Refractive Error & Far Points

emmetropia

no refractive error

ammetropia

has a refractive error

myopia

light focuses in front of the retina (corrected w/ a minus lens)

where is the far point for a myope?

in front of the eye

low myopia range

>-3.00

medium myopia range

-3.00 to -6.00

high myopia range

< -6.00

what is another term for far point?

Punctum remotum (PR)

refractive myopia

refractive elements of the eye are too powerful

axial myopia

eye is too long

night myopia

increase in myopia in low light

purkinje shift

eye shifts sensitivity to wavelengths that are more refracted from dark(scoptopic) to light (photopic)

pseudomyopia

• spasm of ciliary body accommodative response

• can be reversible

• not a true refractive error

hyperopia

light focuses in back of the retina (correct w/ plus lens)

where is the far point for a hyperope?

behind the eye

low hyperopia range

<+2.00

medium hyperopia range

+2.25 to +5.00

high hyperopia range

> +5.00

refractive hyperopia

refractive elements not powerful enough

axial hyperopia

eye is too short

manifest hyperopia

maximum plus correction that patient will wear, not always all of the total hyperopia

latent hyperopia

amount of hyperopia revealed only w/ cycloplegic agent

facultative hyperopia

can be overcome by accommodation

absolute hyperopia

can NOT be compensated by accommodation

anisometropia

more than 1D difference in power between the eyes

isoanisometropia

more than 1D difference but both eyes either myopic or hyperopic

antimetropia

one eye hyperopic, one eye myopic

accommodative amplitude

total amount of accommodation you have……………

simple myopic astigmatism

• one emmetropic meridian (Far point at infinity/on retina)

• one myopic meridian (Far point in front of eye)

simple hyperopic astigmatism

• one emmetropic meridian (far point at infinity/on retina)

• one hyperopic meridian (far point behind the eye)

compound myopic astigmatism

both meridians myopic (far points in front of eye)

compound hyperopic astigmatism

both meridians hyperopic (far points behind the eye)

mixed astigmatism

• one meridian myopic (far point in front of eye)

• one meridian hyperopic (far point behind the eye)

the amount of accommodation for an emmetrope

inverse the target distance (1/distance)

the amount of accommodation for a hyperope

sum of refractive error plus inverse of the target distance (1/distance + RX)

the amount of accommodation for a myope

difference of the refractive error and the inverse of the target distance (1/distance - RX)

a 0.37 mm change in axial length is equal to…

1.00 D change in refractive power of the eye

how do you know patient is not really myopic?

• variable VAs

• dilation (paralyzes accommodative system > decrease the amount of myopia)

• evaluated accommodative process

the closer the far point is to the eye…

the higher the refractive error gets