Hello there and welcome to the clinic so today we're going to be looking at
your ocular prescription so you can get a better understanding of what all those numbers mean on
that little slip of paper you're given at the end of your eye examination. So just looking at some
of the columns you'll see on your prescription you have your spherical lens prescription here, your
cylindrical reading, the axis that the cylinder sits at, if any prism has been prescribed
to help your two eyes work better together, that will be included here. If you are presbyopic, if
you are of a certain age and you are struggling to read you may have been prescribed a reading add.
You may even be prescribed an intermediate add for your arm's length work such as working on
the computer and this is where, if required, the prism of your near comes into play. Again if you
have any problems with the two eyes working together at near you may require some prism.
Okay so you have your right eye readings this row here and your left eye now on some
prescriptions you may see the right eye written as od, left eye written as os these are just
Latin abbreviations for right and left, sphere units
dioptre sphere, cylinder for your astigmatism if there's any present dioptre cylinder, axis
in degrees, prism, add diopter sphere and so on, so let's take an imaginary prescription
and have a little look at things. Let's say in the right you are a plus two sphere
minus one cylinder atan axis of one hundred degrees. I'll just ignore
this part for now and in the left eye let's change it up you are a minus one
sphere and you have a cylinder
minus 0.50 that sits at an axis of 80 degrees there so that is your prescription,
so we're going to take the right eye first now just focusing on the spherical column here
if you see a plus symbol before the number here that means you are
long-sighted or
hyperopic
conversely if you see a minus a symbol before your sphere opposite you are short sighted, you are
myopic. And if there are any numbers present in the cylindrical column there that means you have
some, as well as long or short-sighted if there's numerical values values there, you are or you have
you have astigmatism you have rugby ball
shaped eyes which is a term commonly used by optometric professionals to just describe
astigmatism. This is rugby ball-shaped eyes. The astigmatism could be coming from the
cornea of the eye or it could be from the crystalline lens there
lens cornea or it could be a combination of the two combined there generating the astigmatism.
Because one meridian is steeper than the other we have to note the axis that the cylinder sits at
so that is your prescription. Those are the lenses that should give you best vision for your everyday
needs. So when we're thinking about long-sighted hyperopic, if I can just try and draw an eye here
cross-sectional view there the light coming in, when you are hyperopic the light is
focusing behind the retina at an imaginary point there so we will place a positive lens in front
a convex lens and the light then hopefully, if this lens is correct, should focus
on the retina and again the opposite here there is your eye if you are short-sighted
the light is focusing somewhere in front of the retina there.
That is your light source coming in, light is focusing here you shall require a concave lens
to cause the light to diverge and focus on the retina, thus giving you the best vision
possible. if you are presbyopic so you're wearing your general prescription but you
are also having problems focusing on your reading vision, you might be prescribed a reading add.
the add required usually gradually increases with age
so that should focus your new vision and you may have been prescribed an
intermediate add for those tasks you perform at an intermediate distance to just the VDU
So the optometrist should measure your working distance and calculate
and demonstrate what lenses are going to best focus your intermediate there. The
symbol is always plus with your add and intermediate adds there, now if you wanted to
work out your reading prescription, just your reading prescription, take the plus one add
add it to the two, so reading in this case,
near, talking about your reading not intermediate one two would be plus three,
keep the cylinder there, axis remains the same, so that is how you calculate your near
For the left eye near vision prescription,
plus one, add it to the minus one spherical element that becomes plano/zero
cylinder remains the same
and that is your near near vision prescription based on these values here, lovely
so that in a nutshell is your prescription and now something else you may see
on your prescription abbreviated to BVD this is your back
vertex
distance. It could be somewhere um in the range of size 6 millimeters to 15, for example,
always in millimeters. This reading is basically the distance that the lens in the trial frame sits
from your eye there,
so you should be able to measure that distance, that is your back vertex distance, the distance
between the front of the cornea here and the back of the lens in the trial frame that you are using
and back vertex distance is important to note in your higher prescriptions anything beyond
four to five and that's also useful if we're looking to fit the patient with contact lenses
because the contact lens sits on the surface
of the cornea there literally makes contact so the prescription required for your contact lenses
may be different depending on the strength to your general glasses prescription.
So I hope that has helped to demystify a few things about the prescription that you are given
after your eye examination. Obviously prescriptions can change over time
depending on the age and some of the work you do. Reading additions tend to come up with age
so that's why it's important to follow your optometrist's recommendations
regarding when your next eye examination is due. And I'm just going back to the prism element and
the prism is basically something that bends the light which may be incorporated if you are showing
that your two eyes are not working well together as a team the prism may help relieve your
diplopia for example or double vision or if you have a phoria
that's causing you some problems, whether that's distance or near the prism can help to relax
the eyes keep everything binocular single and comfortable and when we record prism we should
measure it in the vertical and horizontal meridians and we will put say the value of
the prism prism measured one and it's important to say whether the prism is base out, base in,
up or down depending on the readings taken and the tests before. Let's just say this is base out
and base out so overall combined you would have two dioptres out combined for your glasses
prescription there. Okay so that is everything today. If you have any further questions about
your eye prescription or there's something I didn't cover, just let me know in the description
and I will try my best to answer your questions so see you next time in the clinic, bye for now.