The Dangers caused by wearing glasses with incorrect Prescription.

By Dr.Loft ,O.D.

Public, 21 October 2023

 

Introduction

First of all, if you are not Thai people, and you are not living in a developing country like Thailand, you need to understand the general situation in this country first.

 

In Thailand, there are no laws regulating the standards of practice of those involved in the care of patients' vision health. There are no laws regulating who has the ability to test the vision of people in Thailand. No matter who you are, how much knowledge you have, and if you want to be a glasses store owner, you can open a business to sell glasses without the law prohibiting you from doing so. Therefore, you can do it easily without feeling guilty about whether what you are doing is right or wrong.

 

And currently, although there have been optometrists in the country for over 20 years, the old glasses store capital system has refused to allow the law to come out to control the standards of practice of those involved. This lack of regulation leads to a wide range of standards, from good to poor. Some patients may be lucky enough to receive the correct care, but many are not. So vision care system has led to a situation where there is no guarantee of quality care.That's the charm of Thailand ,the land of funny.

 

This story happened while I went to send a letter and saw a glasses booth in a tent in front of the post office. The optician was busy measuring refraction and sell the glasses for customers by trying trial different lenses in the middle of the sun at noon, which was about 42 degrees Celsius. The distance of the chart used to test visual acuity was probably 2.5 meters, with the question "Is it clear? Which one is clearer, this one or this one? Which one is clearer?" going on and on.

 

Meanwhile, another person was picking up lenses from the stock and polishing them next to the person who was measuring the customer's vision, for the customer who had their vision measured 10 minutes ago. The entire process, from measuring the vision to receiving the glasses, took less than 30 minutes.

 

I suddenly thought, "He's good, isn't he?" How can he make glasses in a tent in the hot sun and have customers wait for them in half an hour? (Courageously) Then I asked myself, "Am I brave and crazy enough to do something like this? If not, where does the courage of these person doing it come from?”

 

At the same time, I got the answer in my mind, "Because he doesn't know what terrible damage will happen to his customers from dispensing inaccurate prescription or inaccurate center of lenses. Because he has the self-comforting excuse that “they can wear it, it's clearer now, right?”

 

This story is like "a child is not afraid of a  electrical power outlet because he has never been electrocuted.”

 

The Problem

This story may make people who work without standards work harder, but I have to do it. Because if we don't start right now, the standard of service will not be established. The public will not learn which right or wrong, and there will be patients with illnesses that need to be treated urgently. But with an environment (no legal protection)  that is not conducive to awareness, they will not care. In the end, it leads to vision loss. And now I think it's time to work together to create a new system for eye care services.

 

Misconceptions (caused by ignorance)

 

Most people often misunderstand that making a pair of glasses to use is just to make Vision clearer than before or better visual acuity . But the truth is that "being sharp alone doesn't tell us anything more than just being sharp and readable, but it doesn't mean that seeing sharp means that the vision we are wearing is the correct vision.”

 

For example, if a young child (who has very good accommodation) has a real myopia of -1.00D. But if we try to put -1.25, -1.50, -1.75, -2.00, ..., -6.00D, this child will be able to see the standard-sized letters that normal people can see clearly, which is 20/20 at a distance of 6 meters. It is as sharp as wearing a vision of -1.00D, and there is a tendency that the more minus lens you put in trial, the sharper patient will say, even if it is the wrong value.

 

Another example, suppose the child has a true refractive error +3.00 D, even if you don't correct the child's vision, they can read 20/20 or more. Or we trail prescription by +1.00, +1.25, +2.00, +2.50, or +3.00D, the child can also read VA 20/20 with all lens even in minus power.

From the two examples above, any value prescribe, the child can see clearly, read VA-chart in the 20/20 row correctly according to the standard. Then how do we know or is there any tool to confirm which value is the child's real prescription?

 

Which can be summarized as "glasses that are clear and read VA 20/20 does not mean that the glasses you wear are always the correct value." But it just can only be said that "it is clear to wear" ,that’s it.

 

Therefore, in clinical optometry, the vision test cannot rely on just one system of examination. But there must be many confirmation tests to confirm that the vision we have tested is the correct correction. Examples of confirmation tests will be discussed at the end of the article.

