Download
1 / 60
730 likes | 1.83k Views
Glaucoma. Prithwiraj Maiti R.G.Kar Medical College. What is Glaucoma?. Glaucoma is a chronic, progressive optic neuropathy caused by a group of ocular conditions which ultimately lead to damage to the optic nerve and loss of visual function. Risk factor of Glaucoma.
E N D
Glaucoma Prithwiraj Maiti R.G.Kar Medical College
What is Glaucoma? • Glaucoma is a chronic, progressive optic neuropathy caused by a group of ocular conditions which ultimately lead to damage to the optic nerve and loss of visual function.
Risk factor of Glaucoma • The most common risk factor for development of glaucoma is a high intraocular pressure (IOP). • There may be 2 causes of rise in IOP: • Increased production of aqueous humour. • Decreased excretion of aqueous humour.
Pathways of Exit • The excretion of aqueous occurs through 2 different pathways: • Through the trabecular meshwork, situated in the angle of anterior chamber [Trabecular outflow] : Major pathway. • Through the ciliary body [Uveo-scleral outflow]: Minor pathway.
Site of Obstruction To Aqueous Flow • It is clear from the previous discussions that there may be obstruction to the aqueous flow in 2 positions: • Through the pupil. • Through the trabecular meshwork.
Pathogenesis of Glaucoma • Wherever the obstruction is, the final outcome is an increase in IOP, which has some bad consequences: a. The eye can withstand a high IOP for its protective coverings. But at the lamina cibrosa region, where the optic nerve enters into the eye, this can’t happen due to poor protective coverings.
b. The second mechanism of optic nerve damage is vascular compression.
Diagnosis of Glaucoma (dG) • The diagnosis of Glaucoma is made after looking for a combination of clinical signs: • A rise in IOP. • Changes in the optic nerve head. • Changes in the visual field.
dG: Rise in IOP • A diurnal variation in the IOP of > 6-8 mm Hg should always be investigated for Glaucoma even in the presence of a normal IOP (~20 mm Hg). • A single reading is useless, but periodic check up to detect baseline IOP and normal variation is important in diagnostic and curative purpose in Glaucoma.
dG: Change in Optic Nerve Head • The following changes are commonly seen in Glaucoma: • An enlargedCUP: DISC ratio (>0.5). • Assymetryin CUP: DISC ratio between 2 eyes (>0.2). • Thinning and pallor of neuroretinal rim. • Superficial disc hemorrhage. • Vascular signs (Baring of circumlinear vessels: BCLV). • Parapapillary atrophy.
In Glaucoma Normal
Baring of Circum Linear Vessels [BCLV] This vessel was originally at the rim but is now hanging out in space. It is a sign of GLAUCOMA and indication of Progressive cupping.
Parapapillary atrophy Parapapillary atrophy has been defined as atrophic abnormalities in the layers of the retinal pigment epithelium, photoreceptors and chorio-capillaris.
dG: Change In Visual Field: Scotoma Scotoma is an area of partial alteration in the field of vision consisting of a partially diminished/ entirely degenerated visual acuity that is surrounded by a field of normal/ relatively well-preserved vision.
Relative Paracentral Scotoma There are areas where smaller/ dimmer targets are not seen but larger/ brighter targets are seen.
Nasal step Appearance of a horizontal shelf in the nasal visual field.
Siedel Scotoma Start at poles of blind spot, arching over the macular area without reaching the horizontal meridian nasally.
Arcuate scotoma Start at superior pole, arching over macular area, never crossing horizontal meridian.
Double arcuate/ Ring Scotoma Only central and temporal vision are left.
Diagnosis of POAG • At least 2 of the 3 clinical signs should be present to diagnose POAG in the presence of a normal, open angle confirmed by gonioscopy: • An IOP> 21 mm Hg on >1 occasion and a diurnal variation of >8 mm Hg. • The presence of suggestive optic nerve head changes. • Visual field defects.
Diagnostic Techniques Used In Glaucoma • There are 2 important diagnostic tools for glaucoma: • Gonioscopy: To view the angle of Anterior Chamber. • Goldmann’s Applanation Tonometry: To measure the intraocular pressure (IOP).
Diagnostic Technique 1: Gonioscopy • Gonioscopy is a method to gain a view of angle of AC with the help of a goniolens and a slit lamp/ operating microscope. • In the Indirect Gonioscopy method, a contact lens is inserted between the lids to lie upon the anaesthetized cornea; fitted with a mirror placed at an angle of 62°-64°, in which the image of the recess of AC is reflected.
In the Direct Gonioscopy method, a dome shaped glass contact lens refracts light from angle of AC directly into observer’s eye (without any mirror); thus providing a much clearer view of the angle.
In the Indentation Gonioscopy method, the aqueous is displaced from the centre to the periphery so that iris is pushed backwards at the angle. It allows visualization of the angle of AC in case of a narrow angle [as in PACG].
Diagnostic Technique 2: Goldmann’s Applanation Tonometry: Basics • Applanation tonometry measures IOP by providing force which flattens the cornea. • It is based on Imbert-Fick law: Pressure within a sphere (P) is roughly equal to the external force (f) needed to flatten a portion of the sphere divided by the area (A) of the sphere which is flattened:P = f / A. • But this law applies to a perfect sphere (dry and thin walled) only.
Continued….. • However, the human eye is not thin walled and it is not dry, producing two confounding forces: (1) A force produced by the eye’s scleral rigidity (because the eye is not thin walled), directed away from the globe; and (2) A force produced by the surface tension of the tear film (because the eye is not dry), directed toward the globe.
A) When a flat surface is applied to the cornea with enough force (w) to produce a circular area of flattening greater than 3.06mm in diameter, the force caused by scleral rigidity (r) is greater than that caused by the tear film surface tension (s). (B) When the force of the flat surface produces a circular area of flattening exactly 3.06mm in diameter, the confounding forces caused by scleral rigidity and tear film surface tension cancel each other. The applied force (w) then becomes directly proportional to the intraocular pressure (p).
How does the observer know when the area of applanation is exactly 3.06mm in diameter so that the intraocular pressure can be measured? • The applanation tonometer is mounted on a biomicroscope to produce a magnified image. • When the cornea is applanated, the tear film, which rims the circular area of applanated cornea, appears as a circle to the observer. • The tear film often is stained with fluorescein dye and viewed under a cobalt-blue light in order to enhance the visibility of the tear film ring.
The clinician looks through the applanation head and adjusts the pressure until the half circles just overlap one another. • At this point, the circle is exactly 3.06mm in diameter, and the reading on the tonometer (multiplied by a factor of 10) represents the intraocular pressure in millimeters of mercury.
Types of PACG • PACG is of 3 different types: • Acute, • Subacute, • Chronic. • In acute PACG, there is sudden occlusion of the angle of AC and explosive rise in IOP with severe unilateral headache, diminution of vision and a red eye.
In subacute PACG, in a person with a shallow AC, some stress factors like watching TV for a long time/ rapid eye movement during sleep etc. causes a sharp rise in IOP with severe unilateral headache/ coloured halos/ blurring of vision. • Repeated subacute attacks of PACG leads to chronically elevated IOP and synechial closure; often designated as “Chronic PACG”.
Treatment Of Glaucoma • Line of treatment: • Remove precipitating factors (any drug that may elevate IOP, i.e., steroids etc.). • IOP Reduction by: • Medication(s), • Laser, • Surgery. 3. Correct the angle closure by: • Laser, • Surgery. 4. For secondary glaucoma, treat the underlying pathology.
