not provide adequate detail of the orbital anatomy, and vice versa.
  32. 32. GUIDELINES FOR ORDERING AN ORBITAL STUDY  Always order a dedicated orbital study if ocular or orbital pathology is suspected. Always include views of paranasal sinuses and cavernous sinuses.  Order both axial and coronal views.  When evaluating traumatic optic neuropathy, request 1-mm cuts of the orbital apex and optic canal to rule out bony impingement of the optic nerve.  When attempting to localize ocular or orbital foreign bodies, order 1-mm cuts.  Contrast may be necessary for suspected infections or inflammatory conditions. Contrast is helpful in distinguishing orbital cellulitis from abscess. However, contrast is not mandatory to rule out orbital inflammation or postseptal involvement.  Relative contraindications for contrast include renal failure, diabetes, congestive heart failure, myeloma, sickle cell disease, multiple severe allergies, and asthma. Check renal function in patients in whom renal insufficiency is suspected.  Obtain pregnancy test before obtaining CT scans in females of childbearing age if possible.  CT scans may be obtained in children with careful consideration of the risk of radiation exposure versus benefits of performing the scan.  Each CT scan exposes children to radiation with a cumulative risk over their lifetime. Radiation exposure from CT scans in children is of particular concern when serial imaging is required. In these cases, MRI is often a better choice for children, although sedation may be needed.
  33. 33. APPLIED Coronal soft-tissue window shows a large blowout fracture of the orbital floor. This finding could have been missed on axial study, demonstrating the importance of reviewing both axial and coronal images. Axial soft-tissue window of inferior orbit shows abnormality, which is difficult to assess, picked easily by CT scan
  34. 34. THREE DIMENSIONAL RECONSTRUCTION o Contemporary CT scanners offer isotropic or near isotropic (uniformity in all orientations) resolution, display of images does not need to be restricted to the conventional axial images. o Instead, it is possible for a software program to build a volume by "stacking" the individual slices one on top of the other. The program may then display the volume in an alternative manner.  Multiplanar reconstruction  Typical screen layout for diagnostic software, showing one 3D and three MPR views  Multiplanar reconstruction (MPR) is the simplest method of reconstruction. A volume is built by stacking the axial slices. The software then cuts slices through the volume in a different plane (usually orthogonal). As an option, a special projection method, such as maximum-intensity projection (MIP) or minimum-intensity projection (mIP), can be used to build the reconstructed slices.  MPR is frequently used for examining the spine. Axial images through the spine will only show one vertebral body at a time and cannot reliably show the intervertebral discs. By reformatting the volume, it becomes much easier to visualise the position of one vertebral body in relation to the others.
  35. 35. THREE DIMENSIONAL RECONSTRUCTION  Modern software allows reconstruction in non-orthogonal (oblique) planes so that the optimal plane can be chosen to display an anatomical structure.  This may be particularly useful for visualising the structure of the bronchi as these do not lie orthogonal to the direction of the scan.  For vascular imaging, curved-plane reconstruction can be performed. This allows bends in a vessel to be "straightened" so that the entire length can be visualised on one image, or a short series of images.  Once a vessel has been "straightened" in this way, quantitative measurements of length and cross sectional area can be made, so that surgery or interventional treatment can be planned.
  36. 36. THREE DIMENSIONAL RECONSTRUCTION o Surface rendering  A threshold value of radiodensity is set by the operator (e.g., a level that corresponds to bone). From this, a three-dimensional model can be constructed using edge detection image processing algorithms and displayed on screen. Multiple models can be constructed from various thresholds, allowing different colours to represent each anatomical component such as bone, muscle, and cartilage. However, the interior structure of each element is not visible in this mode of operation.  Volume rendering  Surface rendering is limited in that it will display only surfaces that meet a threshold density, and will display only the surface that is closest to the imaginary viewer. In volume rendering, transparency and colours are used to allow a better representation of the volume to be shown in a single image. For example, the bones of the pelvis could be displayed as semi-transparent, so that, even at an oblique angle, one part of the image does not conceal another.  Image segmentation  Where different structures have similar radiodensity, it can become impossible to separate them simply by adjusting volume rendering parameters. The solution is called segmentation, a manual or automatic procedure that can remove the unwanted structures from the image.
  37. 37. THREE DIMENSIONAL RECONSTRUCTION Three-dimensional reconstruction of the maxillofacial skeleton showing gross destruction and displacement of the osseous structures Three-dimensional reconstruction of a malformation of Vein of GALEN
  38. 38. USES IN OPHTHALMOLOGY  In reconstructing orbit & skull during trauma.  The retinal reconstructions can be viewed as a whole,, but can also be viewed as segmented 3D volumetric objects through which specific structures can be viewed in isolation or subtracted from the object to improve visualization of remaining structures.  It also permits views of the retina from any angle, including from within the retinal tissue itself.  When viewed from non-conventional perspectives, retinal structures become more obvious, such as the interconnections of the cystic spaces in vitreomacular traction.  Manipulation of accurate 3D renderings may also provide more precise surgical planning.  Automated segmentation of OCT data sets can provide objective, accurate, and fast isolation of specific retinal layers or particular retinal structures.  These segmentation tools also permit quantitative analysis of specific retinal structures, as in the example of the volume measurements of the cystic spaces in vitreomacular traction.