 

What I am try to say is , there are lack of standards in eye care services in Thailand. I believes that many people misunderstand that making glasses that are clear to see is enough. However, this is not the case. There are many factors that can affect vision, and it is important to use a variety of tests to confirm the correct vision. So I provides two examples to illustrate my point. In the first example, a young child with a true myopia of -1.00D can see clearly with lenses ranging from -1.25D to -3.00D. This is because the child's lens accommodation can compensate for the additional minus power. In the second example, a child with a true Hyperopia of +3.00D can also see clearly with lenses ranging from +1.00D to +3.00D. This is because the child's eyes are still developing and can accommodate to the additional plus power.

 

Back to our story

 

Therefore, the word "clear" alone is not enough to tell us whether the vision we are using is the correct value or not. Humans have the ability to adapt as a capital. We will endure until we finally tolerate the condition. We can live, but the visual system being forced to get used to the wrong vision will cause problems with the cooperation of the two eyes, lens problems, and focusing problems. Today, I will talk about the impact of using vision values that are not suitable for patients. What problems will it cause?

 

Who is called ... has uncorrected vision?

 

People with uncorrected vision or Uncorrected Refractive Error mean "those who have vision problems such as nearsightedness, farsightedness, astigmatism, and have not been corrected by wearing glasses, contact lenses, or LASIK to solve the problem. Including those who already have glasses  but refuse to wear them, or wear glasses regularly but the prescription is incorrect" All of these are considered to be in the Uncorrected Refractive Error group.

 

Ask yourself...Why do we correct vision?

 

The purpose of resolving vision problems is to "make vision clear and make the cooperation of our binocular system work like normal people. "People with normal vision (Emmetropia) mean that "they can see distant images clearly VA 20/20 at 6 meters with out compensate by accommodation system or relaxed accommodation." (Keyword is that distant images are clear but the lens must be relaxed. If it is clear but not relaxed, it is considered abnormal.)

 

And when people with normal vision see distant images clearly without compensation of focusing system because of all light rays combined to focal point and focus on retinal centralist neutrally, when reading a book, the lens must have to accommodate appropriate power in each reading distance.

 

For example, if reading close at 40 cm, the lens must accommodate +2.50D. If it is more ,it is considered abnormal but may be a little bit less than stimulus because of depth of focus effect. And the eye muscles must be at an appropriate angle, have good muscle strength, and have no hidden strabismus.

 

But the working of the lens and eye muscles that work correctly can only happen if there is no vision problem or if it has been corrected correctly. All functions will be able to work correctly and in harmony. If the vision is abnormal and not corrected, it will also cause the system to be imbalanced.

 

Therefore, accurate vision measurement is the first step in resolving other vision problems. By correcting vision to normal, the lens and eye muscles will learn to work together normally and perfectly , and the system will improve naturally. Vision measurement is not just "measure only clearly" without considering how clear it will affect other functions. Have you ever been clear but had a headache, clear but couldn't wear it, clear but sore eyes, pain in the eye socket, pain in the temples, pain in the back of the head, pain in the neck? That's it.

 

Conclusion in this point

 

The purpose of vision correction is to make vision clear and make the cooperation of the binocular system work like normal people. This can be achieved by accurate vision measurement and the use of appropriate corrective lenses or contact lenses.

I emphasize the importance of accurate vision measurement in order to achieve the desired results. I also warns against the dangers of wearing incorrect glasses or contact lenses, which can lead to a variety of problems, including headaches, eye strain, and even vision loss.

 

“Comprehensive eye exam is not just eyeglass measurement”

 

I and my friend in optometry do not like to be called optometry role like "eyeglass measurers- wat wan in thai word” because our work is not just easy as eyeglass measuring. I would like to ask technicians or doctors in hospitals to understand the role of optometrists. They studied for 6 years, not to learn just "eyeglass measuring" as you all misunderstood.

 

"Glasses" or "eyeglasses" are objects with a constant power at each point. We can take our glasses to measure the value in the lens with a lensometer. If the lensometer is standardized, no matter how many times we measure, we will always get the same value because glasses are inanimate objects. The value obtained from measuring glasses is constant.

 

However, comprehensive eye exam is working with humans. There are issues of age, education, emotions, knowledge, understanding, awareness, and cooperation, which are subjective. All of these affect the examination.

