KNOWLEDGE

AGE-RELATED MACULAR DEGENERATION
 

Age-related macular degeneration (ARMD) is a progressive disease affecting the macula, the central part of the retina which allows us to see details. 

One in seven people over the age of 50 will get  ARMD and is the leading cause of poor vision in the elderly. It leads to a progressive loss of central vision, which is needed for activities like reading, recognising faces, and driving. 

The macula is located in the centre of the retina, in the optical axis of the eye. Owing to its central position, the macula transmits 90% of the visual information handled by the eye, and is responsible for detailed vision. 

There are two forms of macular degeneration: 

  • Atrophic (the macula atrophies progressively with age and is replaced with scar tissue. It is the most common and least severe form of the disease, and it progresses over many years) and 

  • Exudative (small blood vessels develop newly under the macula that bleed easily leading to haemorrhages in the back of the eye. This bleeding may eventually result in macular scarring causing rapid and profound vision loss)

 

In initial stages you will notice a few signs such as pain, redness, or loss of visual acuity. During this time, only ophthalmological examinations and OCT scans permit diagnosis of the disease. In the advanced stages you may notice: 

  • Decrease in visual acuity, necessitating increased lighting for activities such as reading and precision work.

  • Progressive blurriness of central vision, alteration of colour perception, and distortion of straight lines, which may appear deformed and wavy.

  • Appearance of dark spots in the central field of vision, difficulties recognising faces, visual hallucinations, or a severe loss of visual acuity.
     

An OCT scan (see scans to the right) allows us to look at a cross section of the macula and determine if the delicate structures of the macular are beginning to split. 

 

Early detection is the key at which point ARMD has a greater chance of successful treatment! 

Brett Howes your Mercury Bay Optometrist has an OCD scanner at the practice in Whitianga. Talk with Brett about having your OCT scan done. It is important!

HOW YOUR EYES WORK
 

Vision begins when light rays are reflected off an object and enter the eyes through the cornea, the transparent outer covering of the eye. The cornea bends or refracts the rays that pass through a round hole called the pupil. The iris, or coloured portion of the eye that surrounds the pupil, opens and closes (making the pupil bigger or smaller) to regulate the amount of light passing through. The light rays then pass through the lens, which actually changes shape so it can further bend the rays and focus them on the retina at the back of the eye. The retina is a thin layer of tissue at the back of the eye that contains millions of tiny light-sensing nerve cells called rods and cones, which are named for their distinct shapes. Cones are concentrated in the centre of the retina, in an area called the macula. In bright light conditions, cones provide clear, sharp central vision and detect colours and fine details. Rods are located outside the macula and extend all the way to the outer edge of the retina. They provide peripheral or side vision. Rods also allow the eyes to detect motion and help us see in dim light and at night. These cells in the retina convert the light into electrical impulses. The optic nerve sends these impulses to the brain where an image is produced.

WHAT HAPPENS IN AN EYE EXAMINATION
 
  • An eye muscle movement test: To test muscle strength and control, the optometrist will ask you to visually track a target in different directions and observe your eye movements.

  • Cover test: This is a check for how well your eyes work together. As you stare at a small target some distance away, the optometrist will cover and uncover each eye to observe how much your eyes move, watching for an eye that turns away from the target (strabismus). The test may be repeated with a target close to you.

  • External exam and pupillary reactions: The optometrist will watch the reactions of your pupils to light and objects at close distance. At the same time, the optometrist will check the exterior eye, looking at things such as the condition of the white of the eyes and the position of your eyelids.

  • Visual acuity test: You'll sit in front of an eye chart, with letters that get smaller as you read down each line. You cover each eye in turn and, using the other eye, read aloud, going down the chart, until you can't read the letters anymore.

  • Retinoscopy: The optometrist may shine a light in your eyes and flip lenses in a machine (phoropter) that you look through while staring at a large target, such as a big "E". By checking the way light reflects from your eyes, the optometrist gets an approximate idea of the lens prescription you need now.