  39. 39. APPLIED A three-dimensional rendering shows the cystic spaces and their relationship with the posterior hyaloid. The tractional forces exerted by the vitreous on the inner retina become apparent in this inferior- oblique view (blue arrows). An isosurface volumetric three- dimensional rendering reveals the cystic spaces (yellow) and the posterior hyaloid (blue) with the inner limiting membrane sandwiched in between (green). The green surface below the cysts represents the retinal pigment epithelium (RPE). Isosurface reconstruction portrayed the retinal surface corrugations caused by an epiretinal membrane. A ridge at the edge of the epiretinal membrane was not as obvious on the 2D OCT images
  40. 40. CT ANGIOGRAPHY  CT angiography (CTA) is helpful in diagnosing intracranial vascular pathology, including aneurysms.  It is available on all multidetector CT scanners and in general is more sensitive than magnetic resonance angiography (MRA).  However, it requires the use of intravenous iodinated contrast.
  41. 41. MAGNETIC RESONANCE IMAGING  Paul C Lauterbur and Peter Mansfield discovered the MRI.  Obtains multi planar images without loss of resolution.  Contrast studies can be ordered using gadolinium, a well- tolerated non–iodine-based paramagnetic agent.  Principle: MRI is based on the concept of nuclear magnetic resonance, in which the nuclei of certain atoms (H ions) become aligned or polarized when placed in a strong magnetic field.
  42. 42. Principle contd.. • In the absence of an external magnetic field, the spin orientation of free protons is random. • In a strong magnetic field, the free protons become aligned with their magnetic axis parallel (or, less often, antiparallel) to the magnetic field. • Exposure to a brief radiofrequency pulse at the Larmor frequency changes the alignment of the free protons' spin axes. • After the radiofrequency pulse, the free protons twirl like tops around the lines of force of the magnetic field with a motion called precession
  43. 43. PRINCIPLE CONTD..  When the RF pulse is switched off, the longitudinal magnetization increases and the transversal magnetization decreases or disappears.  The longitudinal relaxation is described by the time constant T1, the longitudinal or spin-lattice relaxation time; the transversal relaxation is described by the time constant T2, the transversal or spin-spin relaxation time.  T1 depends on tissue composition, structure, and surroundings and is an expression of the time it takes for the energy imparted by the RF pulse to be transferred to the lattice of atoms that surround the nuclei.  T2 comes about when protons go out of phase due to in homogeneities of the external and internal magnetic field and is an expression of the time it takes for the loss of coherent precession of the nuclei after the RF pulse.
  45. 45.  T1-weighted images are good for delineating ocular anatomy, as fluid appears dark (“black” vitreous, looks like high-definition CT scan) and fat appears bright.  Contrast-enhanced images are done with T1 weighting. T2-weighted images are best to discern pathology: fluid is bright (“white” vitreous).  As a rule, processes that are dark on CT are bright on T2.  Very intense tissue signals (fat in T1 -weighted images and cerebrospinal fluid, vitreous in T2-weighted images) may obscure subtle signal abnormalities in neighbouring tissues.  Special sequences have been designed to reduce these high signals.  Fat suppression techniques, such as short tau inversion recovery (STIR), are used to obtain relatively T1 -weighted images without the confounding bright fat signal.
  46. 46.  Fluid-attenuated inversion recovery (FLAIR) provides T2- weighted images without the high-CSF signal, making FLAIR ideal for viewing the periventricular white matter changes in a demyelinating process such as multiple sclerosis.  Diffusion-weighted imaging (DWI): Diffusion of water (H Ions) is seen across tissues, dec/ inhibited in stroke, inc in tumours.  Diffusion-weighted imaging (DWI) is sensitive to recent vascular perfusion alterations and is thus ideal for identifying recent infarction.  An abnormal DWI signal develops within minutes of the onset of cerebral ischemia and persists for approximately 3 weeks, serving as a time marker for acute and sub acute ischemic events .
  48. 48. SUMMARY OF MRI SEQUENCES Properties Usefulforintraorbital structuressuchasopticnerve, extraocularmuscles,and orbitalveins.Thestrongfat signalwithintheorbit gives poorresolutionoflacrimal glandandmayalsomask intraocularstructures. T1-weightedimageswith brightintraconalfat signalsuppressedinthe orbit,allowingforbetter anatomicdetail.Essential forallorbitalMRIs. A paramagneticagentthatdistributesinthe extracellularspaceanddoesnotcrossthe intactblood–brainbarrier.Gd-DTPAisbest forT1,fat-suppressedimages.Thelacrimal glandandextraocularmuscles“enhance” withGd-DTPA.EssentialforallorbitalMRIs. Neverordergadoliniumwithoutorderingfat suppressionfororbitalstudies. Suboptimal intraocularcontrast. Demyelinating lesions(e.g.,multiple sclerosis)arebright. InterpretationFatis bright(highsignal intensity).Vitreousand intracranialventriclesare dark. Vitreous andfataredark. Extraocularmusclesare brightafterGd-DTPAis administered. MostorbitalmassesaredarkonT1and becomebrightwithgadolinium enhancement.Notableexceptionsarelisted inTable14.3.2. Fluid-containing structuressuchas vitreousandCSFare bright.Melaninis dark. T1 Fat Suppression Gadolinium-DTPA T2
  49. 49. USES IN OPHTHALMOLOGY 1. Excellent for defining the extent of orbital/central nervous system masses. Signal-specific properties of certain pathology may be helpful in diagnosis. 2. Poor bone definition (e.g., fractures). 3. Excellent for diagnosing intracranial, cavernous sinus, and orbital apex lesions, many of which affect neuro-ophthalmic pathways. 4. For suspected neurogenic tumours (meningioma, glioma), gadolinium is essential in defining lesion extent. 5. All patients with clinical signs or symptomatic optic neuritis from suspected demyelinating disease should undergo brain MRI [fluid-attenuated inversion recovery (FLAIR) images are especially useful].