 

And we are playing with a system that can change all the time. Therefore, it requires a lot of skills from the examiner and requires many confirmation tests to confirm that the measured vision value is correct.

 

Therefore, comprehensive eye exam is different from eyeglass measurement. And that is why computer vision measurement machines can be used sometimes, but not always. For children, it is not possible at all. The younger the child, the higher the error rate. To the extent that the reliability is below 50% in children under the age of 6. And the same patient, measured vision on the same day, with the same machine, measured 10 times, got 10 refraction values. If you change the measuring machine, it will be even worse.

 

This is clear that if you want to use a computer to measure the power of lenses from glasses, it can be measured by lensometer. But if you use a computer to measure human eyes, it can be measured, but it is not reliable.

 

Explanation the point

 

I’m an optometrist who is concerned about the misunderstanding of the role of optometrists. I argue that eye exam is not the same as eyeglass measurement. Eye exam is a more complex process that requires the skills and expertise of an optometrist.

 

glasses are inanimate objects with a constant power at each point. Therefore, they can be easily measured with a lensometer. However, human eyes are not inanimate objects. They are constantly changing, and they are affected by a variety of factors, such as age, education, emotions, knowledge, understanding, awareness, and cooperation.

 

computer vision measurement machines (Auto-refractometer are not always accurate, especially for children. This is because children's eyes are still developing, and they may not be able to cooperate with the machine.

 

Conclude that eye exam is a complex process that requires the skills and expertise of an optometrist. people should seek the help of an optometrist for accurate vision measurement.

 

Visual perception of people with normal and abnormal vision

 

People with normal vision (Emmetropia)

 

When looking far away, Light travels from infinity (light from infinity is plane light). When it passes through the cornea, lens, and vitreous, it must focus on the retina exactly to create a sharp retinal image while the lens is in a relaxed state (Relax Accommodation).

 

When looking close,The light that hits an object at a close distance and then enters the eye will be divergent rays. Therefore, when the object moves closer, the focal point will move behind the retina. This causes a blurry image on the retina. This retinal blur will stimulate the lens to bulge up, which we call the "lens focusing system" or medically called accommodation.

 

Therefore, the distance of the object will trigger the response of the lens. For example, an object at a distance of 40 cm will stimulate the lens to work +2.50 D (obtained from the equation F = 1/f, where F is in diopters, f is the focal length in meters). And the lens working +2.50 D will stimulate the Medial Rectus muscle to converge by 15 prism diopters (7.5 prism diopters per eye) (estimated value from a person with PD 64).

 

We can measure the relationship between the lens and the muscles by finding the AC/A ratio. This will tell us that when the lens works 1.00 D, it will change the muscle function (convergence/divergence) by how many prism diopters from the original. The standard value is AC/A = 4:1, which means that when the lens works 1.00 D, it will make the muscles work convergence for 4 prisms.

 

summary point

 

In people with normal vision, the light from objects at all distances is focused on the retina. This is because the cornea, lens, and vitreous have the correct shape and power to bend the light to the correct point.

 

When looking far away, the light from objects is parallel, so the lens does not need to change shape to focus the light. The lens is in a relaxed state, and the muscles that control the eye alignment are also relaxed.

When looking close, the light from objects is divergent, so the lens must bulge up to focus the light. This is called accommodation. The muscles that control the eye alignment also need to work to bring the eyes together to focus on the close object.

 

The AC/A ratio is a measure of the relationship between the lens and the muscles. It tells us how much the muscles need to work when the lens changes shape. A higher AC/A ratio means that the muscles need to work more when the lens changes shape.

 

 

People with abnormal vision

 

People with abnormal vision have difficulty focusing the light on the retina. This can be caused by a variety of factors, including:

• Myopia (nearsightedness): The cornea and lens are too powerful, so the light is focused in front of the retina when looking far away.
• Hyperopia (farsightedness): The cornea and lens are not powerful enough, so the light is focused behind the retina when looking far away.
• Astigmatism: The cornea or lens is not perfectly round, so the light is focused at different points on the retina.
• Presbyopia: The lens loses its flexibility so it lost ability to change shape, so it is difficult to focus on close objects.

