Goldmann Applanation Tonometry is a widely recognized method used to measure the pressure inside the eye, known as intraocular pressure (IOP). It is considered a standard in eye care due to its accuracy and reliability. The procedure involves gently flattening a small area of the cornea, the clear front surface of the eye, to determine the force required to achieve this flattening. This measurement provides an indirect assessment of the fluid pressure within the eyeball.
Purpose of the Procedure
Goldmann Applanation Tonometry measures intraocular pressure, a key factor in detecting and managing eye conditions. The primary reason for this test is to screen for and monitor glaucoma, a group of eye diseases that can lead to irreversible vision loss if left untreated. In most cases of glaucoma, the fluid that normally circulates within the eye drains too slowly, causing pressure to build up. Elevated IOP can damage the optic nerve, which transmits visual information from the eye to the brain, eventually leading to vision impairment.
Regular IOP measurements help eye care professionals identify individuals at risk for glaucoma, especially those over 40 or with a family history. This test also helps assess the effectiveness of treatments aimed at lowering eye pressure in patients diagnosed with glaucoma or ocular hypertension, a condition where IOP is higher than normal without immediate optic nerve damage. Early detection and consistent monitoring allow for timely intervention, which can help preserve vision and slow the progression of the disease.
The Examination Process
Before the procedure, your eye care provider will administer numbing eye drops to ensure comfort. A small amount of fluorescent dye, like fluorescein, is also applied to the eye. This dye helps the eye care professional visualize the tear film and the area of contact during the measurement.
You will then rest your chin on a chin rest and your forehead against a bar on a specialized microscope called a slit lamp, which helps keep your head steady. The eye care professional will gently hold your eyelids open to prevent blinking. The tonometer, attached to the slit lamp, has a small, flat-tipped probe that is moved forward until it lightly touches the center of your cornea.
Looking through the slit lamp, the eye care professional will observe two glowing green semicircles formed by the fluorescein. They will then adjust a dial on the tonometer until the inner edges of these semicircles align, and the intraocular pressure reading is taken from the dial in millimeters of mercury (mmHg). The entire process is quick, lasting only a minute or two, and is usually painless due to the numbing drops.
Interpreting Your Results
Results are provided as a numerical value in millimeters of mercury (mmHg). A typical “normal” intraocular pressure range for healthy individuals is generally considered to be between 10 and 21 mmHg. Most healthy people have an IOP within this range.
An elevated reading, particularly above 21 mmHg, may indicate ocular hypertension or an increased risk for glaucoma. However, a single high reading does not automatically mean you have glaucoma, as various factors can influence IOP. Your eye care professional will interpret your results in conjunction with other diagnostic tests, such as an examination of the optic nerve and visual field tests. This comprehensive approach helps determine if further investigation or treatment is necessary, allowing for a personalized target IOP range to minimize the risk of optic nerve damage.
Important Considerations and Safety
Before undergoing Goldmann Applanation Tonometry, inform your eye care provider if you have a history of corneal ulcers, eye infections, or allergies to anesthetic drops. If you wear contact lenses, remove them before the test. Wearing loose-fitting clothing is also helpful, as tight collars or ties can sometimes influence IOP readings.
Following the procedure, you might experience minor and temporary side effects, including slight blurring of vision, temporary yellowing of the skin around the eyes from the fluorescein dye, or mild irritation. There is a small possibility of a corneal abrasion, a superficial scratch on the cornea, which typically heals within a few days. The procedure is generally considered safe, and proper disinfection of the tonometer probe between patients helps prevent disease transmission.
Several factors can influence the accuracy of IOP readings. Corneal thickness is one factor; thicker corneas may result in artificially higher readings, while thinner corneas can lead to artificially lower readings. Other factors include corneal astigmatism, excessive tear production, and the time of day, as IOP naturally fluctuates throughout a 24-hour period, often being highest in the early morning. Patient anxiety or holding one’s breath during the test can also temporarily elevate readings. Regular eye examinations that incorporate tonometry are important for early detection and ongoing monitoring of eye health.