Aqueous humor AC Angle anatomy IOP measurement

1. GLAUCOMAMohamed Abdelzaher MD, FRCS

2. In all parts of the world glaucoma is
a major public health problem and
cause personal tragedy.
It is the second leading cause of
preventable blindness worldwide.

3. • The word glaucoma originally meant ‘clouded’ in Greek.
• glaucoma is defined as a disturbance of the structural or
functional integrity of the optic nerve that can usually be arrested or
diminished by adequate lowering of IOP.

4. • By Na/K ATPase pump,
Carbonic anhydrase in non
pigmented ciliary epithelium
• By Ultrafiltration & Diffusion

5. • 90% of aqueous outflow
• Sieve like structure at the AC
angle
• Formed of:
1. Uveal meshwork
2. Corneo-scleral meshwork
3. Juxta-Canalicular meshwork
Juxta-Canalicular meshwork is
the site of main resistance to
aqueous outflow

6. • Circumferential
canal in the
peri-timbal
sclera
• Drains into the
eli-scleral veins
via collector
channels

7. • 10% of aqueous outflow
• across the face of CB to the
supra-choroidal space
• some aqueous drains via the
iris

8. • Average IOP in general population (16 mmHg)
• Normal range (11-21 mmHg)
• IOP shows fluctuation with: (more in glaucomatous eyes)
1. Time of the day (higher in the morning 3-9 mmHg)
2. Respiration
3. Blood pressure
4. Heart beat
5. Season (higher in winter)
6. Body position (due to changes in CVP & subsequently epi-scleral pressure)
2 µl/min
7. Smoking, Caffeine (Increase IOP)
8. Marijuana (Decreases IOP)

9. • Some patients develop glaucomatous
damage with IOP < 21 mm Hg whilst others
remain unscathed with IOP well above this
level.
• A single IOP reading is mis-leading
• IOP should be measured 3 times at least at
different times of the day

11. For a dry, thin walled sphere, The
pressure (P) inside the sphere equals
the force (F) necessary to flatten its
surface divided by the area (A) of
flattening (i.e. P = F/A).
Imbert Fick Principle
‫للفهم‬

13. 3.06 mm
A pattern of two green
semicircular mires will
be seen, one above
and one below the
horizontal midline,
which represent the
fluorescein-stained
tear film touching the
upper and lower outer
halves of the prism.

14. • Calculations of IOP by GAT assume that central corneal
thickness is 545 μm.
• Thinner corneas under estimation
• Thicker corneas over estimation
For each 50 µm CCT change
IOP changes by 2-3 mmHg

15. • If > 3 D:
Measure IOP in 2 perpendicular meridians and
take the average OR
Rotate the prism so that the red line on the
tonometer housing is aligned with the
prescription of the minus axis

16. False low IOP False high IOP
Too little fluorescein Too much fluorescein
Corneal oedema
Tight collar, breath holding
(obstruct venous return)
Repeated measuring over short period
(massaging effect)
Pressure over the globe
e.g. examiner’s finger

17. measures the extent of corneal indentation
by a plunger of known weight
• Hand held (for bed bound,
anaesthetised)
• A Goldmann prism with portable light
source

18. • Hand held
• Contain transducer that measures the
applied force
• Can measure IOP in scarred or
oedematous cornea & through soft
contact lens
• Applanation tonometer
• Central cornea is flattened by jet of air
• Non contact
• Time required to sufficiently flatten the
cornea relates directly to IOP

19. • Measures IOP relatively independently of corneal
mechanical factors such as rigidity (Corneal
Hysteresis)

22. • The method for visualisation of AC angle using a
goniolens

23. • Using slit lamp, topical anaesthetic drops &
coupling fluid e.g. hydroxy propyl methyl
cellulose

24. • TM: Trabecular Meshwork
• SL: Schwalbe’s line
• SS: Scleral Spur
• CBB: Ciliary Body Band

25. Ciliary Body
Band
Scleral Spur
Trabecular
Meshwork
Schwalbe’s line
Grade 4 😃 😃 😃 😃 Widest
Grade 3 😃 😃 😃 Open
Grade 2 😃 😃
Grade 1 😃
Very
narrow
Grade 0 Closed

27. Indirect ophthalmoscope Direct ophthalmoscope
Slit lamp + Auxiliary lens
e.g. 90 D lens

28. orange-pink tissue
between the outer edge
of the cup and the optic
disc margin, composed
of retinal nerve fibres
exiting the globe
‘ISNT’ rule
Inferior rim is the
broadest
followed by Superior,
Nasal & Temporal
Cup/Disc ratio
(C/D ratio)
the diameter of the cup expressed as
a fraction of the diameter of the disc
Vertical C/D ratio
Asymmetry of 0.2 or more between
the eyes should also be regarded
with suspicion

29. • Caused by an irreversible decrease in the
number of nerve fibres, glial cells and blood
vessels

31. • Cup diameter is measured from the kink of
retinal vessels as they leave the ONH
• Asymmetry of cupping between both eyes
is diagnostic.

32. • Increased C/D ratio (Asymmetry between both eyes is diagnostic)
• Bayoneting (Z shape or double angulation of vessels at the edge of the disc)
• Laminar dot sign (appearance of lamina cribrosa pores)
• Disc haemorrhage
• Nasal shift of blood vessels
Z

33. • Zone Alpha (outer) black arrow
• Zone Beta (inner) white arrow

34. • RNFL defect precedes the development of
detectable ONH & visual field changes

36. • Course of the retinal ganglion cell axons within the
nerve fibre layer of the retina.
• (F, fovea; P, papillomacular bundle; T, temporal
raphe).

37. • Pseudo-colour map of ONH & peri-papillary
RNFL thickness.

38. An island hill of vision surrounded by an ocean of darkness

41. • Object in the Right half of the
visual field will stimulate:
Temporal retina of Left eye
Nasal retina of the Right eye
• Signals run through Left optic
tract toward the Left cerebral
hemisphere

42. Confrontation test

43. Perimetry is the subjective
measurement of the visual
field during central fixation
using either moving objects
(kinetic perimetry) or stationary
test stimuli (static perimetry)

45. F
Blind spot
15º temporal
to fixation
F

49. • Visual field defect (Island of darkness surrounded by sea of vision)
• Nothing can be seen at all within that area e.g. blind spot
• An area where objects of low luminance cannot be seen but larger or
brighter ones can.
• The patient is unaware of it e.g. blind spot
• The patient is aware of it (less common)

50. Most Field defects are Negative
scotomas, Which means that they will
not be perceived for instance as darker
or blurred areas. Instead the brain will
cause the so-called “Filling-in” creating
an inaccurate but ‘believable’ image in
the part the patient’s visual field is
defective.
A patient with with nasal field defect may
therefore fail to see the pedestrian &
the car shown in (A) but instead
perceive a believable image of the
intersection such as shown in (B).

51. • Up to 40% of optic nerve fibres might be damaged before
evident visual field changes appear. 🤔
•SWAP uses blue stimulus on yellow
background.
•It isolates short wavelength cones and
their connections; blue-yellow ganglion
cells.
•It is more sensitive to early glaucomatous
field changes than Standard Perimetry.