People with abnormal vision may need to wear glasses or contact lenses to correct their vision.

 

Visual perception of people with abnormal vision

 

People with nearsightedness (Myopia)

 

When looking far away ,the light that travels from infinity through the optical system is focused in front of the retina, which causes a blurry image. The lens chooses to relax (because accommodation will only make the image blurrier in this cases). Therefore, people with nearsightedness will definitely see far away blurry.

 

When looking close, people with nearsightedness can usually see clearly at close range (but how far they can see depends on how nearsighted they are). This is because the light from objects that are close will cause the focal point (which was originally in front of the retina) to move back until it lands on the retina and produces a sharp retinal image while the lens is still in a relaxed accommodation state.

 

Problems with uncorrected nearsightedness

 

It can be seen that people with nearsightedness have less chance of using the accommodation system, the shorter the nearsightedness, the less it is used. And this is the root cause of the problem of the focus system working too little (Under Accommodation).

 

As a result, the focus system does not work and one of the natural properties of the organ is that "things that have never been used will naturally deteriorate." This results in a malfunction of the lens (Accommodative Insufficiency) and also affects the functioning of the eye muscles.

 

For example, normally, when reading a book at 40 cm, the lens will work +2.50 D. The eye muscles will force the eye muscles to converge 15 prisms. But patients with nearsightedness who do not wear glasses to read, for example, -2.25, will see clearly at 40 cm without accommodating, while the eye muscles still have to work to get 15 prisms the same. This condition also makes the AC/A ratio work abnormally. When left alone, it will become High Exophoria and Convergence Insufficiency will follow.

 

Summary point

 

People with nearsightedness have corneas and lenses that are too powerful, so the light is focused in front of the retina when looking far away. This causes a blurry image.

 

To see clearly at a distance, people with nearsightedness can not use their accommodation system to focus the light on the retina case of accommodation is Plus power system, mean more accommodate more blur in this case. But they can see clearly with out glasses at near without or small accommodation. But to do that it can also lead to problems with the accommodation system, such as accommodative insufficiency.

 

Accommodative insufficiency is a condition in which the accommodation system does not work properly. This can lead to blurry vision at near, headaches, and eye strain.

 

People with nearsightedness also have a higher risk of developing convergence insufficiency. Convergence insufficiency is a condition in which the eye muscles do not work together properly to focus on close objects. This can lead to double vision, headaches, and eye strain, too.

 

Wearing glasses or contact lenses can help people with nearsightedness see clearly at all distances. This can help to prevent problems with the accommodation system and convergence insufficiency.

 

Additional information about Nearsightedness

Untreated nearsightedness can lead to a number of problems, including:

• Eye strain
• Headaches
• Double vision
• Reduced depth perception
• Increased risk of eye diseases

Early treatment of nearsightedness can help to prevent these problems.

 

People with farsightedness (Hyperopia)

 

Farsightedness is a vision disorder that is still misunderstood by many thai people case of thai word call “long sight-สายตายาว” so the confuse between hyperopia and presbyopia because of the sign and symptom look like. They understand that "farsightedness only occurs in the elderly." This is not entirely true because all young children are born with farsightedness and the farsightedness will gradually decrease as the eyeball lengthens when they grow up. It will become normal vision when they are 8-9 years old. Some people may become nearsighted, while others may still have farsightedness. Because of this misunderstood case many optician still believe that children will have problem only with myopia and astigmatism ,but not hyperopia. Cause many hyperope children when they have problem and go to optical shop will get minus lens.

 

When looking far away,the light travels from infinity through the optical system and focuses behind the retina, which causes a blurry image on the retina. This causes the lens to be stimulated to work and accommodate to pull the focal point onto the retina.

 

People with farsightedness who still have good focusing power do not have clear vision problems because the lens works for them. However, people with very high farsightedness often have problems with headaches or eye misalignment (esotropia) due to the lens having to work too hard. This is common in children or latent eye misalignment (esophoria).

 

When looking close , When reading (objects are close), the focal point will be further away, so the lens has to work harder (over-accommodate). This is the reason why people with farsightedness often get headaches when they have to read or look close. Currently, many patients with unexplained headaches have problems with esophoria caused by the lens being overstimulated.

