WHAT IS DEPTH PERCEPTION?

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WHAT IS DEPTH PERCEPTION?

Did you know that like most standard eye tests, the Snellen test does not check one’s depth perception? Read on to learn more about the tests that specifically check your depth perception.

When it comes to seeing the world in three dimensions (3D), depth perception plays a crucial role. Without it, there’s no way we can recognize distances between people and/or objects in all directions. Many experts explain that animals are able to sense the distance of objects (depth sensation) within their environments. However, the term perception is reserved for humans, since we are able to tell each other about the experiences of distance.

By definition, depth is looking into a hole or tube and estimating forward distances. To do this accurately, one must have binocular stereoscopic vision, or stereopsis. If someone lacks stereopsis, perceiving depth may be more difficult and less accurate, and they must rely on visual cues other than stereopsis.

Our eyes use three methods to determine distance:

The size a known object has on your retina – Knowing the size of an object due to previous experience helps our brains calculate the distance based on the size of the object on the retina.

Moving parallax – A great example of this is standing face to face with someone and moving your head side to side. The person in front of you moves quickly across your retina, but the objects that are further away don’t move very much at all. This helps your brain calculate how far or close something is from you.

Stereo vision – Since our eyes are about two inches apart, each eye receives a different image of an object on its retina, especially when an object is close up. When the object is far away, this method doesn’t work as well since objects appear more identical when further away from your eyes.

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WHEN LIVING NEAR THE WATER IS BAD FOR YOUR EYES

RIVERBLINDESSPeople naturally want to live near rivers around the world; look at London for instance! In some countries in Africa there is a black fly that also likes living near rivers. But this black fly spreads a parasite with its bite (a parasite is something that can be very small and live in or on people or animals). This tiny parasite can eventually cause the person to become blind when it dies behind the eye and causes a nasty inflammation.River blindness can be prevented by taking a few pills just once a year and Sightsavers works to get these pills to as many people as possible as quickly as possible.

WHEN ARE FLOATERS AN EYE EMERGENCY?

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WHEN ARE FLOATERS AN EYE EMERGENCY?

If you see a shower of floaters and spots, sometimes accompanied by light flashes, you should seek medical attention immediately.

Clumps occur when the vitreous gel begins to liquefy or shrink, usually with aging, and detaches from the retina. For some people, floaters are clumpy; for others, they’re stringy. They may be light or dark. What you see is actually the shadows cast by clumps of vitreous gel when light shines past them onto the retina.

The sudden appearance of these symptoms could mean that the vitreous is pulling away from your retina or that the retina itself is becoming dislodged from the inner back of the eye that contains blood, nutrients and oxygen vital to healthy function. When the retina is torn, vitreous can invade the opening and push out the retina — leading to a detachment.

A study reported in the Journal of the American Medical Association in late 2009 found that sudden presence of eye floaters and flashes means that one in seven people with these symptoms will have a retinal tear or detachment. And up to 50 percent of people with a retinal tear will have a subsequent detachment.

In cases of retinal tear or detachment, action must be taken as soon as possible so that an eye surgeon can reattach the retina and restore function before vision is lost permanently.

Posterior vitreous detachments (PVDs) are far more common than retinal detachments and often are not an emergency even when floaters appear suddenly. But some vitreous detachments also can damage the retina by tugging on it, leading to a tear or detachment.

Light flashes known as photopsia can occur when your retina receives non-visual (mechanical) stimulation, which can happen when it is being tugged, torn or detached.

WHAT CAUSES FLOATERS?

As mentioned in my last blog, posterior vitreous detachments or PVDs are common causes of vitreous floaters. Far less commonly, these symptoms can be associated with retinal tears or detachments that may be linked to PVDs.

But what leads to vitreous detachments in the first place?

As the vitreous gel fills the inside of the back of the eye, it presses against and actually attaches to the retina. Over time, the vitreous becomes more liquefied in the center. This sometimes means that the central, more watery vitreous cannot support the weight of the heavier, more peripheral vitreous gel.

Vitreous gel then collapses into the central, liquefied vitreous. While this occurs, the peripheral vitreous detaches from the inner back of the eye where the retina is located.

Eye floaters resulting from a vitreous detachment are then concentrated in the more liquid vitreous found in the interior center of the eye.

More than half of all people by the time they are 80 will have had a vitreous detachment.* If you are among the 40 percent of people with PVDs who also experience light flashes, then you have about a 15 percent chance of also developing a retinal tear.**

Light flashes during this process mean that traction is being applied to your retina while the PVD takes place. Once the vitreous finally detaches and pressure on the retina is eased, the light flashes should gradually subside.

ITCH! TWITCH! WHICH? WHY?

Why Does My Eye Twitch?

Stress: While we’re all under stress at times, our bodies react in different ways. Eye twitching can be one sign of stress, especially when it is related to vision problems such as eye strain. Reducing the cause of the stress can help make the twitching stop.

