Glaucoma intro
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Glaucoma is the second leading cause of preventable blindness worldwide. It 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 intraocular pressure (IOP). IOP is produced by the continuous formation of aqueous humor in the eye and its outflow through two drainage pathways - the trabecular meshwork which accounts for approximately 90% of outflow, and uveoscleral outflow which accounts for the remaining 10%. Visual field testing is important for detecting glaucoma as up to 40% of optic nerve fibers may be damaged before visual field changes appear.
Glaucoma intro
- 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
- 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.