  50. 50. USES IN OPHTHALMOLOGY 6. Fat suppression should always be used in conjunction with intravenous gadolinium to enhance the visualization of the underlying pathology (e.g., optic neuritis, fat-containing lesions). 7. Diffusion-weighted imaging can help differentiate the various phases of cerebral infarction (e.g., hyper acute, acute, sub acute, and chronic).
  51. 51. GUIDELINES FOR ORDERING THE STUDY o Intravenous gadolinium is useful for augmenting ocular, orbital, and perineural masses.  In patients who have kidney failure, nephrogenic systemic fibrosis is a rare complication of gadolinium that occurs weeks to months after administration. It is characterized by a thickening and hardening of the skin, especially over extremities and trunk. There is no known proven therapy. Evaluate renal function in patients in whom renal insufficiency is suspected.  Contraindications to MRI: Severe claustrophobia, marked obesity, cardiac pacemakers, some cardiac valves, suspected magnetic intraocular/intraorbital foreign bodies, spinal stimulators, vagal nerve stimulators, stapes implants, and specific breast and penile implants. Titanium plates and newer aneurysm clips are MRI safe as are gold weights placed in the eyelids.  When in doubt, ask the radiologist to look up the specific device in an MRI safety catalog. Any patient with a poorly documented implanted device should NOT be scanned with MRI.
  53. 53. FEATURES OF CT VERSUS MRI CT MRI Better for bony lesions Better for soft tissue delineation Sensitive to acute hemorrhage Insensitive Chronic hemorrhage may be subtle Well seen 60% Acute strokes visualized 80% Acute strokes visualized Posterior fossa degraded by artifact Well visualized Poor resolution of demyelinating lesions Demyelinating lesions well seen at all stages Metal artifacts (skull plates, clips) Ferromagnetic artifacts Axial and coronal images Axial, coronal, sagittal, and angled images Iodinated contrast agent Paramagnetic contrast agent Risk: ionizing radiation Risk: magnetic field
  56. 56. APPLIED Axial T-1-weighted image without fat suppression or gadolinium. The vitreous is dark (hypointense) relative to the bright signal from fat. A well- circumscribed mass is clearly visible in the right orbit, also hypointense. Most orbital lesions are dark in T1 prior to gadolinium injection Axial T-1 image with fat suppression and gadolinium. Note how both the vitreous and fat are dark, but the extraocular muscles become bright. The orbital mass is now clearly visible. This technique should be performed in all orbital MRIs.
  57. 57. APPLIED Axial T-2-weighted image. The vitreous is hyperintense (bright) relative to the orbital fat. The lesion is also bright but in some cases may be isointense with the surrounding fat. MRI with FLAIR sequence of demyelinating lesions in multiple sclerosis.
  58. 58. MAGNETIC RESONANCE ANGIOGRAPHY  Principle: Signal from flowing blood is augmented while signal from stationary tissues is suppressed. MRA allows for three-dimensional rotational reconstruction.  Uses in ophthalmology: 1. Suspected carotid stenosis, occlusion, or dissection. 2. Suspected intracranial and orbital arterial aneurysms (e.g., pupil involving third cranial nerve palsy), AV malformations, and acquired AV communications. 3. Suspected orbital or intracranial vascular mass. 4. MRA is best for imaging high-flow and large calibre lesions. 5. Lower-flow lesions (e.g., varix) are not well seen. 6. MRA also has limited potential in visualizing cavernous sinus fistulas; colour Doppler studies and conventional arteriography are more sensitive in making this diagnosis.
  59. 59. GUIDELINES FOR ORDERING THE STUDY  Cerebral arteriography remains the gold standard for diagnosis of vascular lesions but carries significant morbidity and mortality in certain populations.  Currently, the limit of MRA is an aneurysm larger than 2 mm. However, the sensitivity is highly dependent on several factors: hardware, software, and the experience of the neuroradiologist.  Despite these potential limitations, MRA remains a safe and sensitive screening test, especially when coupled with MRI for concomitant soft-tissue imaging.  CTA in many situations can provide a suitable replacement for conventional angiography
  60. 60. APPLIED A. T1- and (B) T2-weighted MR scans demonstrate a moderately well- circumscribed intraconal mass enveloping the optic nerve. The lesion is hyperintense to vitreous on the T1-weighted scan. A fluid-fluid level (arrow) and patchy hypointense areas are seen within the mass on T2-weighted scan due to the presence of subacute blood products. C and D. Postcontrast fat- suppressed T1-weighted scans demonstrate no significant enhancement within the lesion, although there is minimal peripheral enhancement in surrounding orbital tissues.
