This document compares and contrasts AS-OCT (anterior segment optical coherence tomography) and ultrasound biomicroscopy (UBM) imaging techniques for evaluating the anterior eye segment. It discusses that AS-OCT provides non-contact, high resolution cross-sectional imaging of the anterior segment structures without touching the eye. UBM uses high frequency ultrasound to generate detailed 2D images of the anterior segment, allowing visualization of structures like the iris and angle. While both techniques allow qualitative and quantitative assessment of the anterior chamber angle and structures, AS-OCT has advantages of being non-contact, faster imaging, and less operator dependency compared to UBM. However, UBM can image deeper into the posterior iris and has greater penetration than

1. AS-OCT AND ULTRASOUND
BIOMICROSCOPY
Dr Shylesh B Dabke
Glaucoma Fellow
Aravind Eye hospital
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2. Overview
• Because anatomy plays a large role in chronic angle closure,
evaluating the angle anatomy is a critical first step in treating
this disease.
• Using a combination of various AS imaging technique examiner
wil get a clear picture of the angle anatomy and help to make
appropriate treatment decisions.

3. • Gonioscopy is the current gold standard, but imaging
techniques such as Ultrasound biomicroscopy (UBM),
Scheimpflug photography, and anterior segment optical
coherence tomography (AS-OCT) provide additional valuable
information.

4. Gonioscopy
• Gonioscopy provides the examiner with a
dynamic, broad view of the angle.
• Has ability to analyze the angle with/without
compression (PAS vs appositional angle
closure.
• Although quick, inexpensive, and valuable, it is
also subjective and difficult to perform.
• Reproduciability, quantitative information
cannot be obtained.
• Therefore less than ideal for research and in
clinical situations where repeated
measurements are needed.

5. SCHEIMPFLUG IMAGING
• This technique uses light scattering to image
the anterior chamber.
• Although the resolution of the images is high
this method is of limited usefulness for
evaluating the angle because of its inability to
image the peripheral angle in many eyes.

6. AS-OCT
UBM

7. ANTERIOR SEGMENT -
OCT

8. • First described using the same wavelength of light as retinal
OCT, namely 830nm.
• OCT imaging of the anterior segment with a longer
wavelength of 1310nm was developed later on and had the
advantages of better penetration through sclera
• Rapid, non contact method that maybe performed by a
technician with patient sitting Upright.

9. • Obtains a high-resolution cross-section of the anterior segment
without touching the eye.
• Enables visualisation of the form, site & position of AC
components.
• Defines & measures the distances between them.
• Machine automatically eliminates distortion induced by optical
transmission factors.

10. • Reflex Saturation Beam indicates perpendicularity of the eye
to the scanning beam and minimal tilting of the image.
• The scan dimensions are 16 x 6 mm and 4 image frames are
averaged.
• Resolution is 2-20microns which makes it suitable for
measurement of finer eye structures.

11. • Qualitative assessment
- An important landmark to identify in ASOCT images is the
scleral spur.
- This is visible as an inward projection of the sclera at the
junction between the inner scleral and corneal curvatures.
- Apposition between the iris & inner corneo-scleral wall has
been used as a qualitative method of detecting angle closure

12. • Quantitative Assessment
- Quantitative measurement of the AC angle is possible with
in-built software & requires identification of the scleral spur.
- The commonly used quantitative parameters
* Angle opening distance(AOD500/AOD750)
*Angle recess area(ARA500/ARA750)
*Trabecular space area(TISA500/TISA750)

13. Angle opening distance (in mm): Perpendicular distance between a point 500µm (AOD
500) or 750 µm (AOD750) anterior to the scleral spur and the opposing iris.
Angle recess area (in mm2): The triangular area (ARA 500 or 750) bounded by the AOD
500 or 750, the anterior iris surface and the inner corneo-scleral wall
Trabecular Iris space area (in mm2): Trapezoidal area (TISA 500 or 750) bounded by
the AOD 500 or 750, the anterior iris surface, the inner corneo-scleral wall and the
perpendicular distance between the scleral spur and the opposing iris.

16. • SL – OCT(Heidelberg Engineering)
Visante (Carl Zeiss Meditec, Inc.)
• The Visante OCT (Carl Zeiss Meditec) is a time-domain OCT
device that scans the anterior segment, generating images that
extend from limbus to limbus.
• Newer Fourier-domain OCT (FD-OCT) intended for posterior
segment imaging are increasingly evolving to include anterior
segment imaging.
• FD-OCT units have shorter wavelengths (typically 800-840 nm)

17. Newer Modalities
• A new swept source FD-OCT device (Casia SS-1000; Tomey
Corporation) can rapidly obtain high-resolution scans with
3D reconstruction of the anterior segment.

18. Clinical use in glaucoma
• An adjunct to gonioscopy as well as a substitute when
gonioscopy is not feasible.
• Useful as a patient education tool, especially when laser
peripheral iridotomy is being recommended.
• Phototherapeutic keratectomy to assess the depth of corneal
opacity.
• LASIK for CCT & to measure flap thickness.
• Keratoconus & INTACS for CCT & positioning of INTACS.
• Cysts of anterior segment to diagnose etiology.
• Biometry for phakic IOL.

19. AS-OCT & Glaucoma
• Useful tool for evaluating filtering bleb or GDD in post-op
period.
• Clinical description of bleb is subjective & there may be cases in
which clinical appearance does not correlate with bleb
function.
• Visualising intra-bleb morphology with AS-OCT may enhance
our understanding of different surgical outcomes.

