UBM and ASOCT provide high-resolution cross-sectional images of the anterior segment including the cornea, anterior chamber, angle, and iris. ASOCT uses optical coherence tomography with a wavelength of 1310nm for improved penetration and reduced retinal damage compared to posterior segment OCT. It allows high-speed imaging of dynamic structures. ASOCT has applications in assessing corneal diseases and procedures, glaucoma (including angle anatomy and iridotomy evaluation), and intraocular lens implantation. Measurements of angle width parameters help evaluate angle closure risk. While valuable for objective angle assessment, ASOCT cannot image all anatomical structures involved in glaucoma.

1. ROLE OF ASOCT & UBM
DR.M.DINESH

2. UBM (ultrasound biomicroscope), ASOCT (anterior segment
optical coherence tomography) provide detailed
• cross-sectional images of the
• cornea,
• anterior chamber,
• angle,
• iris, and
• in case of UBM the lens.

3. • Optical coherence tomography (OCT) is a
• cross-sectional,
• 3D,
• high-resolution imaging modality that uses
• low coherence interferometry to achieve
• axial resolution in the range of 3–20 μm.
• Anterior segment imaging using OCT was first demonstrated in 1994 by
Izatt, et al. using light with a wavelength of 830 nm

4. principle of OCT
1. The principle of OCT is based on Michelson’s interferometry
2. Posterior segment OCT uses a lower wavelength of light at 830 nm
3. ASOCT uses a higher wavelength 1310 nm

5. The anterior segment OCT (ASOCT) at 1310 nm wavelength of light is
better suited for AC angle imaging due
1. Reduced scattering
1. ensures better penetration through ocular structures like the
sclera and the iris and hence a more detailed AC angle
morphology
2. More dissipation/absorption
1. The higher(1310 nm) wavelength light is strongly absorbed by
water in ocular media(vitreous) and therefore, only 10% of the
light incident on the cornea reaches the retina causing no damage
to the retina
2. The improved retinal protection allows for the use of high power
illumination which enables highspeed imaging

6. The high-speed imaging helps in various ways:
1. Reduces examination time
2. Eliminates motion artifacts
3. Enables imaging of dynamic ocular events
4. Allows for rapid survey of relatively large areas.

7. The ASOCT has 6 imaging modes:
1. High-resolution cornea single
2. High-resolution cornea quad
3. Pachymetry
4. Anterior segment single
5. Anterior segment double
6. Anterior segment quad

8. single mode, only a single image will be
obtained at the desired angle.

9. 1. Double mode takes images at the
preset angles of 20 to 200, &160 to
340
2. 1800 preset angle separation will
remain the same i.e.,when manually
changing the angle of image
capture, all angles will rotate
together

10. 1. quad mode of both high-
resolution cornea and AS
2. 4 cross-sectional images are taken
at 0 to 180, 45 to 225, 90 to 270,
and 135 to 315 degrees,
respectively
3. If the operator adjusts the angle by
15 degrees, the new images will be
captured at 15 to 195, 60 to 240,
105 to 285, and 150 to 330.
4. All images have been rotated by
15 degrees and are still separated
by
90 degrees.

11. Two resolution modes of imaging
Standard resolution imaging High/enhanced resolution
imaging
Broader view of AS
16 mm width /6 mm depth
More detailed imaging
10 mm width/3 mm depth
Full overview of AS:
Cornea, anterior chamber, iris
and both angles
Cornea and any segment
needing detailed evaluation
256 scans 0.125 seconds 512 scans 0.250 seconds

12. Measurement tools
The different tools available are:
1. Calipers
2. Flap tool
3. Angle tools—ICAT (Iridocorneal angle tool) and ACA (Anterior
chamber angle) tools
4. Chamber tools for anterior chamber depth and width
measurements
5. Anterior segment refractive tool set.

