Our eyes are filled with fluid called aqueous, that helps keep them inflated like a ball. Normal eye pressure can change throughout the day and vary from person to person. In healthy eyes, this fluid drains constantly to keep the eye pressure steady.
If your eye pressure is high and your eyesight is regularly deteriorating, it could be a sign that the optic nerve of your eyes is gradually getting damaged.
A tonometry test checks your eye pressure by putting a pressure gauge on your eyeball. It checks the firmness of your eyeball and is measured in the same units as checking your blood pressure. The normal range for IOP (intraocular pressure) is 10-20 mm Hg.
Intraocular Pressure Changes Following Diagnostic Pupillary Dilation With Cyclopentolate
Acute rises in intraocular pressure (IOP) have been known to occur with the use of some cycloplegic agents, and it has been recognized that a narrow irido-corneal angle can predispose to this effect. Gonioscopy has allowed us to identify the cause of these acute rises in IOP.
More recently, significant rises in IOP have been found to occur in eyes with no obvious narrowing of the angle of their anterior chamber.
These patients had decreased aqueous outflow, which occurred simultaneously with increased IOP.
Further studies show that the key factor in determining high levels of eye pressure is changes in aqueous formation.
Elevation of Eye Pressure Following Dilatation
This is a common finding in glaucoma patients, and is linked to their progression of visual field loss.
The exact mechanism of the elevation in eye pressure is unknown, but it seems that it is related to the narrowing of the angles of the eye.
Pupillary dilation leads to a temporary drop in the rate of flow of aqueous humor, which causes a rise in intraocular pressure. This effect in most of the people, can be seen for several hours or sometimes, even days after eye dilation.
Acute pressure elevation occurs in narrow angle glaucoma patients.
During a dilated eye exam, when eyes are dilated with a mydriatic drug, patients who have open angle glaucoma, can also have an increase in intraocular pressure. Blurry vision after dilation is an indication that the eye pressure has increased.
One study found that 48% of eyes with open-angle glaucoma had a rise in intraocular pressure (IOP) when dilated with 10% phenylephrine.
Another study revealed that approximately 23% of patients with primary open angle glaucoma had a significant rise in intraocular pressure (IOP) after administration of cycloplegics.
A scientist, Lee found that pupil dilatation could increase intraocular pressure in certain patients.
Researchers have determined that the IOP rises the fastest between 45 and 120 minutes after drops of cyclopentolate are given; however, it can last for several hours if left untreated.
The mechanism by which the increased pressure in the eye results isn’t known, but it could result from pigment liberation into the anterior chamber and subsequent obstruction of the trabecular meshwork.
Or, it could also result from decreased pull on the trabecular meshwork because of ciliary muscle paralysis, leading to a drop in aqueous outflow.
The Importance of Dilated Eye Exam
For a complete eye exam, pupillary dilation is done to expand the size of the pupils in order to help doctors see all the details of the eyes and optic nerve. During the dilated eye exam, they make sure that everything is okay, especially the optic nerve and retina.
Many causes of poor vision can be explained with the diseases and conditions of retina and optic nerve. Therefore, regular eye exam with dilation of the eyes is important. Your poor visual acuity is a good guide as to how frequently your eyes should be examined.
For people with glaucoma, especially those who are likely to develop acute glaucoma, pupil dilation should be performed with utmost care and under the supervision of an ophthalmologist or an optometrist.
How Long Does Dilation Last?
Dilation lasts, on average, from 4 to 24 hours, according to the American Association for Pediatric Ophthalmology and Strabismus.
An ophthalmologist normally instills two types of drops into your eyes. One type of drop is used to dilate your pupil, so that it becomes bigger. This drop is called Phenylephrine. The dilation with this lasts only for a few hours.
The second type of medication is the one which is used in relaxing the ciliary muscle (a circular muscle which changes the power of the lens) of the eye are the “cycloplegics”. An example of this type of medication is cyclopentolate. Dilation with this lasts for one to two days.
If you are having your eyes dilated for the first time, you should be mentally prepared to experience some visual blurriness and glare. Make sure to have a ride home by someone and bring sunglasses to help prevent light sensitivity.
As mentioned above, there’s a connection between persistent elevated IOP and the risk of developing glaucoma.
The potential long-term consequences of intraocular pressure rise include retinal vascular occlusion, anterior ischemic optic neuropathy, which could be sight threatening. It is important to recognize people who are susceptible to this rise in intraocular pressure and subsequent risk of glaucoma.
Important Points to Keep in Mind
1. Intraocular pressure rises with eye dilation, no matter which type of glaucoma the patient has.
2. Optic nerve damage does not occur immediately after elevation in eye pressure. It occurs only when the IOP stays high for a long time (days, weeks, months).
3. All adults should have a complete eye exam by the age of 40. If you don’t have any eye issues and aren’t at high risk for them, schedule a complete eye exam every two years.
4. Pupil dilation should be avoided completely in patients with advanced cupping and/or severe visual field loss. These patients cannot tolerate a marked elevation of IOP.
Having found that pharmacological pupillary dilation affects the likelihood of future progression of open-angle glaucoma in patients with glaucoma, we can conclude that the size of the increase in IOP induced by this treatment is related to the likely course of glaucoma.
In most of the people without glaucoma, the elevation of eye pressure caused by pupillary dilation is usually harmless.