  61. 61. MAGNETIC RESONANCE VENOGRAPHY  Magnetic resonance venography is helpful in diagnosing venous thrombosis.  MRI and magnetic resonance venography are an essential part of the workup of any patient presenting with bilateral optic disc swelling MRV of sinus thrombosis
  62. 62. CEREBRAL ARTERIOGRAPHY  Principle: Intra-arterial injection of radiopaque contrast in carotid artery followed by rapid-sequence x-ray imaging of the region of interest to evaluate the transit of blood through the regional vasculature.  Unlike MRA or CTA, catheter arteriography allows the option of simultaneous treatment of lesions by intravascular techniques.  Arteriography is the gold standard for diagnosing intracranial aneurysms but is being replaced in many centres by CTA.
  63. 63. USES IN OPHTHALMOLOGY  Suspected arteriovenous malformations, carotid cavernous fistulas, cavernous sinus fistula, and vascular masses (e.g., hemangioma, varix).  Evaluation of ocular ischemic syndrome or amaurosis fugax due to suspected atherosclerotic carotid, aortic arch, or ophthalmic artery occlusive disease. Usually carotid Doppler US, MRA, or CTA is adequate for diagnosis.  Contraindication: In patients with suspected carotid artery dissection (catheter placement may propagate the dissection).
  64. 64. APPLIED Cerebral angiography images show a left CCF fed by the bilateral internal and external carotid arteries. A: Lateral arteriogram of left external carotid artery. B: Lateral arteriogram of left internal carotid artery. C: Anteroposterior arteriogram of right internal carotid artery. D: Magnetic resonance images indicate a prominent superior ophthalmic vein
  65. 65. NUCLEAR MEDICINE  Principle:  Nuclear medicine imaging uses radioactive contrast (radionuclide) that emits gamma radiation, which is then gathered by a gamma ray detector.  The classic types of radionuclide scanning known to ophthalmologists include bone scanning, liver–spleen scanning, and gallium scanning.
  66. 66. USES IN OPHTHALMOLOGY 1. Scintigraphy (e.g., with technetium-99): Useful for assessing lacrimal drainage physiology in patients with contradictory or inconsistent irrigation testing. 2. Systemic gallium scan: Useful for detecting extraocular sarcoidosis and Sjogren syndrome. 3. Technetium 99m-tagged red blood cell study: Occasionally used to distinguish cavernous hemangioma/hemangiopericytoma from other solid masses in the orbit. 4. PET: The use of PET for the diagnosis and management of orbital disease is still an evolving technique. Limitations in this area include the high background metabolic activity of the adjacent brain which may mask orbital abnormalities, the size of the orbital pathology (current PET scanners have a resolution of about 7 mm), and the relatively indolent nature of most orbital lymphomas (decreasing the intensity of the signal on PET).  PET is extremely useful in the diagnosis and surveillance of systemic pathologies, including lymphoma and metastases, and at present, this remains the primary role of PET in the management of orbital disease.
  67. 67. APPLIED Scintigraphy Nuclear lacrimal scintigraphy shows passage of tracer in the right lacrimal system but obstructed drainage in the left nasolacrimal duct
  68. 68. OPHTHALMIC ULTRASONOGRAPHY  Principle: A-scan, or amplitude-modulated ultrasound (US), uses ultrasonic waves (8 to 12 MHz) to generate linear distance versus amplitude of reflectivity curves of the evaluated ocular and orbital tissues.  A-scans are one dimensional and used for measuring and characterizing the composition of tissues on the basis of the reflectivity curves. Not all A-scan instruments are standardized.
  69. 69. NORMAL A-SCAN
  70. 70. A-SCAN  In A-scan , one thin, parallel sound beam is emitted from the probe tip at its given frequency of approximately 10 MHz, with an echo bouncing back into the probe tip as the sound beam strikes each interface.  An interface is the junction between any two media of different densities and velocities, which, in the eye, include the anterior corneal surface, the aqueous/anterior lens surface, the posterior lens capsule/anterior vitreous, the posterior vitreous/retinal surface, and the choroid/anterior scleral surface.
  71. 71. A-SCAN  The echoes received back into the probe from each of these interfaces are converted by the biometer to spikes arising from baseline  The greater the difference in the two media at each interface, the stronger the echo and the higher the spike.  If the difference at an interface is not great, the echo is weak and the displayed spike is short (eg, vitreous floaters, posterior vitreous detachments).
  72. 72. A-SCAN  No echoes are produced if the sound travels through media of identical densities and velocities, eg, young, normal vitreous or the nucleus of a noncataractous lens, in which the A-scan display goes down to baseline.  In the case of a cataractous lens, multiple spikes occur within the central lens area as the sound beam strikes the differing densities within the lens nucleus.  This spike height, or amplitude, is therefore what gives the information on which to base the quality of the measurements.
  73. 73. A-SCAN  Gates are electronic calipers on the display screen that measure between two points.  Biometers are designed so that between each pair of gates a measurement is rendered.  Gates should be readily visible for accurate editing of the scans, because if any one of them is aligned along an incorrect spike the entire eye length measurement will be erroneous.  The biometer automatically places a gate on what it believes to be the corneal spike, the anterior lens spike, the posterior lens spike, and the retinal spike, and it is programmed to measure the distance between each pair of gates at a given velocity.