13. (A) The caliper tool;
(B) The flap tool;

14. (C) The iridocorneal angle tool;
(D) The chamber tools:
1. Central corneal thickness;
2. Anterior chamber depth;
3. Angle to angle distance; and
4. Crystalline lens rise

16. Applications of ASOCT
can be broadly grouped into applications in:
• Cornea
• Biometry and phakic IOL
• Glaucoma
Limitations
ASOCT
a. Cannot penetrate through pigmented tissue
b. Cannot image anything past the posterior pigmented epithelium of
the iris.

17. Applications in Cornea
1. LASIK
2. DSAEK
3. Dystrophies and degenerations
4. Corneal inflammatory and infltrative disorders
5. Keratoplasty
6. Keratoconus
7. Intacs
8. Descemets detachment

18. 1. ASOCT can assist in diagnosis and documentation of corneal
conditions such as dystrophies and degenerations, as well as
assorted inflammatory pathologies.
2. It can be used to diagnose and manage corneal infiltrates, ulcers,
dellen or scars.
3. The depth and extent as obtained by ASOCT is superior to that of
anterior segment photography.
4. Monitoring of corneal infection is possible especially when deep,
and aggressive infection occurs.
5. Hypopyon and hyphema can also be monitored as a result of
severe infection or trauma.
6. ASOCT has the capability to determine the depth of a foreign
body or
the presence of residue once removed

19. 7. Corneal dystrophies affect one or more layers of the cornea.
8. High definition images obtained by ASOCT allow the practitioner to
visualize the epithelium, stroma and endothelium with clear
differentiation.
9. ASOCT can document corneal topography pre and post Descemet’s
stripping automated endothelial keratoplasty (DSAEK) in the
treatment of pseudophakic bullous keratopathy (PBK)
10. ASOCT has the capability to image keratoconus and other ectastias
to determine and document the severity of thinning and scarring.
11. ASOCT pachymetry maps scan areas from the central cornea to 10
mm, calculating a global thickness measurement in both clear and
opacified corneas.
12. Pachymetry maps allow the surgeon to create accurate and
repeatable flap thicknesses in LASIK surgical
planning.Postoperatively, residual bed thickness can be imaged
utilizing these thickness maps

20. Biometry in Postrefractive Surgery Cases
1. To measure the posterior corneal curvature accurately,
2. To develop an IOL power formula based on the ASOCT corneal
power measurement.
Phakic Intraocular Lens
1. The ASOCT is looked upon with a great deal of optimism regarding
its
potential to guide the sizing of IOLs

21. Some of the Phakic IOL tools. It shows the “RAINBOW”
(0.5 mm, 1 mm and 1.5 mm from the cornea), “SAFETY” (distance from
cornea) at 180°, center and 0° and “VAULT” (distance between Phakic
IOL and crystalline lens) at 180°, center and 0°)

22. The use of the “flap tool” in post-LASIK cases to measure the precise
thickness;

23. (B) The global pachymetry map, which is formed from 16 modifed high
sresolution scans

24. Applications in Glaucoma
ASOCT is used:
• to study the normal anatomy and physiology
• for screening of the spectrum of angle-closure glaucoma
• to study plateau iris syndrome
• to study mechanism of malignant glaucoma
• to test the efficacy of laser peripheral iridotomy, and
• to test the patency of glaucoma drainage device.

25. ASOCT of the angle Gonioscopy
It is a non-technical device It requires technical skill
Objective test Subjective test
Comfortable procedure May be discomfortable
Non-contact procedure Contact procedure
No light artifact
Light , indentation, and
accommodation
artifacts may be found
Control for focus is easy More difcult procedure technically
Able to document landmark Documentation is difficult
It is not a standardized
procedure
Standardized procedure. Different
grading systems and lenses are
required
expensive inexpensive

26. Two photographs of the same angle
A.The photo on the left was taken with the room lights on and it shows a
clearly open angle.
B.The one on the right was taken after turning the lights off, which
demonstrates iris-cornea apposition anterior to the scleral spur which is
marked by the arrow
i.e.,oppositional angle closure
1.Angle-closure

