Introduction• Ultrasound biomicroscopy (UBM) provides high- resolution imaging of the anterior segment in a noninvasive fashion.• In addition to the tissues easily seen using conventional methods (ie, slit lamp), such as the cornea, iris, and sclera, structures including the ciliary body and zonules, hidden from clinical observation, can be imaged and their morphology assessed.• Pathophysiologic changes involving anterior segment architecture can be evaluated qualitatively and quantitatively.
INTRODUCTION• Recent technique to visualize anterior segment with the help of high frequency ultra sound transducer.• UBM (anterior segment ultrasonography) is performed with a 50 Mhz probe.• The resolution of 50 MHz probe is 40 microns and the depth is 4 mm
• UBM is done with the patient in the supine position and the eye is open.• Since the piezoelectric crystal of the transducer is open it should not come in direct contact with the eye to prevent injury to the cornea
• There is a special cup which fits in between the eyelids, keeping them open• The eye cup is filled with saline or sterile methylcellulose.• The crystal of the transducer is placed in saline approximately 2 mm from the eye surface. (This distance of 2 mm prevents injury to the cornea and also helps as a fluid standoff.)• The eye is scanned in each clock hour from the center of the cornea to the ora serrata
Iridociliary cyst The most common clinical presentation of an irido-ciliary cystis a peripheral iris elevation - the typical UBM finding of a thinwalled structure with no internal reflectivity is diagnostic.
• UBM is useful in opaque media• The most important limitation of UBM is depth. UBM cannot visualize structures deeper more that 4 mm from the surface.• The other limitation is that UBM cannot be performed in presence of an open corneal or scleral wound.• It is time consuming
• Tomographic techniques generate slice images of three-dimensional objects.• Optical tomographic techniques are of particular importance in the medical ﬁeld, because these techniques can provide non- invasive diagnostic images
• Optical coherence tomography is a non- contact, real-time technique that uses low infrared laser energy to image structures.
• Optical coherence tomography imaging is based on measuring the delay of light (typically infrared) reflected from tissue structures.• Because light travels extremely fast, it is not possible to directly measure the delay at a micron resolution. Therefore, OCT employs low-coherence interferometry to compare the delay of tissue reflections against a reference reflection.
• To obtain an OCT image, the instrument scans a light beam laterally, creating a series of axial scans (A-scans), after which it combines these A-scans into a composite image.• Each A-scan contains information on the strength of reflected signal as a function of depth.
• The more commonly used retinal OCT uses 820-nm light, which allows for excellent tissue penetration to the level of the retina.• The anterior segment OCT utilizes 1310- nm light, which has greater absorption resulting in limited penetration.
• This allows for increased intensity of the light as decreased amounts reach the retina.• The light is 20 times more intense, giving a much greater signal-to-noise ratio.• This increased intensity allows for increasing the speed in imaging 20 times, with decreased motion artifact.
• Compared with other imaging modalities, OCT has a higher-depth resolution.• Resolution is determined by the wavelength and the spectral bandwidth of the light source, Shorter wavelengths and wider bandwidths provide better resolution.
Types of oct system There are two principles of image acquisition and data processing in anterior segment OCT:• Time domain and• Fourier domain algorithms.
• In time domain OCT, there is a mechanical moving part that performs the A-scan, Thus, the rate of the scan is limited by the movement of the part.• In Fourier domain OCT, the information in an entire A-scan is acquired by a charge-coupled device (CCD) camera simultaneously. As there is no mechanical movement, the scan time in Fourier domain OCT is faster. This is an important advancement because faster acquisition time means lesser variability in the result due to the patient’s eye movements.