  74. 74. A-SCAN  Ultrasound is measured based on how long it takes the sound to travel from one point to the next at a given velocity  The formula, Distance = velocity X time is programmed into biometers to calculate the distance between each pair of gates
  75. 75. A-SCAN  Then, the formula is divided by 2 because the sound also must echo back into the probe tip.  By selecting the eye type in the measurement mode (phakic, aphakic, or pseudophakic), the equipment is instructed to use this distance formula with the proper velocities between each gate pair for that particular eye type.
  76. 76. A-SCAN  When the machine is set for phakic average, only 2 gates are present, measuring the total eye at its average velocity of 1550 m/s.  The 2 gates should align along the corneal surface and the retinal surface, respectively.  The disadvantages to this setting are that:  The anterior chamber depth and the lens thickness cannot be monitored  The average sound velocity of 1550 m/s is only accurate through an average length eye. In eyes that are shorter or longer than average, this method of measuring produces an innate error.
  77. 77. SOUND VELOCITIES FOR EYE LENGTH MEASUREMENTS  Cornea  Aqueous/ Vitreous  Lens  Silicone oil  Aphakia  Phakia  1641m/s  1532m/s  1641m/s  980 – 1040m/s  1532m/s  1550m/s
  78. 78. A SCAN METHODS  Applanation technique  Applanation hand held technique  Using hand held ultrasound transducer probe  Stand held technique  Probe is fitted in place of tonometer in a S/L
  79. 79. A SCAN METHODS  Sound velocity of ultrasound beam must correspond with the phakic status of the patients  Pt has to be cooperative with steady fixation of gaze  TA is instilled  Tears & solutions should be wiped off from eyes  Patients is provided with fixation point at a far distance  Approach the eye slowly with transducer aligned to the optical axis
  80. 80. A SCAN METHODS  Probe is moved forward till it touches the cornea & instrument display show corneal contact  Probe is taken back very slightly until contact is broken & then reestablish contact with least amount of pressure that produces a display  This avoids compressing the cornea  At least 3 scan readings are obtained in each eye within 0.15mm of one another  Gain is set at lowest level at which good reading can be obtained
  81. 81. CHARACTERISTIC OF A GOOD A-SCAN  A tall echo from the cornea  One peak with contact probe  Double peaked echo with an immersion probe  Tall echoes from anterior and posterior lens capsule  Tall, sharply rising echo from retina  Medium tall to tall echo from sclera  Medium to low echoes from orbital fat
  82. 82. CHARACTERISTIC OF A GOOD A-SCAN  If difficult to get all five criteria, concentrate more on posterior echo  At least a tall retinal echo that rises at 90deg from baseline & has no stair steps on the leading edge  If not then think of –  Either the probe is not perpendicular to retina leading to short AL, or  There is some pathology interfering with A scan – like post Vit membrane, haemorrhage, staphyloma.  There should be appropriate echoes from sclera and orbital fat  If these echoes are missing, this means the sound is reflecting off the ONH rather than retina
  83. 83. HOLLADAY’S CRITERIA FOR SUSPECTING INACCURATE MEASUREMENT  Repeat measurements if:  AL <22.0 mm or >25.0 mm  Average corneal power < 40D or >47 D  Calculated emmetropia implant power is more than 3D from the average for the specific style* used.  Between eyes the difference in  Average corneal power > 1D  AL > 0.3 mm  Emmetropic implant power > 1D  * The avg emmetropic implant power for a specific lens style calculated using Holladay’s “ surgeon factor”: corneal power of 43.81 D & AL of 23.5 mm.
  84. 84. A SCAN METHODS  Applanation technique  Advantage: Disadvantage:  Convenient Corneal compression  Portable Abrasion of cornea less accurate in  Lens expensive short eyes
  85. 85. A SCAN METHODS  Immersion technique  Has better reproducibility  It is more accurate than applanation  Typical accuracy for AL measurement is within 0.12mm  It corresponds to postoperative refractive error of 0.28 D in an eye of average AL  It may display an AL longer than applanation  But as there is no compression of cornea it is equal to true axial length
  86. 86. A SCAN METHODS  Immersion technique  C/as water bath method,  patients is supine  Scleral shell is placed between the lids and centered over cornea  Scleral shell is filled with goniosol and dacriose  Ultrasound probe is suspended in scleral shell  Align the ultrasound beam with the macula by asking the pt to fix at the fixation light in the probe
  87. 87. A SCAN METHODS  Modified immersion technique  Aqueous & vitreous ultrasound velocity is 1532m/sec  Only cornea and lens has different velocity  If an eye is measured at an ultrasound velocity of 1532m/sec , a corrected axial length factor (CALF) of 0.32 mm is added to the apparent axial length which will give a true axial length TAL = AAL 1532 + 0.32 mm
  88. 88. A SCAN METHODS  Immersion technique  Advantages:  No risk of inaccurate reading from excess pressure applied  No risk of corneal abrasions  Disadvantage:  Cumbersome procedure  Supine position  Difficult to master
  89. 89. A SCAN METHODS Immersion vector A & B scan  Prevents corneal compression  Two-dimensional B-scan display helps guide superimposed A scan for measurement directly through macula  Horizontal axial A scan is taken so that vector passes through cornea, lens & fovea  Particularly important in eyes with posterior staphyloma
  90. 90. A & B Scan
  91. 91. FORMULAE FOR CALCULATING IOL POWER  Depending upon the basis of their deviation, the various formulae for calculating IOL power have been grouped into:  Theoretical formulae, &  Regression formulae  Based on the time when they evolved & the corrections incorporated into them, they have been grouped into:  First generation formulae  Second generation formulae  Third generation formulae  Fourth generation formulae
  92. 92. FIRST GENERATION FORMULAE  I. Theoretical Formulae:  Based on geometric optics, keratometry,and axial length  An assumed value for postoperative ACD was used in all the formulas  Changing the ACD by some amount in myopic, emmetropic and hypermetropic eyes causes different variation in lens power required for emmetropia.