 

People with farsightedness will have problems when looking at both far and near distances. The lens will be stimulated all the time, which will cause the lens to have to work too hard to focus (over-accommodate).

 

For example, a person with farsightedness of +3.00 D must accommodate +3.00 D to see clearly when looking far away. When reading a book at 40 cm, the lens must work an additional +2.50 D for a total of +5.50 D to read at 40 cm (while people with no farsightedness problems only need to work +2.50 D).

 

Problems in patients with untreated farsightedness

 

The overworking lens will cause the convergence muscles to work more than necessary (more than 15 prisms), which can cause double vision. This is especially common in patients with esophoria and a high AC/A ratio. But brain does not want to see double vision, so the eye muscles must exert force to pull the eyes back (negative fusional vergence) to merge the images into one,fusion.

 

This causes both the lens and the eye muscles to work very hard, which is the cause of headaches, migraines, drowsiness, eye fatigue, blurred vision when looking close, blurry or melting letters, blurred vision after reading for a long time, and focusing problems when changing the viewing distance. The eyes may also be red and bruised.

 

Explanation point

 

People with farsightedness have corneas and lenses that are not powerful enough, so the light focuses behind the retina when looking far away. This causes a blurry image.

 

To see clearly at a distance, people with farsightedness need to use their accommodation system to focus the light on the retina. This can be tiring, and it can also lead to problems with the accommodation system, such as over-accommodation.

 

Over-accommodation is a condition in which the lens works too hard to focus the light on the retina. This can lead to blurry vision at near, headaches, and eye strain.

People with farsightedness also have a higher risk of developing divergence insufficiency. Divergence insufficiency is a condition in which the eye muscles do not have enough strength muscle to pull out  to combine to image of two eye in single fusion vision. This can lead to double vision, headaches, and eye strain.

Wearing glasses or contact lenses can help people with farsightedness see clearly at all distances. This can help to prevent problems with the accommodation system and vergence insufficiency.

 

Additional information

farsightedness can lead to a number of problems, including:

• Headaches
• Migraines
• Drowsiness
• Eye fatigue
• Blurred vision when looking close
• Blurry or melting letters
• Blurred vision after reading for a long time
• Focusing problems when changing the viewing distance
• Red and bruised eyes

Early treatment of farsightedness can help to prevent these problems.

 

Negative effects of uncorrected vision

1. Over/Under-Accommodation

 

Uncorrected vision can cause the lens to work too hard or too little, which can affect the abnormal collaboration of the lens and eye muscles (Accommodative convergence/Accommodation system).

 

Understanding the collaboration of the lens and eye muscles, The lens (Crystalline Lens) and eye muscles (Ocular Muscle) work together automatically. For example, when we look at an object that is getting closer, the lens will adjust the focus to be clear. At the same time, the eye muscles will automatically converge. We call the lens focusing system Accommodation System and the process of convergence of the eyeballs Convergence System.

 

When these two systems work together, we call it Accommodative Convergence System. The value that connects the two systems is AC/A ratio. Both systems will always work together because they use the same cranial nerve 3 (Oculomotor) to work together to achieve clear single and binocular vision.

 

Binocular vision is a system that occurs in predators such as tigers, lions, humans, dogs, cats, eagles, and owls. Notice that their eyes are both located in the front of the skull.

 

Because the eyes are located in front, it creates a binocular vision system. This allows the images to be seen in depth (Depth Perception) and 3D. This makes it easier to catch prey. Unlike herbivores such as elephants, horses, cows, buffaloes, rabbits, zebras, giraffes, frogs etc. whose eyes are located on the sides. These animals do not have Depth Perception, but their side eyes help them to be aware of predators around them.

 

Humans do not have binocular vision at birth, but learn to use both eyes together. This system develops during the first 2-3 months after birth to allow for better synchronization and refinement.

 

However, if something interferes with this development, such as severe vision problems or blindness from congenital cataracts, it can disrupt the development of binocular vision. This can lead to strabismus (eye misalignment) in children, and if left untreated, amblyopia (lazy eye) can develop.

 

Therefore, the collaboration of these two systems has an appropriate proportion. This relationship is called the AC/A ratio, or Accommodative Convergence/Accommodation. In nature, the AC/A ratio is 4:1. ,To learn more about AC/A ratio, visit the link:http://www.loftoptometry.com/AC:A_ratio.