Scans• Anterior Segment Scan (16 x 6 mm)• Single, Dual or Quad lines• 256 A scans / .125 sec acquisition per line• High Resolution Scan (10 x 3 mm)• Single or Quad• 512 A-scans / .25 sec acquisition per line• Pachymetry Scan (10 x 3 mm)• 8 radial lines• 128 A scans / 0.5 sec total acquisition time• All Scans adjustable in orientation and direction
PHAKIC IOL PRE OP PLANNING POST OP OBSERVATIONACD PCIOL DEPTH AND CENTRATIONANGLE TO ANGLE IRIS POSITIONANTERIOR CHAMBER ANGLE CRYSTALLINE LENS VAULTIRIS OR CRYSTALLINE LENS ENDOTHELIAL SAFETY DISTANCEPOSITIONACCOMADITVE ANALYSIS ACCOMADITIVE ANALYSIS
Advantages of AS OCT• Technicians can do the scanning• Imaging flexibility• Faster imaging reduces error• Image through an opaque cornea• Its easy to image accommodative changes• Scans can be taken immediately after surgery
Limitations• Pigmentation on the posterior side of the iris blocks the penetration of infrared light.• Trabecular meshwork/ ciliary body not seen• Manual angle measurement
History• History of present illness• Associated history• Past history• Family history
History• History of present illness :age of onset• Associated history duration• Past history one/both eye• Family history variability
History• History of present illness• Associated history : diplopia• Past history odynophagia• Family history muscle weakness cardiac problem night blindness
History• History of present illness• Associated history• Past history : trauma/ surgery• Family history contact lens lid edema allergy dry eyes
History• History of present illness• Associated history• Past history• Family history
evaluation of ptosis• head posture,Eyebrow position, eyelid masses, inflammation, proptosis• pupillary size, reaction, heterochromia• Best corrected Visual Acuity: In infants, make sure infant can fix and follow light with each eye• Cycloplegic Refraction
In children• Presence or absence of Lid fold• Head tilt• Iliff test
Measurements• Vertical fissure height• Margin reflex distance• LPS action• Lid crease level• Lid level on down gaze
Vertical fissure height• The distance between the upper and lower eyelid in vertical alignment with the center of the pupil in primary gaze, with the patient’s brow relaxed.• Normal – 9-10mm in primary gaze• Should be seen in up gaze, down gaze and primary gaze• Amount of ptosis = difference in palpebral apertures in unilateral ptosis or Difference from normal in bilateral ptosis
Grading of severity of ptosis < or = 2mm : mild ptosis = 3 mm : moderate ptosis = or > 4 mm : severe ptosis
MRD• Margin-to-reflex distance 1 (MRD1) : is the distance from the central pupillary light reflex to the upper eyelid margin with the eye in primary gaze.• A measurement of 4 - 5 mm is considered normal.• If the margin is above the light reflex the MRD 1 is a +ve value.• If the lid margin is below the corneal reflex in cases of very severe ptosis the MRD 1 would be a –ve value.
MRD• Margin-to-reflex distance 2 (MRD2) : is the distance from the central pupillary light reflex to the lower eyelid margin with the eye in primary gaze. . • The MRD1 plus the MRD2 should equal the palpebral fissure measurement
Levetor function• is the distance the eyelid travel from downgaze to upgaze while the frontalis muscle is held inactive at the brow.• The normal levator function is between 13- 17mm
• Lid excursion is a measure of the levator function. The frontalis action is blocked by keeping the thumb tightly over the upper brow and asking the patient to look up from down gaze and measuring the amount of upper lid excursion at the center of the lid.
Grading of levator action< 4mm – poor levator function5-7 mm – fair levator function8-12 mm – good levtor function
Lid crease• Position is the distance from the crease to lid margin• Normal – 8 to 10mm in primary gaze• An absent lid crease is often accompanied by poor levator function.• If a lid crease is present but is higher than normal and if a deeper upper lid sulcus is found on that side, note these as signs of a levator aponeurosis disinsertion.
Phenyl ephrine test• Patients with minimal ptosis (2 mm or less) should have a phenylephrine test performed in the involved eye or eyes• Either 2.5 or 10% phenylephrine is instilled in the affected eye or eyes. Usually two drops are placed and the patient is reexamined 5 minutes later. • The MRD1 is rechecked in the affected and unaffected eyes .• A rise in the MRDl of 1.5 mm or greater is considered a positive test. This indicates that Müllers muscle is viable