Summary
Highlights
The eye is responsible for vision, receiving and focusing light to send to the brain via the optic nerve. Key parts include the eyelid, pupil, iris, cornea, lens, aqueous humor, sclera, ciliary body, choroid, retina (macula, rods, cones), and vitreous humor. Each part plays a specific role, such as the eyelid for protection, pupil for light regulation, and the lens for focusing vision.
Aqueous humor controls intraocular pressure (IOP), constantly produced by the ciliary body and draining into the canal of Schlemm. Normal IOP is 10-21 mmHg. Pupil constriction widens the canal of Schlemm, facilitating fluid drainage and reducing IOP, while dilation narrows it, increasing IOP. Factors like Valsalva maneuver, sneezing, coughing, and sucking through a straw can temporarily increase IOP.
Glaucoma is characterized by damage to the optic nerve (cranial nerve II), primarily due to decreased drainage of aqueous humor, leading to increased IOP. This elevated pressure can progressively lead to optic nerve damage and vision loss. Normal IOP is 10-21 mmHg, but in glaucoma, it can range from 22-29 mmHg (chronic) to 50-70 mmHg (acute).
Glaucoma is diagnosed using a tonometer to measure IOP, with tonometry being the confirmatory test. Initial signs include increased IOP, described as a feeling of fullness in the eye, discomfort, and decreased accommodation. The pathognomonic sign is peripheral vision loss, or 'tunnel vision'. Pain is a late sign, especially in acute glaucoma, often accompanied by halos around lights due to corneal edema.
Management focuses on avoiding activities that increase IOP, such as coughing, sneezing, straining (Valsalva maneuver), vomiting, prone positions, and heavy lifting (over 10 lbs). Patients are advised to lie on the non-operative side post-surgery. Antiglaucoma medications are administered to decrease aqueous humor production and enhance its outflow, promoting pupil constriction to widen the canal of Schlemm.
Open-angle glaucoma involves an open drainage angle but obstructed outflow, causing a slow and painless increase in IOP, thus classified as chronic and stable. Angle-closure glaucoma involves a completely closed drainage angle, leading to a rapid, painful increase in IOP, considered an acute emergency condition that can cause permanent vision loss if not addressed quickly.
Antiglaucoma medications like timolol, latanoprost, and brimonidine reduce aqueous humor production and enhance outflow. To prevent systemic absorption of eye drops, patients should apply gentle pressure to the inner canthus (punctal occlusion) for 1 minute. Anticholinergic medications are contraindicated as they cause pupil dilation, worsening the condition. Surgical options for open-angle glaucoma include iridectomy (removing part of the iris) and trabeculectomy (removing trabecular meshwork) to improve outflow. For acute angle-closure glaucoma, IV mannitol and hyperosmotics are used to rapidly decrease IOP in preparation for emergency surgery. Miotics like pilocarpine are commonly used to constrict pupils and improve drainage.
Clients should use eye drops as prescribed; remove contact lenses, wait 15 minutes after administration before reinserting; and follow proper administration steps. This includes shaking medication, tilting the head back, pulling down the lower eyelid, instilling drops without touching the eye, and performing punctual occlusion for 1 minute to prevent systemic effects. If multiple eye drops are prescribed, wait 5-10 minutes between installations to prevent dilution.