  93. 93. THEORETICAL FORMULAS  Optimized theoretical formulas  Contains four assumed values –  Postoperative ACD  Corneal refractive index  Aqueous & vitreous refractive index  AL retinal thickness correction  These four values were optimized for the eyes to determine the maximum accuracy of this type of formula
  94. 94. THEORETICAL FORMULAS  At the IOL  Light must have a vergence equal to the dioptric value of the distance (A –K) between the IOL & the retina if the focus is to fall on retina  Since IOL is not in air the distance (A – K) must be divided by N  The dioptric value of this = N/(A – K)
  95. 95. THEORETICAL FORMULAS  Vergence power in the plane of the IOL will be combined effect of the refractive power of the IOL & the cornea  Effective power of lenses(F2) = F1/(1-dF1)  Substituting Pc for F1 and K/N for d  So,  Effective power of cornea in plane of the IOL will be = Pc/1- Pc.K/N
  96. 96. THEORETICAL FORMULAS  Therefore,  Required IOL = required vergence – effective  power in plane of IOL power of K  = N - Pc A – K 1 – Pc.K N
  97. 97.  A few of the 1st gnx theoretical formulae are: 1. Binkhorst formula:  P = 1336( 4r-a) (a-d)(4r-d) Where P is IOL power in diopters, r- corneal radius in mm, a – AL in mm, d- assumed postoperative ACD plus corneal thickness. 2. Colenbrander –Hoffer formula 3. Gill’s formula 4. Clayman’s formula 5. Fyodorov formula
  98. 98. DRAWBACKS  Tend to predict too large an emmetropic value in short eyes (less than 22 mm) and too small a value in long eyes (more than 24.5 mm)  They are too cumbersome to apply without the assistance of a calculator or a computer  Require guess about ACD & results depends on the accuracy of that guess.  Most of these formulae were developed for iris suported lenses. So, the estimate for the distance between the cornea and the implant (post op ACD) are diff for presently used PCIOL’s
  99. 99. II. REGRESSION FORMULAE  Based on regression analysis of actual postoperative results of implant power as a function of the variables of corneal power and axial length  A best fit line or a curve is plotted from the known axial lengths & keratometric readings and is subsequently used to predict the implant power needed for other patients
  100. 100. SRK-I FORMULA  Introduced by Sanders, Retzlaff and Kraff  Taking into account the retrospective computer analysis of large number of postoperative refraction  ACD was replaced by constant (A) dependent on type of implant.  A constant is determined empirically for each implant  The technique uses multiple regression analysis that estimates the relationship between a dependent variable (residual refractive error) and a set of independent variable (preoperative AL, K, power of lens implanted)  A constant is greater the closure the lens implant is to the retina.  So, greatest with PCIOL, intermediate with iris fixated IOL and least with ACIOL.  It can be calculated for individual surgeon.
  101. 101. SRK-I FORMULA  P = A – 2.5L – 0.9K  A – constant specific for each lens  L – AL  K – average keratometry in dioptres  Good for eyes with AL between 22 & 24.5 mm  Predicts too small a value in short AL  Too large a value in long AL  To address this problem SRK-II was developed
  102. 102. 2ND GENERATION FORMULAE I. Theoretical formula i) Modified binkhorst formulae II. Regression formulae i) SRK II formula: A constant is modified on basis of AL as follows:  A constant is modified on the basis of AL:  If L is < 20 mm : A + 3.0  If L is 20-20.99 : A + 2.0  If L is 21 – 21.99 : A + 1.0  If L is 22 – 24.5 : A  If L is > 24.5 : A – 0.5
  103. 103. ii.) Modified SRK II formula: A constant is modified as given:  If L is < 20 mm: A + 1.5  If L is 20-21mm: A + 1.0  If L is 21-22 mm: A + 0.5  If L is 22.0- 24.5 mm A  If L is 24.5-26.0 mm A – 1.0  If L is > 26 mm A – 1.5
  104. 104. THIRD GENERATION FORMULAE  Most of the third generation formulae are a hybrid of both theoretical and regression( empirical ) formulae. I. Holladay-I formula II. Holladay II formula: more accurate because of its enhanced ability to predict the position of the implants. III. Hoffer’s formula: optimized with regression techniques for ACD. This formula performs best for short eyes. IV. Haigis formula: recent formula is a recent addition in the list of IOL power calculating formulae.
  105. 105. FOURTH GENERATION FORMULAE I. Holladay II formula: fourth generation theoretical formula optimized with regression technique for ACD. II. Holladay consultant IOL program: uses Holladay II formula with seven variables.
