GPCLs for Astigmatism and Presbyopia

2

If the patient has corneal cylinder that is less than ___ D and it matches the refractive cylinder, the patient can be fit to a spherical GPCL as the tear lens will neutralize the astigmatism

vertical, horizontal

If a patient needing a toric GPCL is fit to a spherical lens, a patient having WTR cornea will display ____ lens decentration and a patient having ATR cornea will display ____ lens decentration. This may provide adequate vision, but it will be fluctuating and uncomfortable

Residual astigmatism

the cylindrical refractive astigmatism remaining after neutralization of the corneal cylinder by the tear lens

Front toric (F1 toric)

toric GPCL lens design that is analogous to a toric soft lens where there is a need for some form of lens stabilization in order to keep the refractive power aligned due to insufficient corneal toricity to stabilize the lens during blinking. Is indicated for corneal cylinder <1.50 with >1.50 refractive cylinder. Low corneal cylinder with >0.75 D of residual astigmatism with a spherical GPCL.

1.5, BD, inferiorly, diameter, optic zone

Stabilization of a front toric GPCL involves ____ prism diopters of ___ prism that will result in decentration of the lens slightly ____ and therefore requires a slightly larger ____ and ____

Back surface toric/spherical front

toric GPCL lens design that induces residual astigmatism that is equal to and opposite of the refractive astigmatism via difference in refractive indices between the CL material and tear film. Induced cylinder will be minus with the axis the same as the flat meridian of the cornea. Cost is slightly less than a bitoric lens.

half

The cylinder induced by a back surface toric spherical front lens will be equal to ____ the amount of toricity of the contact lens base curves

1.5

The ideal patient for a back surface toric spherical front lens is a patient whose refractive astigmatism is ___x their corneal cylinder both being at the same axis

Back surface/bitoric (F2 toric)

toric lens design where the back surface base curves approximate the corneal curvature in the principal meridians creating a near plano tear lens and refractive power ground on the front surface. Is indicated for corneal cylinder >2 D regardless of refractive cylinder.

Full alignment

bitoric lens design where the back surface base curves exactly align with the curvature of the cornea to create a plano tear lens. Lens does not have much movement, so these lenses are ideal visually but not physiologically especially as toric lenses are generally thicker as well. Ultimately, poor tear exchange!!

Low toric simulation

bitoric lens design where back surface base curve is slightly altered to allow for better lens movement when compared to full alignment. It is usually fit 0.25 D flatter than the flat K, 0.50-1.25 D flatter than the steep K. Lens is made slightly larger in diameter to compensate for increased lens movement.

Spherical power effect

bitoric lens design where the difference in base curves of the lens is equal to the difference in lens power. Occurs because refractive astigmatism is nearly all corneal. Optically performs like a spherical lens whose power is not impacted by lens rotation

Cylindrical power effect

bitoric lens design where the over-refraction using an SPE design reveals >0.75 D residual astigmatism. Occurs because refractive astigmatism is not entirely corneal. Power is impacted by lens rotation.

HVID, lid position, and mesopic pupil diameter

The lens diameter and optic zone diameter of a GPCL will depend on these three factors

spherical

If toricity of the cornea is primarily central, use ____ peripheral curves

toric

If toricity of the cornea is limbus to limbus, use ____ peripheral curves to increase lens stability with blink

better

Multifocal GPCLs provide ____ vision than soft contact lenses due to the high optical quality of the lens material

Rotational

multifocal RGP design that keeps distance and near segments visually accessible even when the lens rotates under the influence of a blink. Is a distance vision center with a surrounding near vision segment.

Non-rotational

multifocal RGP design that resembles a bifocal spectacle lens with the distance vision segment on the top and the near vision segment on the bottom. The lens cannot rotate, but moves vertically to maintain vision at distance and near.

Aspheric

multifocal RGP design where the center of the lens is distance power. Lens power gradually increases in plus power from the center so that when the gaze shifts downward the patient is looking through a near add. This is achieved by a gradual change in curvature of the lens. Mimics a PAL.

simultaneous

Aspheric multifocal RGPs function optically via ____ image

early to moderate

Aspheric multifocal RGPs work best for ____ presbyopes

higher effective add power

New multifocal RGP aspheric lenses incorporate front and back curvature to allow for _____

decreases

In aspheric multifocal RGPs, as effective near power increase, the distance power zone diameter (increases or decreases)

small to medium

Aspheric multifocal RGPs require a ____ pupil size under average room illumination to minimize glare and ghosting at night induced by paracentral and midperipheral plus power

1, 3

Aspheric multifocal RGPs should have limited movement of about ____ mm. Early designs were fit as much as ___ D steep to minimize lens movement

corneal topographic changes, effective add power

A back surface designed aspheric RGP multifocal which is decentered may induce ____. Front surface designs can be used to avoid this and can also have a greater ____

Translating

multifocal RGP design which has a distance vision segment that is aligned with the visual axis in primary gaze, and a near vision segment that is aligned with the visual axis in downgaze. Requires a stabilization system to keep the lens in the optimal position (prism ballast or truncated). Mimics a bifocal or trifocal.

alternating

Translating multifocal RGPs function optically via ____ image

1.5

A translating bifocal RGP fit may be difficult if the lower lid margin is >___ mm above the lower limbus

lower pupil margin

The seg height of a translating bifocal RGP should be at the ____ in primary gaze under average room illumination

1-3 BD

____ prism is incorporated into translating bifocal RGP lenses to maintain lens orientation

50

The near segment of a translating bifocal RGP should cover at least ___% of the pupil in downgaze

0.4

A truncated translating bifocal RGP lens is ____ mm smaller vertically than it is horizontally

prism

If a translating bifocal RGP is lifting off of the eye too much with blink, increase ____ to increase the mass of the lens

edge lift, flatten

If a translating bifocal RGP is not translating adequately with downgaze, increase ____ or ____ the fit to promote more movement