27. case of synechiae angle closure
subtle case of synechial
closure in an eye with a
plateau iris

28. Laser Iridotomy
ASOCT images of an eye: (A) Before and; (B) After undergoing laser
iridotomy
The angle appears occludable before procedure, but it clearly
demonstrates that the iridotomy has increased the angle’s width

29. (A) The angle appears occludable before procedure; (B) The iridotomy
has increased the angle’s width

30. • Iridotomy procedures have shown dramatic improvement of the
angle
structure when pupillary block mechanisms are present.
• Certain patients’ angles do not improve as expected following
iridotomy, nonpupillary block mechanisms (i.e., plateau iris, lens-
related anterior rotation of the iris) can be easily identified.
• A limitation of the ASOCT during angle imaging
• inability to visualize pathology causing primary or secondary
glaucoma including trabecular pigment or narrow bands of
peripheral synechiae.

31. Defnitions
Angle Opening Distance
Angle opening distance (AOD500) is calculated as the perpendicular
distance measured from the TM at 500 µm anterior to the scleral spur
to the anterior iris surface.
AOD 750 is calculated as the perpendicular distance measured from the
TM at 750 µm anterior to the scleral spur to the anterior iris surface.

32. Angle Recess Area
ARA is measured as described by Ishikawa, et al.
1. The defining boundaries of this triangular area are the AOD 500 or
AOD 750 (the base), the angle recess (the apex), and the iris surface
and inner corneoscleral wall form sides of the triangle
2. The ARA is a better measurement parameter than the AOD because it
takes into account the whole contour of the iris surface rather than
measuring at a single point on the iris as is the case with the AOD.
3. ARA may be less sensitive in identifying a narrow angle in eyes with a
relatively deep angle recess.

33. B) Angle recess area

34. Trabecular Iris Space Area (TISA):
The defining boundaries of TISA a trapezoidal are as follows:
1. Anteriorly -the AOD 500 or AOD 750;
2. Posteriorly -a line drawn from the scleral spur perpendicular to the
plane of the inner scleral wall to the opposing iris;
3. Superiorly -the inner corneoscleral wall;
4. inferiorly -the iris surface
5. this parameter represents the actual
filtering area more accurately when
compared with the ARA because the
TISA excludes the nonfiltering region
behind the scleral spur.

35. Trabecular iris contact length (TICL)
defined as the linear distance of iris contact with the corneoscleral
surface beginning at the scleral spur and extending anteriorly in an
anatomically
apposed or synechially closed-angle.

36. Trabecular iris angle
defined as an angle measured with the apex in the iris recess and the
arms of the angle passing through a point on the TM 500 µm from
the scleral spur and a point on the iris perpendicularly

37. The composite image of all the parameters AOD, ARA and
TISA

38. Scleral Spur Angle
defined as an angle measured with the apex at the sclera spur and the
arms of the angle passing through a point on the TM 500 µm from the
scleral spur
and a point on the iris perpendicular.

39. Plateau Iris :
Plateau iris configuration (PIC)
1. is characterized by an appositional angle with a flat iris configuration, in
contrast to an anterior bowing of the iris seen in a “typical” angle
closure glaucoma in which there is a more crowded anterior chamber
due to a hyperopic/short eye.
2. Classically with PIC
1. the iris configuration is planar and the depth of the AC is N
2. the iris root is often short and inserted anteriorly on the ciliary face,
causing a shallow and narrow angle.
3. With plateau iris configuration there is a relative pupil block
mechanism.

