We often talk about importance of getting an eye checkup or an eye examination according to individualized needs. There is a long list of eye tests which can be done to either screen for diseases, assess risks for developing diseases, diagnose abnormalities or pick up vision threatening conditions. Sometimes, a blood tests or blood pressure reading may also be taken in order to lookout for systemic co-morbidities which can increase risk of vision loss. Today, let’s have a look at some of the tests and equipment which we commonly use to screen or diagnose eye problems.
Visual Acuity Test
The measurement of your ability to differentiate shapes and details of objects you see are referred to as visual acuity test. It is just a part of your overall vision, however, visual acuity test would probably the first eye exam done when you walk into an eye clinic.
One of the common method to determine visual acuity would the Snellen’s test or Tumbling E. These tests use a chart consists of letters or symbols of various sizes. You’ve probably seen the chart in general practitioners’ or optometrists’ office.
During the test, you’ll be required to cover one of your eye and read out loud the letters you see with your uncovered eye. You may be seated or standing while performing the test. Typically, the eye care personnel or optometrist will ask you to identify or read from the top until you can no longer accurately distinguish letters (the letters or objects gets gradually smaller as you go lower).
The pressure in the eye is called intraocular pressure (IOP). IOP higher than normal range is consider ocular hypertension. We often use a device called tonometer to measure the pressure in the eye. This is one of the screening tests for glaucoma, which is of the leading cause for blindness for people over the age of 60. By taking the measurement of intraocular pressure, we are able to screen and monitor conditions like glaucoma, post-refractive surgery / LASIK keratoconus, irregular or thin corneas and Fuch’s dystrophy.
Perimetry (Visual Field Test)
This equipment assesses the field of vision. This test is also referred to as visual field test, where loss of patient’s peripheral vision is detected and mapped. In other words, it measures how much can you see out of the corners of your eyes while your eye focused at the center. By referring to the perimety results, we would be able to evaluate glaucoma, some retinal diseases and neurological conditions.
During the test, subjects have to focus on the center of the display and indicate using a clicker when targets appear in the outer field of vision. The targets are often one or more spots of light appearing randomly at various positions on the display to asses if the subject can see it.
Retinal Camera / Fundus Photograph
One of the best way to view, screen, assess and monitor diseases affecting the back of the eye is by taking a Fundus photograph using a retinal camera. This device enables us to have detailed pictures of the structure and appearance of the posterior section of the eye (the back or the eye). We can detect minor changes in the eye over time and take timely action to prevent vision loss and preserve vision.
Various anomalies which can causes eye diseases or vision threatening conditions can be detected, documented and monitored. Fundus photo is particularly useful in diagnosing and treating diabetic retinopathy, glaucoma, age-related macular degeneration (AMD) among many others. The fundus photo is also very useful when we want to explain the prevailing conditions to patients.
Optical Coherence Tomography (OCT Scan)
Optical coherence tomography (OCT) is a non-invasive, imaging test which uses light waves without radiation to take a three-dimensional (3D) cross section of the retina. This allows the ophthalmologist to analyze each layer of the retina. Yes, the retina consists of many layer!
This eye scan is fast, non-invasive and painless for the patient. We use them to scan for early diagnosis of many serious eye conditions that may develop with no noticeable signs and symptoms. Once diagnosis is confirmed, we can use this device monitor disease progression or regression as well as treatment success or recurrences. It is particularly useful for seeing retinal detachments (a serious eye emergency!), macular degeneration, diabetic eye disease, retinal vein occlusion, glaucoma and many others.
Slit Lamp Examination
The slit lamp allow us to have a magnified, 3-D view of your eyes. This device is very useful particularly to observe the anterior segment (front of the eye) which includes the sclera, cornea, lens, iris and the front section of the gel-like fluid that fills the large space in the middle of the eye.
We also often use special lenses with the slit lamp to view structures further into the eye (back of the eye), such as the optic nerve and the retina. The slit lamp helps us to detect many condition throughout the eyes and more often than not to identify foreign object. Sometimes we may have to dilate your pupils using eye drops to have a better view inside your eyes.