NEET PG-Optic Disc Changes in Open Angle Glaucoma-Ophthalmology

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Optic Disc :
→ Cup - allows blood vessels to enter & exit the eye; No specific function.
→ Neuro optic rim ( NRR) - contains neurons of optic nerve.
→ In glaucoma, Neuro Retinal Rim (NRR) surface area gradually decreases.
Cup Disc Ratio (CDR) : Formula: Cup Disc Ratio = Area of the cup/Area of the disc
→ Normal cup disc ratio = 0.3 (Range → 0.3 - 0.6)
→ Cup disc ratio (CDR) → ≥ 0.7 (Glaucoma)
→ Abnormal Cup disc ratio (CDR) indicates Neuro retinal rim damage.
Normal Optic Disc:
→ Clear margin
→ Colour of Neuro retinal rim (NRR) → Reddish pink colour
→ Optic disc (OD) → 0.3 - 0.6
Distribution of vessels:
→ 2 central retinal artery → Relatively narrow.
→ 2 central retinal vein → More dilated; PULSATES
→ 1 artery & 1 vein → Nasal
→ 1 artery & 1 vein →Temporal
→ If the central retinal artery pulsates, then:
1. IOP → very high (or)
2. BP → Very low - In emergency conditions
*Only pulsatile veins in the body*
→ Jugular Vein
→ Central retinal vein
Optic Disc Changes In Glaucoma:
↑ Cup disc ratio (CDR)
Disc pallor
Splinter Haemorrhage
Sign of nasalization
Laminar dot sign
Sign of Bayonetting
Doesn't follow ISNT rule
Glaucomatous optic Atrophy
Laminar Dot Sign:
→ Increase in the no of dots due to more exposed Lamina cribrosa.
→ Continued deepening of cup causes the exposure of underlying lamina cribrosa.
→ Recognised by grey fenestrae of lamina, seen on direct ophthalmoscope as grey dots
Sign Of Bayonetting:
→ Apparent discontinuity of blood vessels (Bayonetting sign: double angulation of blood vessels)
→ With complete loss of retinal tissue, retinal vessels may disappear as they make a sharp turn into the cup.
ISNT Rule :
→ ISNT → Inferior, Superior, Nasal, Temporal
Sequence of width decreases:
→ Inferior → Widest
→ Superior
→ Nasal
→Temporal → Narrowest
→ ISNT rule is broken in glaucoma - due to vertical ovalization of the cup.
Optic Disc Changes In Glaucoma:
→ ↑ Cup disc ratio (CDR)
→ Disc pallor
→ 1 artery & 1 vein → Nasal
→ 1 artery & 1 vein →Temporal

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