A manual Keratometer is used to measure corneal curvature in the eye. It is also known as an Ophthalmometer. These both do the same job by manually measuring the size of an image that is reflected against the cornea, you then measure the distance between two points and how far they are apart. This method is then calculated and measures the curvature of the cornea.
The reason for wanting to measure the curvature of a cornea is usually to fit contact lenses that are the perfect fit or in pre operation tests for cataract surgery.
The manual Keratometer has doubling prisms inside it that make the image clearer and help to give a more accurate measurement.
This reading will be the dipodic formula of the cornea. To find the curvature, you must use the calculation that is in Snells law of refraction with simplified optics.
This formula is calculated as D=N-1/R.
D = the dipodic formula of the cornea.
N = the refractive index of Keratometer used (this is usually 1.3375) you will minus 1 from this to take into account the fact that there is a layer over the cornea that makes it a slight thicker.
R = Radius curvature of the cornea.
As you will usually have the figure for D from your Keratometer, you will have to switch your calculation around so that it reads R=N-1/D. You will be able to work out now what R is and find out the radius of the cornea.
The manual Keratometer is said to be just as accurate as an electronic one if you make sure that it's used correctly to get the reading and if the formula is implemented properly when dong the math with your reading.
The reason for wanting to measure the curvature of a cornea is usually to fit contact lenses that are the perfect fit or in pre operation tests for cataract surgery.
The manual Keratometer has doubling prisms inside it that make the image clearer and help to give a more accurate measurement.
This reading will be the dipodic formula of the cornea. To find the curvature, you must use the calculation that is in Snells law of refraction with simplified optics.
This formula is calculated as D=N-1/R.
D = the dipodic formula of the cornea.
N = the refractive index of Keratometer used (this is usually 1.3375) you will minus 1 from this to take into account the fact that there is a layer over the cornea that makes it a slight thicker.
R = Radius curvature of the cornea.
As you will usually have the figure for D from your Keratometer, you will have to switch your calculation around so that it reads R=N-1/D. You will be able to work out now what R is and find out the radius of the cornea.
The manual Keratometer is said to be just as accurate as an electronic one if you make sure that it's used correctly to get the reading and if the formula is implemented properly when dong the math with your reading.
