Tag : myopia

HomePosts Tagged "myopia"

What does my glasses prescription mean anyway?

This is probably one of the most common questions I get.  Even though my husband and I are ophthalmologists (eye surgeons), we still do a large number of glasses and contact lens prescriptions.

Here’s my son, Taj performing his first refraction with the phoropter when he was 1.5 years old. This picture was taken at the Children’s Discovery Center, our equipment in our office is much newer than this!

[caption id="attachment_1179" align="aligncenter" width="695"] Taj adjusting the phoropter[/caption]

Refraction is the term used to describe that process of fine tuning your glasses prescription when you sit behind the phoropter. Everyone gets so nervous when we ask “Better 1 or 2”.  They don’t want to get the answer wrong.  And, the thing is there is no wrong answer.  Your glasses prescription is individualized to suit your needs.  And, most optical shops (like ours) can always redo the lenses for free for three months if you end up getting the glasses and they just don’t seem to work for you, even after giving them a couple weeks.  So, that should take the pressure off.

So, you did it – finished the dreaded “1 or 2” test and your doctor hands you a prescription.  It’s like an ancient language – what does it all mean??? OD, OS, Sphere, Cylinder, Axis, Add??

 

OD and OS

First, OD and OS.  OD stands for oculus dextrous, for those of you who took Latin in high school, which means right eye.  OS stands for oculus sinister, for left eye and OU stands for oculus unitas or both eyes

 

Sphere (Sph)

This refers to the spherical lens necessary to sharpen your vision to 20/20 (if possible for you).  The number is the amount, measured in diopters, needed to correct nearsightedness or farsightedness.  In this example, this patient has a minus in front of the number because he is myopic or nearsighted.  This patient can see near, but not far. Whether the number is plus or minus, the higher the number, the stronger the prescription.

This patient’s eye is a little longer than normal, so the light focuses in front of the retina instead of on it.

Myopic eye diagram

 

A minus spherical lens, or a concave lens, helps focus it onto the retina.

Screen Shot 2015-03-17 at 12.56.21 PM

Here’s another prescription with a plus number in the sphere column, meaning this patient is hyperopic, or farsighted.  That means this person can see far away, but not up close (that’s only for adults).  Though, that’s not entirely accurate – most kids are hyperopic.  As their eyeball elongates, they outgrow this farsightedness – but, their vision is never affected by it because their eye is so flexible it’s able to focus past the farsightedness, giving them 20/20 vision.

This patient is a child and her eye is a little shorter than is normal, so light comes to focus behind the retina.

Screen Shot 2015-03-17 at 12.56.27 PM

A plus spherical lens, or convex lens, helps focus the light onto the retina.

Screen Shot 2015-03-17 at 12.56.44 PM

Cylinder (Cyl)

There are two types of lenses in glasses prescriptions – sphere and cylinder.  Cylindrical lenses are used for correcting astigmatism.  Sometimes new patients come to me and say, “I have…..ASTIGMATISM” (que the scary music).  It’s almost as if it’s a terrible disease (which it’s not).  Astigmatism just means the front of your eye, or the cornea, is shaped more like an egg or football, instead of being perfectly spherical like a ball.

Most people have some astigmatism.  For people with astigmatism, it means that images are slightly stretched horizontally or vertically, like a fun house mirror.  This number can be minus or plus, but practices tend to stick to one sign.  In our office, all our prescriptions are written using minus cylinder.  If you don’t have a number in this column, it means you don’t have any astigmatism.

Axis

Axis refers to the direction or position in which the cylindrical lens is pointed to correct the astigmatism.  It’s measured in degrees.  If your prescription doesn’t have a cylinder number, then it won’t have an axis number either.  Remember high school geometry?  That’s what the axis refers to, just like your old protractor.  Do they still use protractors in high school?  Probably not, I bet there’s some app for that now.

cyl axis

Add

This number is also measured in Diopters and refers to the extra magnifying power needed to help you see up close if you are presbyopic.  Presbyopia is the condition which affects most individuals over the age of 40.  You probably know the signs if you fall into this age group – reading, using your phone, all starts to get a little harder and you have to hold things far away for them to be clear.  That’ presbyopia. If you wear bifocals or progressive glasses, then there will be a number in this column.  Add power is always a plus number and it can range from as low as +0.75 to +4.00 (in rare cases), though the normal add powers are between +1.25-+3.00.

Prism

My patients will have a number in this column.  This is for correcting eye misalignments (strabismus) and reducing double vision.  Depending upon the type of strabismus (eye drift up, out, in or down), the prism will be oriented in different directions to counter the eye misalignment.  Most people do not need prism in their glasses.

And, we’ll close with my favorite pic from the Cat in the Hat – it’s actually very accurate!

How can I prevent my child's glasses from getting stronger?