40. A)figurative images of a normal eye
B)eye with plateau iris syndrome

41. ASOCT image of an eye with plateau iris

42. Plateau iris syndrome (PIS)
1. d/to an abnormal anterior position of the ciliary body which
alters the position of the peripheral iris in relation to the
trabecular meshwork resulting in obstruction to aqueous
outflow.
2. PIS may be triggered by spontaneous pupillary dilation (for
example, in darkness), or in response to mydriatic agents.
3. Slit lamp evaluation of patients with plateau iris configuration
usually shows a normal ACD(ant chamb depth) and a flat iris
plane.
4. on indentation gonioscopy a “double hump sign” is chr of PIS .
1. peripheral “hump” - ciliary body propping up the iris root
2. central “hump” - the central third of the iris resting over the
surface of the lens

43. 5. Though, plateau iris is believed to have a deep central chamber
unlike a typical narrow angled individual who is hyperopic, UBM
studies have found patients with plateau iris to have shallower
anterior chamber.

44. Malignant glaucoma :
1. following filtration surgery it remains one of the most challenging
problems.
2. It refers to a shallow or flat central and peripheral anterior chamber
caused by the forward movement of the lens-iris and iris-hyaloid
diaphragm accompanied by elevated IOP, in the presence of a patent
peripheral iridectomy.
3. ASOCT findings include
1. irido-corneal touch,
2. anterior displacement of the iris root, and
3. appositional angle-closure.

45. 4. The imaging of anterior rotation of the ciliary body with apposition to
the iris is found with UBM but not with ASOCT because of absorption
of infrared light by deeper scleral tissues and the pigment epithelium
of the iris & thereby the visualization of lens, ciliary body, or anterior
vitreous structures was limited .
5. However, the UBM method requires a coupling medium in an
immersion bath, which restricts examinations in the immediate
postoperative period.

46. 5. The goal of the treatment for malignant glaucoma has been directed to
restore
the normal aqueous flow into the anterior chamber with resultant
deepening. ASOCT has revealed to be helpful for the objective
assessment of the therapeutic effects, and to recognize eyes that are
unresponsive to medical or surgical management with a recurrent flat
anterior chamber postoperatively
6. An important risk factor to develop malignant glaucoma is a chronic
glaucoma with a narrow irido-corneal angle and an increased scleral
thickness, which is recognised by ASOCT in the early stagesof a
ciliolenticular block monitoring central and peripheral shallowing of the
anterior chamber to improve therapeutic management and prevent
progression

47. Postoperative flat chamber: malignant
glaucoma

48. Bleb morphology
1. it is an indicator of bleb function and a predictor of bleb-related
complications such as bleb leak, blebitis, and bleb-related
endophthalmitis.
2. Bleb morphology indicates the function of the filtration shunt created
by the trabeculectomy procedure and guides the ophthalmologist in
performing interventions such as needling and suture lysis in order to
optimize shunt function.
3. ASOCT has been used to image trabeculectomy bleb to provide
information about internal structure that is not available at the slit lamp.
4. It is able to provide clear images of the blebwall, cavity, flap and ostium
as displayed below.
5. Successful blebs display conjunctival thickening as a hallmark of
success,
regardless of degree of bleb elevation. This reflects facility of
transconjunctival aqueous flow.

49. 5. Highly elevated blebs sometimes display marked conjunctival
thickening and only a small cavity.
6. In failed blebs, ASOCT is particularly useful in imaging failed blebs to
demonstrate the level of failure.
7. Ostial closure, flap fibrosis and presumed episcleral fibrosis in the
absence of the former two situations are all clearly demonstrated.
8. In the early postoperative period, a failing bleb with a closely apposed
scleral flap may be resuscitated by suture lysis, resulting in a more
expanded bleb.
Hence ASOCT is a useful tool to image trabeculectomy
blebs and may aid the clinician in postoperative bleb management.
9. It can also image the intrascleral lake and implant used in non-
penetrating glaucoma surgery (deep sclerectomy) and glaucoma
drainage devices

50. Trabeculectomy bleb

51. Ultrasound biomicroscopy (UBM)
is a method of high frequency ultrasound imaging used to generate
images approaching light microscopic resolution up to a depth of 4–5
mm from the surface.
instruments
3 main components of the system are
1. the transducer
2. Signal processor and
3. an articulated arm to steady the scanning head and provide precise
motion control
The system is controlled and synchronized by a computer for further
analysis
instruments frequencies between 35 and 100 MHz,
resolution of 60 microns and a depth penetration up to about 4 mm.

