Focus

Lots of us need glasses, but do you know why?

 

If you experience blurry vision, you are probably either nearsighted (can see things up close but things farther away are blurry) or far-sighted (things close are hard to see but further away are in focus). Nearsighted is called myopia, which means the eye is focusing in the front of your retina. Farsighted is called hyperoptic, and that means the eye is focusing behind the retina. Astigmatism means the lens of your eye has an irregular shape, and that's affecting how you see.

                                                      Cones and rods are what allow us to see in color
Did you ever wonder what  the term "20/20 vision" means? It's simpler than you might realize:
The eye chart your eye doctor uses is based on what people with normal vision see at 20' away. Each line has ratings up to 200. Once you've tried reading the chart line for line until you read the smallest line, that's your 'score'... if you can only read the top line, your vision is 20/200 and you would be considered legally blind (without your glasses on of course). If you can read Line 8 of this chart, you have 'perfect' vision.

                                                       An eye chart that might be used to check a child's vision if she can't read letters yet

Your Prescription

The refractive error of the eye can be expressed in numeric terms. The power of the lenses necessary to correct your vision is measured in units called diopters (see below). The first number designates the amount of myopia (minus numbers) or hyperopia (plus numbers). The second number (if present), indicates the amount of astigmatism. The third number shows the axis of the astigmatism. Depending on the sign of the second number, the axis indicates the orientation of the steepest or flattest meridian of the cornea. The fourth number is the "add," or the amount of magnification needed to give clear vision at near. If this number is present, bifocals have been prescribed to correct presbyopia.  -Eye Care Associates of East Texas


                                             And that, my friends, is how they write your glasses prescription. I can read it, but I'm not sure if I get it.

 

What animals have excellent eyesight?

• Birds of prey such as eagles and hawks have 3 to 4 times better vision than humans: They can see a small animal clearly from far away and zoom down to get it with no loss of focus; they can see clearly something at 100 feet what we could see at 20 feet. In human terms, their vision is about 20/4.
• All cats, including large cats such as tigers and leopards
• Dragonflies (consider the size of their eyes)
• Lemurs
• Chameleons

                                          Watch the cat's pupils dilate (enlarge) to let in more light. This is why it sees so much better.

 

Animals with poor eyesight include..

• Rhinos
• Bats
• Bulls
• Deep-sea fish
• Moles

The creature with the largest eyes is the Squid.

Occasionally, people's eyes can't detect colors or see colors differently than most. We say they are color-blind. Red may look green, for example. The reason is the cones and rods in their eyes don't work properly It is in the person's genes (genetic). Here is an explanation of color blindness: https://nei.nih.gov/health/color_blindness/facts_about
How do we know what animals see in terms of colors? Basically, if the animal has eyes without cones, (see above eye diagram) they don't see color. However, some animals see things with some colors. It's explained better here: https://askabiologist.asu.edu/colors-animals-see
Did you know that goats and sheep have horizontal pupils?

Why does the eye doctor put drops in my eyes during an exam?

The eye doctor puts drops in your eyes to dilate the pupils (see cat above) so he or she can see more clearly into your eye. It helps show infections or problems that can't be seen unless the pupil is more open. The reason your eyes are so sensitive to light afterwards is because you're not used to that much light all the time. Your eyes adjust to a dark room by opening up wider, so when you are in bright light with wide-open pupils, the glare is pretty uncomfortable. It helps to wear sunglasses for a while until your pupils shrink back to normal size. https://healthcare.utah.edu/healthfeed/postings/2014/03/030514_moran_eye_dilation.php

If you need glasses to help you see better, your glasses will be made that have a more convex or concave lens. This changes the way light will 'bend' or refract as it enters your eyes, allowing your eyes to work better. Contact lenses serve the same purpose.

 

Did you know Benjamin Franklin invented bifocals in 1784? These glasses have 2 focusing lenses. The lens towards the bottom of the field is for reading, but the rest of the lens is for everything else. There used to be a distinct line in a lens where the bifocal was placed, but now many people prefer a progressive lens which does a more gradual change in focus. Bifocals are helpful as eyes age, but can be used at any age. When people first adjust to bifocals you may notice they tilt their heads up as they try to look through the lower lens. 

Originally, there were actually two separate lenses held in the frame with a piece of metal between them. Not ideal, but very helpful at the time. Now the lens is ground as one piece.


Good source of info about eyes and eye problems here: https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/eyes-common-problems
Some people choose to have lasik surgery to correct their vision. Here's an explanation of what happens in lasik surgery: https://www.mayoclinic.org/tests-procedures/lasik-eye-surgery/in-depth/lasik-surgery/ART-20045751

Sometimes when you get your driver's license renewed, you may be asked if you see lights flashing on either side of a screen. This is to check your peripheral vision--what you can see out of  'the corner of your eye.'

 

Cataracts are a cloudy film that occurs in the eye, making it harder and harder to see. In the past, the person would simply lose vision due to cataracts, which are fairly common with age. Now, eye surgeons can surgically remove the cloudy cornea and replace it with a permanent lens called an 'interocular lens,' restoring the person to vision that is often better than ever before, because it's also correcting the shape of the cornea. Usually people only need generic reading glasses after cataract surgery, which can be purchased at a drug store with no prescription and at a low cost.

 

Here's a video that explains cataract surgery: http://david-richardson-md.com/cataracts/what-is-cataract-surgery/

 

What are careers in vision care?

-an Ophthalmologist is a trained medical doctor who specializes in diseases of the eye and does surgery on the eyes. They have completed a full medical program including 4 years of college, 4 years of medical school, and another 4 to 5 years of specialty training.

-an Optometrist holds a Bachelors Degree (4 year degree) and can diagnose problems with the eyes. They generally refer more difficult cases to an Ophthalmologist, but in some states are allowed to do surgery on the eyes.

-an Optician is trained to create and fit glasses and contact lenses on patients. They typically study to receive a two-year degree, and sometimes it is a one-year program. Opticians may work in a lab making glasses, or may work with patients in selecting and fitting their glasses.

Here's a video of how the lenses of your eyeglasses are made: https://www.bing.com/videos/search?q=how+are+eyeglasses+made&&view=detail&mid=1149977C73E5B2BC7CFE1149977C73E5B2BC7CFE&&FORM=VRDGAR

Have your eyes checked once a year. That way any problems can be caught early and treated.