  106. 106. SRK/T FORMULA  A nonlinear theoretical optical formula  Optimized for postoperative anterior chamber depth, retinal thickness, & corneal refractive index  More accurate for extremely long eyes (> 28mm)  The AL as measured with ultrasound is actually slightly short of the optical AL  D/t – distance is measured from anterior surface of cornea to the VR interface  So a retinal thickness correction factor are added  Retinal thickness correction factor = (0.65 – 0.02)AL  Correction factor is larger in short eyes & smaller in long eyes
  107. 107. FACTORS AFFECTING IOL CALCULATION  AL measurement –  Difference in AL measurement of 0.1mm can cause an error of 0.3 D in calculated IOL power  Source of error:  Corneal indentation during procedure  Improper equipment calibration  Failure to recognize the appropriate pattern of echoes  Anatomical thickness of retina
  108. 108. FACTORS AFFECTING IOL CALCULATION  AL measurement –  Clues to inaccurate AL measurement include:  A significant discrepancy between the two eyes  AL inconsistent with the patients refraction  Keratometry - improper calculation  Ultrasound velocity –  AL correction for retinal thickness
  109. 109. USES IN OPHTHALMOLOGY 1. Primary use in ophthalmology is measurement of axial length of the globe. This information is critical for intraocular lens (IOL) power calculations for cataract surgery.  Axial length information can also be used to identify certain congenital disorders such as microphthalmia, nanophthalmos, intraocular tumor size, intrinsic tumor vascularity, and congenital glaucoma. 2. Diagnostic identification of the echogenicity characteristics of masses in the globe or orbit with standardized A-scan probe. 3. Specialized A-mode ultrasonography can be used for corneal pachymetry (measurement of corneal thickness).
  110. 110. GUIDELINES FOR ORDERING THE STUDY  When used for IOL power calculations, make sure to check both eyes. The two eyes should be within 0.2 mm of each other.  Spikes along the baseline should be sharply rising at 90 degrees.  If needed, keratometry readings should be obtained prior to scan or 30 minutes after the scan for accurate results.
  111. 111. B SCAN  B-scan, or brightness-modulated US, gives real-time, two- dimensional (cross-sectional) images of the eye posterior to the iris to the posterior aspect of the globe.  Both contact and water-bath techniques may be used, but the contact method does not visualize the anterior chamber well.
  112. 112. B-SCAN  Differs from A-scan in that it produce a two- dimensional acoustic section by using both the vertical & horizontal dimensions of the screen to indicate configuration & location  A section of tissue is examined by an oscillating transducer that emits a sound beam that slices through the tissue  It requires a focused beam  Echoes are represented as dots  Strength of echo is depicted by the brightness of the dot
  113. 113. B-SCAN PROBE  Probe contains a transducer that moves rapidly back & firth near the tip of the probe  Each probe has a marker that indicates the side of the probe that is represented on the upper portion of the B-scan screen  Probe face is always represented by the initial line on the left side of the echogram
  114. 114. B-SCAN PROBE  The fundus located on the side of the globe opposite the probe,is represented on the right side of the echogram  Center of the screen corresponds to the central portion of probe face  Since this provides the best resolution, a lesion should always be centered within the echogram  The particular section of ocular tissue displayed on the screen depends on how the probe is positioned & how the marker is directed
  115. 115. 3 BASIC PROBE ORIENTATIONS  Transverse  Longitudinal  Axial
  116. 116. TRANSVERSE SCAN  Probe is placed on the globe with the longest diameter of the oval probe face positioned parallel I.e tangential to the limbus  The sound beam oscillates back & forth across the opposite fundus producing a circumferential slice  This orientation is appropriate for showing the lateral extend of the lesion
  117. 117.  Designation of the transverse scan is determined by the meridian that lies in the middle of the scanning section (probe centered at 6-o’clock will display the 12-o’clock meridian)  By convention –  Horizontal transverse scan (6 & 12-o’clock) are performed with the marker oriented towards the nose  Vertical scan (3 & 9-o’clock) are performed with marker directed superiorly
  118. 118. LONGITUDINAL SCANS  Probe is placed peripheral to limbus  Probe is rotated 90* from the position of the transverse scan so that the longest diameter of the probe face is perpendicular to limbus  Sound beam sweeps along the meridian opposite the probe rather than across the meridian  Longitudinal scan shows the anteroposterior extent of the lesion
  119. 119.  Marker is always directed towards the center of the cornea, regardless of which meridian is being examined  This produces an echogram with the optic disc & posterior fundus displayed on the lower portion of the screen  Whereas the peripheral globe is displayed superiorly
  120. 120. AXIAL SCANS  Performed with probe centered on cornea  Sound beam is directed through the center of the lens & the optic nerve  Displays lens & optic nerve in the center of the echogram
  121. 121. HORIZONTAL AXIAL SCAN  The marker is oriented towards the nose which places the macular region just below the optic disc  Vertical axial scan –  Marker is facing superiorly
  122. 122. AXIAL SCANS  Performed with probe centered on cornea  Sound beam is directed through the center of the lens & the optic nerve  Displays lens & optic nerve in the center of the echogram
  123. 123.  Horizontal axial scan –  The marker is oriented towards the nose which places the macular region just below the optic disc  Vertical axial scan –  Marker is facing superiorly
  124. 124. B-SCAN SCREENING TECHNIQUE  Superior half of globe –  Pts gaze directed superiorly  Probe is horizontally with its face next to inferior limbus & centered on the 6-o’clock meridian with marker directed nasally  Probe is gradually shifted towards the lower fornix
  125. 125.  Nasal portion –  Pt looks medially  Probe in a vertical orientation, with probe face centered near the temporal limbus  Again the probe is shifted from the limbus to fornix
  126. 126. EVALUATION OF MACULA  4 positions  Horizontal axial  Vertical transverse  Longitudinal  Vertical macula
  127. 127. USES IN OPHTHALMOLOGY 1. Define ocular anatomy in the presence of media opacities (e.g., mature cataract, hyphema, corneal opacity, vitreous hemorrhage, trauma) to evaluate retinal and/or choroidal pathology. 2. Diagnosis of scleral rupture posterior to the muscle insertions or when media opacities prevent direct visualization. 3. Identify intraocular foreign bodies especially if made of metal or glass (spherical objects have a specific echo shadow); wood or vegetable matter has variable echogenicity; can also give a more precise location if the foreign body is next to the scleral wall. 4. Evaluation of intraocular tumor/mass consistency, retinal detachment, choroidal detachment (serous vs. hemorrhagic), and optic disc abnormalities (e.g., optic disc drusen, coloboma).