Why do my child’s glasses keep getting stronger? This is one of the most common questions I encounter in my practice.  I see a patient after they have failed their vision screening exam at their pediatrician’s office and diagnose them with nearsightedness.  The following year, their myopia is worse and the glasses prescription has to be increased.  The year after, same thing happens.  I always reassure parents,”‘This is normal.  Expect the prescription to increase every year until they hit college age”.  But, of course, as a parent, it’s worrisome.   Parents always ask me about TV/video games/foods they can eat, anything that could help “strengthen” their children’s eyes.  Before, I would have to tell them that nothing could be done, it was just genetics.  But, not so anymore!

But, first, let’s just review what is myopia?  Myopia is what most people often call nearsightedness  – you can see up close, but not far away.

 

Myopia is the most common refractive error in kids, and it’s on the rise. My son is obsessed with asking if my husband is nearsighted or farsighted after we read this page in the Cat in the Hat book at bedtime.

 

For myopes, the light rays from the outside world are focused just in front of the retina.  It can be because the eye is a little longer than usual (axial myopia), sometimes for adults, it’s because there is a cataract refracting the light differently.  But, let’s stick to the kids for this discussion.

Myopic eye diagram

So, it makes sense if one parent is myopic, then the child has a good chance of becoming myopic as well.  Eye size is inherited just as hair color, height, etc.  My boys don’t wear glasses for real (though they are modeling them in the picture above), but I should qualify this as a YET.  I am not nearsighted, nor is anyone in my immediate family, however, my husband’s side is a different story.  So, there certainly is a good chance that they may require glasses in the future.

Now, here’s a little throwback to high school physics.  For nearsighted individuals, the lens shape (concave) helps to focus the light on to the retina.

Screen Shot 2015-03-17 at 12.56.21 PM

Now, to the good stuff?  What can be done?  Two new studies have come out which have had some very promising results in terms of decreasing the progression of nearsightedness in kids.

1.  Increase Time Outdoors

One study examined 2000 children in Australia and specifically looked at the type of activities children were doing.  They then followed-up the kids 5- 6 years later to figure out which activities seemed to make a child more nearsighted.

  • Time spent indoors
  • Time spent doing near work (reading, homework, iphone, etc).
  • Family history of nearsightedness

So, what does this mean.  Being outdoors in the sunlight, is protective.  Kids who spent 1-2 hours/day outdoors, were on average a whole diopter less nearsighted than their peers who did not.  That would mean -3.00 prescription instead of a -4.00 prescription. And, the more time kids spent indoors on devices made their myopia worse.

But time spent doing near work, in and of itself, did not cause nearsightedness.  So, the belief that too much time spent on the iPad/iphone will cause a child to need glasses is incorrect.  I am asked this leading question at least daily by parents “Using the iPhone or playing video games is bad for the eyes, right?”  .  They look at me hopefully, expecting me to dispense a lecture to the kids of the dangers of said devices.  But, unfortunately, it’s just not true.  Now, what I do tell them, is that first and foremost, too much time spent on these devices is not great for their brain.  A policy statement issued  by the American Academy of Pediatrics warned about the dangers of attention problems, sleep difficulties and obesity from too much time spent on media devices.  However, there have been no conclusive studies which link media devices with eye or vision problems.  BUT, when kids are playing on these devices, it does make it more difficult to get them outdoors, in the protective UV light and that can make them more nearsighted. So, is it the bright light or the UV light that’s protective?  Well, studies in animals seem to indicate that it might just be bright light which is helpful, though it’s still too early to draw conclusions.  However, I still recommend that kids should always wear protective hats, sunglasses and clothing when outdoors, especially here in Hawaii.

Being myopic is not just a pain for children to wear glasses, it can also have serious consequences in terms of the health of a child’s eye.  People who are myopic have longer eyes than individuals who are not.  That predisposes them to having retinal tears and detachments if their prescription is higher than -6.00 D.   It’s basically because the same amount of retina is being stretched more in a myopic eye than in a normal eye.  This can leads to areas of thinning or tears which can cause retinal detachments.

 

2.  Atropine 0.01%

Another important study assessed the effectiveness of a dilute version of a dilating drop – atropine – in delaying the progression of nearsightedness.  Studies have been done with different strengths of this drop in the past, but as you may know from going to the ophthalmologist, even when dilute, dilating drops can cause side effects, like blurry vision and sensitivity to sunlight.  But, this study looked atropine 0.01%, which is 1/100th the strength we use in the clinic.  When administered daily to kids, it slowed their nearsightedness and also decreased the elongation of their eyeball.  Therefore, they were less at risk for those dangerous retinal tears or detachments.  I now offer these drops to a high select group of patients who have nearsightedness which is worsening quickly.

Schools in China are already applying the outdoor time in an effort to decrease their incidence of nearsightedness.  And, for those kids for whom this preventative treatment is not enough, then there is hope with the atropine drop.  As more studies come out, the research will be even better in helping us slow nearsightedness in our kids.