20. AS-OCT over Gonioscopy
• Two common flaws in the performance of clinical gonioscopy
include the placement of pressure on the cornea and the use of
excessive amounts of light.
• Both typically produce the illusion of an open angle in a
patient who otherwise may have narrow or even appositionally
closed angles.
• AS-OCT provides little light artifact. It can actually dynamically
show how an angle imaged in bright light may appear open but
look narrow when assessed in the dark.

21. Newer Uses for AS-OCT
• Measuring the tear film
Although this work is still mostly showing value in research
situations
• Measuring contact lens fit

22. Advantages
• Non contact.
• More physiological.
• Shorter imaging time.
• Less learning curve for operator.
• Target may be used to induce accommodation in eye
imaged.
• Less inter operator variability.
Limitations
• No penetration of pigmented iris epithelium.

29. Failed flat bleb.Trabeculectomy site seen but no subconjunctival bleb
High elevated tense encapsulated bleb
Same patient with scanned section of bleb only

31. Penetrating keratoplasty

32. Intacs

33. Descement’s Detachment

35. Granular Dystrophy

36. Ultrasound Biomicroscopy(UBM)
• High frequency
ultrasound technology.
• Detailed 2D gray scale
image of ant segment.
• Probe Frequency – 20, 35
and 50MHz.

37. Principle
• It acts on a principle similar to that of the B-scan (10Mhz)
• Frequency 50Mhz
• More frequency, less penetration(5mm) and more resolution
• Limited depth of penetration is also associated with a
smaller angular field (4x4 mm)

38. Patient in supine position
Local anesthetic
Eye cup (plastic or silicone) which is used
to create a small water bath
The crystal of the transducer is placed in
saline approximately 2 mm from the eye
surface.
Methyl cellulose or normal saline can
be used as coupling solution

41. Qualitative and Quantitative
Examination
• Structures
- Conjunctive, cornea, Ant Sclera
- Ant. Chamber angle structures
- Ciliary Body
- Ant. layers of lens, zonules & IOL
- Pars plana
• UBM pro 200 software in the machine automatically
measures all angle parameters by marking the scleral spur.

42. Quantitative parameters of UBM

43. Qualitative Ultrasound Biomicroscopy
• Glaucoma
• Cornea
• Tumors
• Trauma
• sclera
• Intraocular lenses
• Ocular adnexa

44. GLAUCOMA
Determine the mechanism of elevated intraocular
pressure (angle-closure versus open-angle) by showing
the relationship between the peripheral iris and
trabecular meshwork.
Open-angle Glaucoma
• Measure the anterior chamber
angle in degrees
• Assess the configuration of the
peripheral iris
• Evaluate the iris insertion in relation
to the trabecular meshwork
• See if there is an anterior insertion
of the iris or an anteriorly displaced
ciliary body
Narrow angles
• UBM shows the extent of angle closure
• Depth of the anterior and posterior
chambers
• Identifies pathologic processes pushing
the lens and iris forward.

45. PUPIL BLOCK GLAUCOMA
(A) The angle shows appositional closure owing to anterior bowing of the iris.
(B) The angle is open with a flattened iris after laser peripheral iridotomy.

46. To Determine Occludability of the Angle
• Perform dark room provocative testing with the UBM, to
study the spontaneous occlusion of the angle under
conditions of decreased illumination.
• Better than dark room gonioscopy because the latter is time
consuming and standardization of slit-lamp illumination is
difficult

47. PIGMENT DISPERSION SYNDROME
Classical picture
• Widely opened angle
• Typical Posterior bowing of the peripheral iris

48. Peripheral Anterior Synechiae
• Reveal the extent of irido corneal adhesions, even if the
cornea is hazy or opaque

49. Malignant Glaucoma
• Extremely shallow anterior chamber.
• Occluded angle.
• Forward rotation of the ciliary body.

50. Functional Status of Filtering Surgery
• Whether the sclerostomy aperture is patent or blocked
internally.
• whether the peripheral iridectomy is patent.
• whether the filtering bleb is flat, shallow or deep.

51. Cornea

52. Graft host junction
Epithelial bullae in oedema

53. Corneal Dystrophy
Lamellar keratoplasty Stromal scarring

54. Granular Dystrophy

55. TUMOURS
• Iris tumors, ciliary body tumors and anterior choroidal tumors
can be imaged.
• Borders of the tumor are usually detectable by the change in
reflectivity from surrounding structures.

57. The most common clinical presentation of an irido-ciliary
cyst is a peripheral iris elevation - the typical UBM finding
of a thin walled structure with no internal reflectivity is
diagnostic.

58. TRAUMA
CYCLODIALYSIS

59. Angle recession is imaged as a tear into the face of the
ciliary body. Ciliary body tissue is still imaged attached to
the scleral spur.

60. Zonular rupture

61. Hemorrhagic cyst within the iris

62. EPISCLERITIS

63. INTRAOCULAR LENSES
• Analysing IOL position
• AC depth after surgery can be measured with a high degree
of accuracy.
• Margins of the optic can be easily imaged & decentration
analysed.
• Haptic location in relationship to surrounding structures can
be determined.

67. Conjunctival and Adnexal Disease

68. AS-OCT VS UBM
• Optical VS Ultrasound
• Resolution : 15m VS 50m
• Scan Dimension : 16*6mm VS 5*5mm
• Image posterior iris : No vs Yes

69. Limitations
• Contact investigations - patient discomfort
• Supine position
• Cannot be used in
- Immediate Post op period
- Suspected open globe injury
- Younger children
• Time consuming
• Operator dependent