52. The UBM machine from Zeiss-Humphrey with a 50 MHz probe

53. The technique of performing UBM with the probe immersed
in a coupling solution placed over the area of interest.

55. The technique :
1. Technique used for examination is the immersion technique using a fluid
standoff
2. An eye cup permits evaluation avoiding distortion caused by the eyelids
and permits the use of a coupling solution.
3. The procedure is done in the supine position under topical anesthesia
4. The eyecup is used to separate the lids and is filled with 1%
methylcellulose or normal saline.
5. The transducer is immersed in the solution and placed directly over the
part to be scanned.
6. As the arm can be tilted as well as rotated in the horizontal plane, various
sections of the same area can be scanned.
7. The cornea and anterior segment can be easily studied, and the
conjunctiva, sclera and peripheral retina up to the limits of rotation of the
eye in various directions.

56. Ultrasound Biomicroscopy of Normal Ocular Structures
1. The cornea is seen as a multilayered structure, with a highly
reflective epithelium, a high reflective Bowman’s membrane, and a
high reflective line consisting of the endothelium and Descemet’s
membrane.
2. UBM can measure
1. ACD
2. anterior chamber angle
3. Iris thickness
4. iridolenticular contact distance.
3. The ciliary body, ciliary processes and the ciliary sulcus are well
distinguished on UBM. The ciliary processes show a
variable configuration. The anterior lens surface can be seen, as
well as the anterior zonules. The posterior zonule and vitreous
face may be seen in very shallow chambered eyes.

57. Uses of UBM :
Corneal and Scleral Diseases
1. The UBM performed in opaque corneas can be helpful in deciding the
prognosis and planning surgery in eyes undergoing keratoplasty.
2. “Virtual gonioscopy” in these instances gives an idea of angle details.
The lens status can also be assessed.
3. Depth of involvement in scleral and episcleral inflammation can help in
diagnosis and evaluating response to treatment.
4. In cases of necrotizing scleritis there may be a spontaneous bleb
formation and the communication can be picked up on the UBM.

59. Ocular Surface Tumors :
1. Conjunctival and corneal surface tumors can be assessed
2. Information regarding the depth of tumor ,involvement of adjacent
and intraocular structures and tumor residue/recurrence following
surgical excision
The UBM image of the same eye shows , mass
is
homogenous, low reflective, conjunctival and
does not involve the sclera
Image showing a nasal limbal mass

60. Glaucoma :
1. UBM can image all the angle components, iris, and ciliary body
complex.
2. It is also possible to study the behavior of the iris and angle under
various conditions of illumination
3. Angle-closure can occur at four anatomic levels;
1. the iris (pupillary block),
2. the ciliary body (plateau iris),
3. the lens (phacomorphic glaucoma, and
4. The anterior vitreous face (malignant glaucoma).

61. Narrow angle with plateau iris Opening up of the angle following a laser
iridotomy

62. Poor response to peripheral iridotomy may be due to the plateau iris
configuration, where the anteriorly located ciliary processes block the
ciliary sulcus preventing the peripheral iris from falling back after iridotomy

63. Malignant glaucoma :
1. UBM - able to demonstrate anterior rotation of the ciliary processes to
make a diagnosis of malignant glaucoma
2. It has allowed classification of malignant glaucoma into two groups;
one with supraciliary effusion, which responds to medical management
better and another without effusion that usually requires surgical
management.
3. UBM helps in deciding the course of management at an early stage
1. Extremely shallow anterior chamber.
2. Occluded angle.
3. Forward rotation of the ciliary body.

64. In pigment dispersion syndrome there is reverse pupillary block where the
posterior bowing of the iris causes an increase in iris-lens contact and
sometimes iris zonular contact as well.
Widely opened angle
Typical Posterior bowing of the peripheral iris

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

66. 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

67. Cataract surgery :
1. Preoperative phacodonesis
2. Area of zonular loss
3. the integrity of the posterior capsule especially in cases of
traumatic cataract can be assessed & plan surgery accordingly.