 When your eyelid is twitching, you may feel that everyone else can see it, as in this animation that exaggerates the movement. But usually the spasm is so subtle that others wouldn’t even notice.

Tiredness: A lack of sleep, whether because of stress or some other reason, can trigger eyelid spasms. Catching up on your sleep can help.

Eye strain: Vision-related stress can occur if, for instance, you need glasses or a change of glasses. Your eyes may be working too hard, triggering eyelid twitching.

Computer eye strain from overuse of computers, tablets and smartphones is also a very common cause of vision-related stress.

If your eyelid twitching is persistent and very annoying (like the problem experienced by my patient’s wife), you should have an eye exam, because you may need vision correction. If you spend a lot of time on the computer, you also should consider talking to your eye doctor about special computer eyeglasses.

Caffeine and alcohol: Many experts believe that too much caffeine and/or alcohol can trigger eye twitches. If your caffeine (coffee, tea, soda pop, etc.) and/or alcohol intake has increased, cutting back is worth a try.Image

Dry eyes: More than half of the older population experiences dry eyes, due to aging. Dry eyes also are very common for people who use computers, take certain medications (antihistamines, antidepressants, etc.), wear contact lenses and consume caffeine and/or alcohol. If you are tired and under stress, you also may develop dry eye.

It’s best to see your eye doctor for a dry eye evaluation, because many treatments are now available.

Nutritional imbalances: Some reports indicate a lack of certain nutritional substances, such as magnesium, can trigger eyelid spasms. Although these reports lack scientific evidence, I can’t rule this out as a possible cause of eyelid twitching.

If you suspect a nutritional deficiency may be affecting you, however, I suggest talking this over with your family doctor for expert advice rather than randomly buying over-the-counter nutritional products.

Allergies: People with eye allergies can have itching, swelling and watery eyes. When eyes are rubbed, this releases histamine into the lid tissues and the tears. This is significant, because some evidence indicates that histamine can cause eyelid twitching.

To offset this problem, some eye doctors have recommended antihistamine eye drops or tablets to help some eyelid twitches. But remember that antihistamines also can cause dry eyes. It’s best to work with your eye doctor to make sure you’re doing the right thing for your eyes.

Eye Twitching Remedies

In rare cases, some eye twitches just don’t go away. Some of these types of twitches can be successfully treated with Botox injections that help stop muscle contractions. See your eye doctor for proper diagnosis and treatment if the twitching affects half your face or your entire eye, causing the lids to clamp shut.

WHAT CAN YOUR BLURRY VISION MEAN?

MIGRAINE

There are 83 conditions associated with blurred vision and headache. Below are a few of the medical conditions on that list.

Diabetes, type 2
Diabetes can make you feel hungry, tired, or thirsty; you may urinate more than normal and have blurry vision.

Nearsightedness
Nearsightedness is a common eye problem that causes blurry, distant vision.

Tension headache
Tension headaches, caused by muscle tension, are marked by pain, pressure and tightness around the head.

Diabetes, type 1
Diabetes can make you feel hungry, tired, or thirsty; you may urinate more than normal and have blurry vision.

Stroke
A stroke occurs when blood and oxygen to the brain are cut off, and causes numbness, confusion, and more.

Transient ischemic attack (mini-stroke)
Transient ischemic attacks cause headache, numbness, tingling, or weakness in the face, arm, or leg, and more.

Ocular migraine
Ocular migraine usually refers to a type of migraine that can cause temporary blindness in one eye.

Farsightedness (presbyopia)
Presbyopia causes an inability to focus on close objects, and headaches or eyestrain when working or reading.

HEALTHCARE SCAM- PLEASE READ

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SCAM

According to Tracey Thomas, Attorney-Division of Marketing Practices FTC, the Affordable Care Act is in the news lately. And one thing they’ve learned at the Federal Trade Commission is that scams often follow the news. Natural disaster? Charity scams will follow. Implementation of a major new law affecting millions of people? Scammers will be there.

To cut through some of the clutter in the environment with all the articles and discussion of the Act, here’s one key fact to hold onto that can help spot and avoid scams:

You can’t sign up yet.

Enrollment in the new Health Insurance Marketplace doesn’t start until October 1, 2013. Anyone who claims to be able to sign you up sooner is trying to scam you. Please report them.

The FTC has heard from consumers and from other federal agencies that scammers are trying to convince people to act now. Scammers always want to get your money before you have time to stop and think. So remember that date: October 1, 2013. That’s the first time anyone, anywhere can sign up for health insurance through the Health Insurance Marketplace under the Affordable Care Act.

And please: if you see someone trying to enroll people for health insurance under the Act before October 1, 2013, say something. The FTC can only investigate the scams they know about, so every report helps them find and stop the bad guys.