  • Refraction testing: For your exact lens prescription, the optometrist may fine-tune the prescription manually by asking you to respond to questions such as, "Which is better, this or that?" while flipping back and forth between different lenses. If you don't need corrective lenses, you won't have this test.

  • Slit lamp (biomicroscope): The slit lamp magnifies and lights up the front of your eye. The eye doctor uses it to detect several eye diseases and disorders by examining your cornea, iris, lens, and anterior chamber.

  • Retinal examination (ophthalmoscopy): Using an ophthalmoscope and pupil dilation, the optometrist examines the back of your eyes: retina, retinal blood vessels, vitreous, and optic nerve head.

  • Glaucoma testing: This tests whether the fluid pressure inside your eyes is within a normal range. Painless and taking just a few seconds, the test can be done several ways.

  • The tonometer test: This is the most accurate. With drops numbing your eyes, you stare directly ahead. The optometrist barely touches the front surface of each eye with an instrument to measure the pressure.

  • The "puff of air" or non-contact tonometer test: While you focus on a target, you get a small "puff" of air in each eye. Resistance to the air puff indicates the pressure.

  • Pupil dilation (enlargement): With your pupils fully enlarged, the optometrist will examine the inside of your eyes with different instruments and lights. The pupil-enlarging drops for this part of your eye exam start to work after about 20-30 minutes, making your eyes more sensitive to light and blurring your vision. These effects may last for several hours or longer so it's important to bring a pair of sunglasses to your exam for the ride home.

  • Visual field test : Your visual field is the area you can see in front of you without moving your eyes. Using one of three tests, the eye doctor "maps" what you see at the edges (periphery) of your visual field, using this map in diagnosing your eye condition.

HOW DIABETES AFFECTS VISION
 

Although individuals with diabetes are more likely to develop cataracts at a younger age and are twice as likely to develop glaucoma as are non-diabetics, the primary vision problem caused by diabetes is damage to the retina (Diabetic retinopathy), the leading cause of new cases of blindness and low vision in adults aged 20-65:

The retina is a thin, light-sensitive tissue that lines the inside surface of the eye. Nerve cells in the retina convert incoming light into electrical impulses. These electrical impulses are carried by the optic nerve to the brain, which interprets them as visual images. Diabetic retinopathy occurs when there is damage to the small blood vessels that nourish tissue and nerve cells in the retina.

Symptoms of diabetic retinopathy can include:

 

  • Blurred or double vision

  • Flashing lights, which can indicate a retinal detachment

  • A veil, cloud, or streaks of red in the field of vision, or dark or floating spots in one or both eyes, which can indicate bleeding

  • Blind or blank spots in the field of vision
     

CATARACTS
 

A cataract is a clouding of the eye's natural lens, which lies behind the iris and the pupil. Cataracts are the most common cause of vision loss in people over age 40 and is the principal cause of blindness in the world. 

A cataract starts out small and at first has little effect on your vision. You may notice that your vision is blurred a little, like looking through a cloudy piece of glass or viewing an impressionist painting. A cataract may make light from the sun or a lamp seem too bright or glaring. Or you may notice when you drive at night that the oncoming headlights cause more glare than before. Colours may not appear as bright as they once did.

What Causes Cataracts? The lens inside the eye works much like a camera lens, focusing light onto the retina for clear vision. It also adjusts the eye's focus, letting us see things clearly both up close and far away. The lens is mostly made of water and protein. The protein is arranged in a precise way that keeps the lens clear and lets light pass through it. But as we age, some of the protein may clump together and start to cloud a small area of the lens. This is a cataract, and over time, it may grow larger and cloud more of the lens, making it harder to see. If you think you have a cataract, see Mercury Bay Optometrist for an exam to find out for sure.
 

@2016 Mercury Bay Optometrist

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