What to Expect at Your First Eye Exam

07 Dec What to Expect at Your First Eye Exam

The eye is a complex organ that manipulates light much like a camera does; it has lenses to change the focus and a sensor to recognize intensity and color.

How Does the Eye Focus? Starting with the Cornea

The first layer of the eye that light hits is the cornea, the surface of the eye. The cornea is a dome-shaped lens that starts the process of focusing light, contributing approximately two-thirds of the eye’s focusing power. But the cornea is like the lens of eyeglasses – it always refracts light the same amount, unlike the lens of a camera which can focus at different depths.

The shape of the cornea is maintained by the aqueous humour, a gel that lies between the cornea and the lens.

The Pupil and Iris Regulate Amount of Light

The iris is the colorful part of the eye. The pupil, the black spot in the middle of the iris, is actually just a hole in the iris, which can contract or relax to adjust the size of the pupil. In low light, the pupil expands to allow more light into the eye. In bright light, it contracts to protect the eye and increase contrast.

The Lens Focuses Light

Regular visits to an eye doctor are an important part of maintaining your health, but many people don’t start going until they notice a problem. If you are an adult going to your first eye exam, your first appointment with a new eye doctor, or your first visit in a long time, here is what you can expect.

Medical History

To start, you will be asked for your medical history, either through a paper or electronic questionnaire or in person. This questionnaire can be quite detailed and includes your family medical history. It will ask particularly about chronic conditions, like diabetes or heart disease, even if they don’t relate directly to your eyes. Double-check your family’s medical history before you go. Knowing what conditions are in your family can help the doctors know what you might be at risk for, both for conditions that affect eyesight and for other, non-vision-related diseases that can be detected by eye exams.

You will also be asked to provide a thorough history of your eye health and care. If you have seen an ophthalmologist or optometrist in the past, it is helpful if you can obtain your records from previous doctors and bring a copy with you.

Eye Tests

Your first eye exam will include tests designed to evaluate your ocular health, check for diseases, and measure your visual acuity (quality of sight). Here are some of the tests that are often used, according to the Mayo Clinic.

• Visual acuity test: In this common test, you will be asked to read letters on a chart. The letters range in size from large at the top to very small at the bottom. The ability to read letters on a particular line gives a preliminary indication of what prescription you might need for vision correction.
• Refraction assessment: If your visual acuity test indicates that you would benefit from vision correction, the doctor will have you continue to look at the letters through refractive lenses. These lenses are similar to the lenses in glasses, and the doctor can check a variety of options to see which are best for your eyes.
• Manual vision field testing: The brain is very good at filling in any blank spots in your vision; this test is designed to find them. A light will flash on a screen and you press a button if you can see it; doing this repeatedly in different spots generates a map of the blanks in your vision.
• Slit-lamp examination: The slit lamp shines a bright but painless light into one eye. It allows the doctor to examine your eye through a magnifying glass to check for abnormalities that can indicate diseases.
• Indirect ophthalmoscopy: A test to look at the inside back of your eye. Similar to the slit-lamp examination, the doctor uses an instrument worn on her head and directs the light through a lens held close to your eye.
• Applanation tonometry: The doctor analyzes the pressure of your eye by measuring how much force is required to flatten a section of the cornea, using a small rod with a flattened cone at the tip. It contacts the eye gently and is not painful. This test evaluates your risk for glaucoma. Alternately, a puff of air may be used; this is call noncontact tonometry and is surprising, but also painless.

With these tests, your doctor can fully evaluate the health of your eyes. After your first eye exam, be sure to go regularly—checking your eyes is just as important as a normal checkup.

For questions or comments, contact Woodhams Eye Clinic.

A healthy lens is critical to good vision. As people age, the lens can become cloudy, causing a cataract, or stiff, causing presbyopia. When the lens becomes stiff, the cilliary muscles can no longer change the shape of the lens to focus on up close objects.

The Retina Detects Light

From the crystalline lens, light travels through another gel known as the vitreous humor, which maintains the shape of the eye, to the retina in the back of the eye. The retina contains light-receptor cells known as rods and cones. Rods are very sensitive and simply detect light, giving us our nearly-colorless night vision, while cones detect different colors. Cones are concentrated in the fovea, a pit in the center of the retina, providing very sharp central vision.

Oddities of the Retina: Flipped and Holey

The lens projects an image onto the retina, but it is rotated 180 degrees (upside down and backwards). If you flip upside down to watch a movie, what you see is actually what is being projected onto the retinas of your bemused friends. This is because the shape of the lens causes light to converge through a single point inside the lens, emerging out the back like light leaving a projector.

There is also a gap in your vision known as the blind spot, where blood vessels and nerves pass through the retina. So why don’t you see a flipped world with a hole in it? The brain corrects for both of these, providing you with a properly oriented image and filling in the blind spot with the surrounding color.

To recap: light is partially focused when it passes through the cornea, then travels through the aqueous humour to the crystalline lens, which lets the eye focus on different depths. The light converges in the lens and travels out the other side flipped, traveling through the vitreous humour to the retina on the inner back surface of the eye, where rods and cones detect light. Then your brain presents a coherent, correctly-oriented image.

Ready for the test?