68. IOL Complications
1. The UBM is useful in studying various IOL complications.
2. Optic and haptic locations can be assessed accurately by looking for
a strong echo at their interface plane.
3. This ability to image the IOL helps in determining whether structural
changes induced by the IOL are responsible for postoperative
complications.
4. These can be due to retained cortex or contact of the IOL haptic
with the iris or ciliary body.
5. Poor quality of vision due to tilt or decentration of the IOL may
necessitate repositioning or exchange.
6. Demonstration of malpositioned haptics, zonular and capsular
dehiscence, haptic erosion into ocular tissues, decentration and tilt
of IOL can be helpful in assessing these IOL related complications
and planning management strategies

69. Anterior Segment Cystic Lesions and Tumors
1. Cystic lesions of the cornea, iris and ciliary body
Iris tumors and nevi
Small ciliary bodytumors as well
as cysts, which can mimic tumors are best assessed on UBM
2. The UBM is useful in defining the posterior extent of ciliary body
tumors as well as the anterior extent of peripheral choroidal
tumors

70. Trauma :
UBM can demonstrate anterior segment foreign bodies, cyclodialysis
clefts, zonular damage and angle recession

71. 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.

72. 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.
Zonular rupture

73. Vitreoretinal Surgery
1. UBM clearly images structural changes at the sclerotomies in
post pars plana vitrectomy (PPV) & it distinguishes healing
patterns
2. UBM is helpful in evaluating PPV related complications such as
anterior hyaloidal fibrovascular proliferation and retinal break
formation and planning management.

74. Anterior segment Inflammation and Hypotony
1. Uveitic eyes very often have miotic pupils and hazy media making it
difficult to evaluate the posterior segment.
2. Conventional ultrasound is able to image the posterior segment but
the UBM helps in studying the ciliary body and pars plana in detail,
identifying edema, thickening, atrophy of ciliary processes, cyclitic
membranes, pars plana exudates and membranes as well as ciliary
body traction
3. In cases of unexplained hypotony, supraciliary effusion, ciliary body
membranes, causing traction or atrophic ciliary processes can be
demonstrated

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

76. THAN Q
Ref :
Diagnostic Procedures in OPHTHALMOLOGY 3rd ed HV Nema

78. Uses of ASOCT in LASIK cases:
1. Comprehensive pachymetry map of the entire cornea can be derived
2. The thickness of the cornea from the individual scans as well as the
global pachymetry map can be used to determine ablation rates
3. One of the major factors causing variation in this parameter is
stromal hydration.The ASOCT can measure this hydration minimizing
the differences between planned and actual ablation depths
4. Superior resolution of morphological features
5. Detection of normal from abnormally thin corneas in which
subtractive refractive surgery like LASIK may need to be avoided

79. 6. ASOCT has been utilized in monitoring the epithelial healing progression
under therapeutic contact lenses (TCL) following lamellar keratoplasty
and epiLASIK.
7. Visualizing the epithelium postoperatively allows the surgeon to remove
the TCL at the appropriate time without traumatizing the new epithelium
or risking a secondary infection by leaving the TCL longer than necessary.

80. Schematic diagram showing the processes involved in
obtaining scans using the UBM

81. Optical Principles
• Imaging with OCT is based on Michelson interferometer and
includes complex analysis of reflections of low coherence light from
the ocular tissue (low coherence interferometry).
Michelson Interferometer
• A beam of light passes through a semi-transparent mirror that
splits the beam into two.
• These two beams of light are then thrown on two equidistant
mirrors;
reflected light from these mirrors is then picked up and summed up
by a detector.
• The equidistant mirrors reflect the light wave in same phase

82. • If one of the mirrors is moved by a distance less than the
wavelength of the incident light, the reflected lights from the two
mirrors will then possess a phase difference.
• This phase difference then produces an interference pattern at
the level of the detector