Term
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Definition
Power of the cornea and lens is not strong enough.
posterior surface of the lens does not converge the light enough for a sharp image to be formed on the retina.
the light rays come to a focus behind the retina but the retina blocks this so a blurred image is formed on the retina |
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Definition
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Term
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Definition
Most common
the eyeball is too short
more powerful lense needed to converge the light to a focus on the retina because the retina is closer to the lens of the eye than in an emetropic eye
common in young children - still growing so shorter eye balls |
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Term
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Definition
| Power of the optics of the eye are not powerful enough... the cornea is flatter than that of an emetropic eye therefore less powerful so less convergence takes place, therefore the focus of the light rays would be behind the retina |
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Definition
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Term
| HOW DOES A HYPEROPE SEE CLEARLY? |
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Definition
Convergent light needs to enter the eye
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Term
| OCULAR REFRACTION (IN HYPEROPES) |
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Definition
The convergenc eof light hitting the cornea in order for a clear image to be formed on the retina
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Definition
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| Point where light that hits cornea would converge to if the eye were not there |
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Definition
| Use positive lenses to change the vergence of the incoming light from a dsitant object (zero) to converging light |
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Term
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Definition
| Image focal point of lens must be the same as farpoint if hyperopic eye in order to give the right amount of convergence to give a clear image on the retina |
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Term
| FOCAL LENGHT, SPEC DISTANCE AND FAR POINT |
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Definition
| Spec focal length = spec distance + distance to far point |
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Definition
| ALWAYS USE SIGN CONVENTION |
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Term
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Definition
| The prescription for contacts for hyperopes is always stronger than specs because it's closer to the eye. this is the opposite to myopes |
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Term
| DIFFERENCES BETWEEN SPEC AND CONTACT PRESCRIPTION |
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Definition
| The greater the amount of correction needed, the bigger the difference between contact pres. and spec pres |
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Term
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Definition
Accommodation increases the power of the lens.
hyperopes may be able to see distant object by accommodating
if sufficient accommodation, they can see clearly in the distance but myopes never can |
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Term
| WHY CAN'T HYPEROPES SEE UP CLOSE? |
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Definition
They use the accommodation which they have to focus on distant objects.
No accommodation left to focus on things close up therefore thier near point becomes more further away than usual |
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Term
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Definition
| amount of hyperopia which can be compensated for by accommodation |
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Term
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Definition
| The amount of hyperopia left over when all accommodation has corrected some |
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Term
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Definition
| Absoloute + facultative the total hyperopia is another term for the ocular refraction |
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Term
| WHAT IF ALL THE ACCOMMODATION IS USED UP TO SEE DISTANT OBJECTS CLEARLY? |
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Definition
The near point does not exist so they cannot see anything clearly.
this can happen if they patient has little accommodation left probably due to age and the amount of hyperopia they have exceeds the amount of accommodation availiable. |
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| HOW TO DETERMINE THE FACULTATIVE HYPEROPIA |
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Definition
| Subjective refeaction - the smallest positive lense added which allows the patient to read the 6/6 line gives the absoloute hyperopia whereas the highest plus power lens which allows the patient to see the letter chart clearly gives the total hyperopia. the facultative can be calculated from this |
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Term
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Definition
Seems to be more hyperopic using ret than subjective tests. accommodation is more releaxed during ret than by subjective tests but unknown as to why.
in ret the accommodation is still not completely relaxed however |
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Term
| HOW TO GET TOTAL HYPEROPIA |
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Definition
| Accommodation is not totally relaxed during ret therefore a cycloplegic drug is used to paralyze the ciliary muscles to completely relax the accommodation while doing ret |
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Definition
| Hyperopia measured by subjective methods |
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Definition
| The difference between subjective (mentioned before) and objective (ret using cycloplegic drug) |
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Definition
Like facultative hyperopia, however it does not disappear by increasing the power of lenses
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Term
| PROBLEMS OF LATENT HYPEROPIA |
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Definition
People can't immediatly see clearly in the distance when specs are prescribed to them
if only manifest hyperopia is corrected, the patient can see clearly in the distance, however some accommodation is still used to correct the latent hyperopia so the near point is still further away than usual |
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