 

2. Uncorrected vision problems cause imbalance of the images from the two eyes (Binocular Imbalance)

 

The world we see is a single image, but that single image is made up of two images from two eyes. This means that the single image we see is actually the result of the brain combining the image signals from each eye into a single image and seeing it in 3D. This is caused by the cooperative working of the two eyes, also known as Binocular vision.

 

For the brain to combine the images into a single image and have good binocular vision, the images from each eye must be equally sharp and the lens and eye muscles must work equally. This makes image fusion easier and produces high-quality images. This will only happen if the person has no vision problems or has had their vision problems corrected.

 

If there is any abnormality in one eye, such as a large difference in vision that has not been corrected, the brain will choose the image from the better eye and suppress the signal from the worse eye. This makes the worse eye never have the opportunity to send signals to the brain because the brain does not accept it. This eventually leads to amblyopia.

 

Therefore, the correct way to solve vision problems is to correct the distance vision so that they are equally sharp and the lens works equally. This is called Binocular Balancing to prevent one eye from being sharper than the other. And if the binocular balance is not measured well, it will also cause Accommodation to be unbalanced. Image fusion will be difficult, and if the imbalance is too great, the brain may choose to suppress the signal from one eye and cause it to become amblyopia.

 

3. Makes vision problems worse

 

"People with myopia who do not correct their myopia will become more myopic."

This research is contrary to the general public's belief that wearing glasses will cause myopia to increase, or that when making glasses, they reduce the prescription for weak numbers, believing that it will slow down myopia. These beliefs are completely wrong and the research confirms that "people with myopia who do not accept correction will become more myopic.”

 

Therefore, if the glasses you are wearing are starting to become blurry, don't be complacent, don't insist on using them, because it will cause lens problems and eye muscle problems. Adapting to glasses slightly (1-2 days) is normal. But if you have to adjust for 5 days or more and still can't adjust, don't insist because the right glasses really don't need to be adjusted and if you try to adjust to the wrong glasses, it will create a disaster.

 

4. Causes latent strabismus (High Phoria)

 

For example, uncorrected hyperopia often causes latent inward strabismus (esophoria), especially when looking close, or people with uncorrected myopia will cause High Exophoria. This causes problems with using vision, such as headaches, pain in the eye sockets, headaches in the nape of the neck, can't read books for a long time, and it's very difficult to focus.

 

Therefore, if you have vision problems, you should not be complacent. It will have many consequences and should be corrected correctly. Because the wrong eyeglasses are no different from uncorrected vision problems, which cause various problems. In the meantime, if there are problems with the lens and eye muscles, it may be caused by vision problems that have not been corrected. And if corrected correctly, the system balance will return to normal again.

 

Varify Correction 

 

1.NRA

NRA, or Negative Relative of Accommodation, is a test that can be used to assess whether the distance vision we prescribed is an exaggerated myopia, or over minus.

The main principle of NRA is to have the patient look at a 20/25 letter at a distance of 40 cm to stimulate the lens to focus at +2.50D to see clearly. Then, we will gradually increase the positive value, +0.25D at a time, to relax the lens. So if there is no positive lens to help, the patient will be focusing at +2.50D. So if we put the positive lens, the patient should be blurry when we increase the positive lens to +2.50D. However, if it exceeds this, it indicates that the distance vision we prescribed is over minus or under plus value.

 

In addition, we can also assess the strength of the eye muscles to converge, which is positive fusional convergence. It can be remembered that if NRA > +2.50 D, the distance vision may be over minus/under plus. But if NRA < +1.50, it indicates that the ability to converge is low.

 

2.BI-reserve (Negative fusional vergence reserve test)

 

BI-reserve, or a test to see the ability of the eye muscles to diverge (Divergence), or it can also be called Negative Fusional Vergence.

 

But at the same time, we can use this value to assess whether the distance vision we prescribed is over minus/under plus.

 

Normally, in BI-reserve or BO-reserve, it is a test to see the power of the force to combine images of ocular muscle. There are two systems involved in this, which are accommodative convergence and fusional vergence. Fusional vergence also has both positive vergence and negative vergence.

