Opthalmology

• Glaucoma is a diverse group of disorders with a potentially progressive optic neuropathy associated with visual field loss as damage progresses, where IOP is a key modifiable factor
• Normal IOP is approximately 10-21 mm Hg, with the general population skewed towards higher pressures
• An IOP screening value in the early 20s mm Hg without optic nerve and visual field changes is called ocular hypertension
• Normal or low-tension glaucoma can occur with initial screening IOPs below 21 mm Hg
• Aqueous is produced from plasma by the ciliary epithelium of the ciliary body pars plicata through active and passive secretion
• Aqueous flows from the posterior chamber via the pupil into the anterior chamber and exits the eye through trabecular outflow, uveoscleral drainage, and the iris
• Tonometry is the measurement of IOP, with Goldman applanation tonometry being the most common form
• Fundoscopy is used to evaluate the optic nerve head in glaucoma, with an increase in cup/disc ratio being a major sign
• Pachymetry measures corneal thickness, affecting the estimation of IOP
• Gonioscopy is used to evaluate the anterior chamber angle, classifying glaucoma into open or closed angle
• Perimetry is the systematic measurement of visual field function, with glaucoma typically resulting in loss of peripheral visual field first
• Primary Open Angle Glaucoma (POAG) is the most common form, characterized by IOP > 21 mmHg at some stage, optic nerve damage, and visual field loss
• Normal tension glaucoma (NTG) is a variant of POAG with consistently equal to or less than 21 mmHg IOP
• Primary Angle-Closure Glaucoma (PACG) refers to the occlusion of the trabecular meshwork by the peripheral iris obstructing aqueous outflow
• Symptoms of glaucoma can be asymptomatic or include blurring, halos, decreased vision, redness, ocular pain, and headache
• Management of glaucoma includes medical, laser, and surgical options, with the goal of lowering IOP to reduce progression
• Secondary glaucoma refers to any form with an identifiable cause of increased eye pressure, resulting in optic nerve damage and vision loss
• Pseudoexfoliation (PXF):

  • Grey-white fibrillary amyloid-like material may deposit on the endothelium, in the AC, iris, lens, zonules, and anterior chamber angle
  • Common cause of secondary open-angle glaucoma
  • Prevalence increases after the age of 50
  • Common in Scandinavians
  • Cataract more common than average, lens instability may be present
• Neovascular glaucoma (NVG):

  • Occurs due to aggressive iris neovascularization caused by severe, diffuse, and chronic retinal ischemia
  • Causes include ischemic central retinal vein occlusion, diabetes mellitus, arterial retinal vascular disease, ocular tumors, long-standing RD, chronic intraocular inflammation
  • Glaucoma initially caused by blood vessels impairing aqueous outflow in the presence of an open angle, progressing to severe secondary synechial angle-closure glaucoma
• Inflammatory glaucoma:

  • Mostly occurs in chronic and severe uveitic diseases, particularly in Fuch's uveitis and uveitis associated with juvenile idiopathic arthritis
  • Can cause secondary open-angle glaucoma due to trabecular obstruction by inflammatory cells and debris, or secondary to acute trabeculitis or trabecular scarring
  • Can cause secondary angle closure with or without pupillary block due to posterior or anterior synechiae
• Primary congenital glaucoma (PCG):

  • Rare with an incidence of 1:10000 in many populations
  • More common in Saudi Arabia (1:2500) compared to the UK (1:20000)
  • Boys are more commonly affected than girls
  • Involvement is more often bilateral
  • Caused by impaired aqueous outflow due to maldevelopment of the anterior chamber angle (trabeculodysgenesis)
  • Prognosis dependent on severity and age at onset/diagnosis, with legal blindness in at least 50% of eyes in true congenital glaucoma
• Diagnosis of PCG:

  • Presentation includes corneal haze, buphthalmos, asymmetrical eyes, watering, photophobia, or blepharospasm
  • Corneal haze, buphthalmos, Haab striae, corneal scarring and vascularization, optic disc cupping
  • Evaluation under GA for IOP measurement, anterior chamber and gonioscopic evaluation, corneal diameters measurement, refraction, and optic disc examination
• Treatment of PCG:

  • Management is essentially surgical; medications may be used as temporary or supplemental therapy
  • Surgical options include goniotomy, trabeculotomy, trabeculectomy, tube shunt implantation, and ciliary body ablative procedures
  • Monitoring of IOP, corneal diameter, and other parameters required long-term, mostly under general anesthesia
  • Amblyopia and refractive errors should be managed aggressively
• Medical management in glaucoma:

  • Topical agents work by decreasing production of aqueous, increasing its drainage, or both
  • Prostaglandin derivatives (e.g., latanoprost), beta-blockers (e.g., timolol), alpha-2 agonists (e.g., brimonidine), carbonic anhydrase inhibitors (e.g., dorzolamide), miotics (e.g., pilocarpine)
  • Systemic agents like carbonic anhydrase inhibitors (e.g., acetazolamide) and osmotic agents (e.g., IV mannitol)
• Surgery in glaucoma - Trabeculectomy:

  • Lowers IOP by creating a fistula to allow aqueous outflow from the anterior chamber to the sub-tenon space
  • Indications include failure of conservative therapy, progressive deterioration, advanced disease, patient preference
  • Complications include pupillary block, over-filtration, malignant glaucoma, failure of filtration, late bleb leakage, bleb-associated infections
• Drainage shunts:

  • Glaucoma drainage devices create a communication between the anterior chamber and the sub-tenon space
  • Indications include severe conjunctival scarring, uncontrolled glaucoma, certain congenital glaucoma
  • Complications include excessive drainage, malposition, tube erosion, corneal decompensation, double vision, early and late drainage failure