  128. 128. GUIDELINES FOR ORDERING THE STUDY • If used in the setting of trauma to determine unknown scleral rupture, the probe is used over closed eyelids with immersion in copious amounts of sterile methylcellulose, such that no pressure is placed on the globe. The gain must be set higher to overcome the sound attenuation of the eyelids. Known ruptured globe is a relative contraindication to B-scan US. • When scleral integrity is not in question, B-scan US should be performed dynamically to help differentiate pathologic conditions, such as retinal detachment versus posterior vitreous detachment. • Dense intraocular calcifications (such as those occurring in many eyes with phthisis bulbi) result in poor-quality images. • Silicone oil and intraocular gas in the vitreous cause distortion of the scanned image, and therefore the study should be performed in an upright patient.
  129. 129. ULTRASONOGRAPHIC BIOMICROSCOPY  Principle: Ultra–high-frequency (50 MHz) B-mode US of the anterior one-fifth of the globe to give cross sections at near-microscopic resolution. Uses a water-bath eyelid speculum with viscous liquid in the bowl of the speculum. Normal anterior ultrasonographic biomicroscopy
  130. 130. USES IN OPHTHALMOLOGY 1. Excellent for defining corneoscleral or limbal pathologic conditions, anterior chamber angle, ciliary body, pathologic iris conditions (e.g., ciliary body masses/cysts, plateau iris, location of IOL), and small anterior foreign bodies. 2. Unexplained unilateral angle narrowing or closure. 3. Suspected cyclodialysis. o Guidelines for Ordering the Study o Known ruptured globe is a contraindication to the study.
  131. 131. DOPPLER ULTRASONOGRAPHY  Principle: A Doppler ultrasound test uses reflected sound waves to see how blood flows through a blood vessel.  It helps doctors evaluate blood flow through major arteries and veins, such as those of the arms, legs, and neck.  It can show blocked or reduced blood flow through narrowing in the major arteries of the neck that could cause a stroke.  Technique: During Doppler ultrasound, a handheld instrument (transducer) is passed lightly over the skin above a blood vessel.  The transducer sends and receives sound waves that are amplified through a microphone. The sound waves bounce off solid objects, including blood cells.  The movement of blood cells causes a change in pitch of the reflected sound waves (called the Doppler effect). If there is no blood flow, the pitch does not change.  Information from the reflected sound waves can be processed by a computer to provide graphs or pictures that represent the flow of blood through the blood vessels. These graphs or pictures can be saved for future review or evaluation
  132. 132. USES IN OPHTHALMOLOGY 1. Superior ophthalmic vein pathology: High-flow cavernous sinus fistulas, superior ophthalmic vein thrombosis. 2. Orbital varix. 3. Arteriovenous malformations. 4. Vascular disease including central retinal artery occlusion, central retinal vein occlusion, ocular ischemic syndrome, and giant cell arteritis.
  133. 133. APPLIED Colour Doppler of orbital capillary haemangioma. Multiple vascular channels showing moderate to high flow (blue and red)
  134. 134. DACRYOCYSTOGRAPHY  Principle: Involves the injection of radio-opaque contrast medium into the canaliculi followed by capture of magnified images.  The test is usually performed on both sides simultaneously.  A DCG is not necessary if the site of obstruction is obvious such as in the case of a regurgitating mucocele.  It should also not be performed in a patient with acute dacryocystitis
  135. 135. TECHNIQUE  The inferior puncta are dilated.  Plastic catheters are inserted into the inferior canaliculi on either side; alternatively the upper puncta may be used.  Contrast medium, usually 1–2 mL of Lipiodol, is simultaneously injected on both sides and postero-anterior radiographs are taken.  Ten minutes later an erect oblique film is taken to assess the effect of gravity on tear drainage. Digital subtraction DCG provides a higher quality image capture than conventional.
  136. 136. USES IN OPHTHALMOLOGY 1. Suspected nasolacrimal drainage obstruction. 2. May be used for defining lacrimal drainage system anatomy when the cause of obstruction is mal development, tumor, or even lacrimal stones with visualization of bony landmarks. 3. May be helpful in determining lacrimal pump function
  137. 137. APPLIED Dacryocystography (DCG) (A) Conventional DCG without subtraction shows normal filling on both sides; (B) normal left filling and obstruction at the junction of the right sac and nasolacrimal duct; (C) digital subtraction DCG shows similar findings
  138. 138. PLAY SAFE