Pilots are very concerned about hypertension before a flight, during a flight, and before renewing their medical certificate. Our pathophysiology requires regulating many pressures. As pilots, we need to be cognizant of pressure altitude, lift in relation to dynamic pressure, Bernoulli, Newton, Navier-Stokes, and the bending of the wind. Our heart requires a blood pressure of around 130/80 mmHg to perfuse the brain, kidneys, eyes, and peripheral organs. The eyes need to be monitored for high intraocular pressure as we age.
The optic nerve is a conduit that transmits visual impulses from the retina to the brain’s visual cortex for interpretation. It contains over a million nerve fibers and is also responsible for eye reflexes, such as pupil dilation, and for maintaining your circadian rhythm. The optic nerve carries light-dark signals to the brain to help regulate a 24-hour circadian rhythm. The retina converts light into electrical impulses, which travel through the optic nerve to the brain. The brain then converts these impulses into perceptions of color, objects, and spatial depth.
There are two types of glaucoma. The most common type is open-angle glaucoma, which is treated in most cases with ophthalmic solutions. Acute angle-closure glaucoma requires an immediate reduction of severely elevated intraocular pressure (IOP) with medications and ophthalmic solutions. Once the IOP is decreased, a surgical procedure is performed to prevent further obstruction. Glaucoma is characterized by increased intraocular pressure (IOP). IOP is the pressure inside the eyeball. It is measured as the rate of flow of aqueous humor (the clear, watery fluid in the front chambers of your eye, between the cornea and the lens) divided by the rate at which the fluid drains from the eye. Aqueous humor delivers nutrients to the lens and cornea, which lack their own blood supply.Aqueous humor also transports away metabolic waste products from the front of the eye. High intraocular pressure damages the optic nerves, and this damage is irreversible. Optic nerve damage causes blind spots and, if left untreated, may lead to vision loss.
The goal of glaucoma therapy for primary open-angle glaucoma (POAG) is to reduce IOP by 20-30% from the baseline elevated IOP. If the IOP is very high, the goal is to decrease it by more than 30%. Target IOPs are continuously monitored to maintain tight control with ophthalmic eye drops. The American Academy of Ophthalmology glaucoma treatment standards emphasize individualized care. Pharmaceutical eye solutions should effectively lower IOP by decreasing aqueous humor production or increasing outflow, have no adverse side effects that exacerbate glaucoma, be administered once a day, and be inexpensive. Laser and surgical interventions are available if the ophthalmic solution(s) do not lower IOP. Once a medication is instituted, the full efficacy of therapy is usually observed within a month.
First-line ophthalmic eye solutions for POAG are prostaglandin analogs (PAs). The normal elimination pathway of aqueous humor is through a canal between the iris and cornea called the Schlemm’s canal. The aqueous humor then enters the bloodstream. If there is a blockage in the Schlemm’s canal, the IOP in the eye will increase. PA eye solutions will open the canal, increase aqueous humor drainage, and decrease IOP. As the name suggests, prostaglandin analogs remodel the tissue in the Schlemm’s canal. The mechanism of action of PAs is to bind to prostaglandin receptors in the eye. The most common side effect observed for PAs is photophobia (high sensitivity to light). There are two unique side effects of PAs. One side effect is a change in eye color. The color of the iris gradually turns brown. This effect is seen mostly in patients with blue-brown, green-brown, and gray-brown eye colors. Another unique side effect has been reported with the medication latanoprost (Xalatan), possibly thickening and darkening of the patients’ eyebrows. FAA-allowed PAs are travoprost (Travatan), latanoprost (Xalatan), latanoprostene bunod (Vyzulta), and bimatoprost (Lumigan). Travoprost and latanoprost can be approved with a CACI (Conditions AME Can Issue). Bimatoprost requires the glaucoma eye evaluation form, 8500-14 Special Issuance, if not qualified by CACI. Latanoprostene requires submission of an FAA eye evaluation form.