 

When there are both forces, so during the test, we have to ask the patient to report when they see blurry, when the image separates, and when the image comes back together.

 

The blurry image indicates that the accommodative convergence force is starting to run out, then it will be the fusional vergence force that works until it can't take it anymore, the patient will see that the image separates. As for the image coming back together again, it is the sensitivity of the fusional vergence system to run to catch the image to come together again.

 

Therefore, if we measure the distance vision correctly, the patient should be able to read the 20/20 row with accommodation in a relaxed state. So when we do BI reserve, the patient will only have the negative fusional vergence force alone, without the accommodative convergence force to help. So the patient should see the image split into two without seeing it as blurry first.

 

However, if it is found that the patient sees blur as well, it indicates that the prescribed vision has an over myopia or there is still undercorrected hypyeropia. This is due to the involvement of accommodative convergence and is a sign that the distance vision is still an over minus value.

 

Summary point

NRA and BI-reserve are two tests that can be used to assess the binocular vision system.

 

NRA is a test of the ability of the eye muscles to converge. A high NRA value indicates that the eye muscles are strong and can converge easily. This is important for binocular vision, as it allows the eyes to focus on objects that are close together.

 

BI-reserve is a test of the ability of the eye muscles to diverge. A high BI-reserve value indicates that the eye muscles are strong and can diverge easily. This is also important for binocular vision, as it allows the eyes to focus on objects that are far apart.

 

Another way NRA-test can be used to assess whether the distance vision that has been prescribed is correct. If the NRA value is too high, it suggests that the distance vision is over minus, meaning that the patient has less myopia than was originally thought. This can lead to problems with binocular vision, such as double vision or headaches.

 

3.Binocular Cross Cylinder (BCC)

BCC, or Binocular Cross Cylinder, is a test that is used to measure the amount of appropriate addition value of both eyes to prescribe for reading 40 cm ,but you can test monocularly to check balancing of of accommodation balancing. Another words used to measure the weakness of accommodation system meaning of BCC is Zero ,meaning that the patient do not need addition for reading but if BCC is plus, meaning that the patient need that plus add to help for reading, More plus BCC mean more plus addition you have to prescribe.

 

But this is not a point , the point is if BCC is too higher than norm, yes it could be, but  it’s sign of over minus or under plus correction.

 

For Example

 

A 30-year-old patient with a true myopia of -1.00D ,but BCC value of +1.50D (norm value of 45 year old). This is may because the patient's lens accommodation have to use some of accommodation to compensate over minus correction ,so sign of lag of accommodation will shown . And you have a duty to verify it especially in young patient with high plus BCC.

 

4.Retinoscopy

Retinoscopy is a test that uses a device called a retinoscope to measure the refractive error of the eye. The retinoscope projects a beam of light into the eye, and the examiner looks for the nutral reflex of the light on the retina. The amount of sphere and astigmatism power can be determined by the shape of the reflex.

 

Conclusion

 

Uncorrected or improperly corrected vision can not only cause blurred vision, but it can also disrupt the functioning of the eye's binocular system.

 

The correct refractive error is not just about being able to read 20/20. It is also about being able to see clearly at a distance without the lens having to strain. Wearing glasses with the wrong refractive error can disrupt the function of the eye muscles and lens function, which can lead to problems with binocular vision.

 

It is important to have a comprehensive eye exam by an optometrist to ensure that you are receiving the correct refractive error. This exam should include a variety of tests, including:

• Refraction to measure the refractive error of each eye
• Visual acuity testing to measure the sharpness of vision
• Ocular motility testing to assess the movement of the eyes
• Binocular vision testing to assess the ability of the eyes to work together

By taking the time to have a comprehensive eye exam, you can help to ensure that you are seeing your best.

 

Closing thoughts

I hope that this article will raise awareness of the importance of eye care. Consumers should not buy ready-made glasses, but should instead see a professional to get an accurate diagnosis and treatment. Providers who measure vision should be aware of the risks associated with inaccurate prescriptions.

 

Hope this article will give some idea or some benefit to you ,thank for your reading.

 

Dr.Loft ,O.D.

 

Loft Optometry 

578 Wacharapol rd , Tharang ,Bangkhen ,BKK ,10220 

moble : 0905536554

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