If PAs fail to lower IOP, secondary and adjunctive ophthalmic solutions are added to PAs or administered after discontinuing PAs. The next category of POAG ophthalmics prescribed is topical beta-blocker eye drops. The mechanism of action is the same as that of oral beta-blockers, which work on the heart to decrease blood pressure. The ciliary body, located behind the iris, produces aqueous humor. It contains beta receptors that respond to epinephrine (adrenaline). The more epinephrine that is stimulated, the more aqueous humor is produced. Too much aqueous humor increases IOP. By inhibiting beta receptors, aqueous humor production decreases. The recommended technique for administering eye drops is to hold your finger over the tear duct and, with your other hand, instill the drops. This is called punctal occlusion. Please wash your hands before using this technique. If beta-blocker eye drops enter the tear duct, they will be absorbed systemically and may cause bradycardia (slow heart rate). Other side effects include blurred vision, eye ache, and corneal anesthesia. FAA-allowed beta-blocker ophthalmics include timolol (Timoptic, Timoptic XE, Betimol, Ocumeter) , for which an AME can issue a CACI or, if qualified, an FAA eye evaluation form. Timolol/brimonidine (Combigan) requires an FAA glaucoma eye evaluation, and dorzolamide/timolol (Cosopt) allows an AME to issue a CACI or, if qualified, an FAA eye evaluation form.
Alpha2-agonist (A2A) ophthalmic agents have a dual mechanism of action in glaucoma. A2A eye solutions decrease aqueous humor production and increase drainage of aqueous from the eye into the circulatory system. Side effects include dry mouth, fatigue, and drowsiness. The most commonly used A2A is bromonidine (Alphagan-P). Apraclonidine (Lopidine) is also prescribed but may have a higher incidence of allergic reactions than bromonidine. FAA-allowed A2As include bromonidine/brinzolamide (Simbrinza), which requires an FAA eye evaluation form, and brimonidine (Alphagan-P), for which an AME can issue a CACI or, if qualified, an FAA eye evaluation form.
Carbonic anhydrase inhibitor (CAI) ophthalmic solutions reduce aqueous humor production in the ciliary body. Brinzolamide (Azopt), dorzolamide (Trusopt), brimonidine/brinzolamide (Simbrinza), and dorzolamide/timolol (Cosopt) are the most commonly prescribed CAIs for POAG. If CAIs are prescribed alongside other glaucoma eye solutions, the patient must administer each topical solution ten minutes apart. Side effects of CAIs include temporary blurred vision, a bitter, sour, or unusual taste in the mouth, and dry eyes. Brinzolamide, dorzolamide, and dorzolamide/timolol are CAIs for which an AME can issue a CACI or, if qualified, an FAA eye evaluation form. Bromonidine/brinzolamide requires an FAA eye evaluation form.
In December 2017, the FDA approved netarsudil (Rhopressa), a first-in-class rho kinase inhibitor /norepinephrine transport inhibitor for POAG. Netarsudil increases aqueous outflow from the eye to decrease IOP. Its mechanism of action relaxes the trabecular meshwork (the spongy tissue inside the eye that drains aqueous humor), improves fluid drainage, lowers eye pressure, and reduces the production of aqueous humor. The cost of Rhopressa is between $330 and $413 without insurance. With some commercial insurers, the cost can be as low as $30. FAA approval for Rhopressa is on a case-by-case basis, with a Special Issuance.
Comprehensive baseline eye exams are recommended for everyone starting at age 40. Relying solely on reading an eye chart at 20 feet during an annual physical is not enough to detect the early signs of glaucoma. If we do not catch glaucoma early, the risk of losing our eyesight increases. Please get an annual eye checkup with your ophthalmologist or optometrist if you are over 40. The sweet sound of hearing a pilot say “traffic in sight” is music to my ears. Be safe and fly well.
