2) High power lens

What are the best lens and frame choices for high prescriptions (high plus or high minus)?

Both

• ↓ eye size frame (to cut off excess ET in (-) & overall weight in (+))

• ↓ vertex distance

• frame PD = patient's PD.

• ↑ n (for thinner, lighter lens)

• AR coating to ↓ reflections

.

High (-) lenses

• use hide-a-bevel to ↓ myopic rings

.

High (+) lenses

• aspheric lenses (↓ lens thickness)

How does an aspheric design affect high (+) lenses?

• periphery is flattened → ↑ ET (thickens)

• flatter front surface allows a plano slab to be removed → ↓CT (thinner)

How does an aspheric design affect high (-) lenses?

↓ ET by:

• Steepening the front periphery

• Flattening the back periphery

True or False - Both aspheric and atoric lenses can be single vision, multifocal, or progressive.

True

What are Lenticular Lenses?

→ central area with the proper rx (aperture) + outer skirt is plano/near plano (carrier)

• useful for high powered (+) or (-) lenses

• carrier size is adjusted to fit the frame

What is the Welsh 4-Drop?

→ 24 mm central area surrounded by 4 concentric rings where each drops by 1.00 D in power

• type of lenticular lenses

How does shape mag and power mag change for (+) lens?

↑ shape mag

↑ power mag

How can (-) lenticulars be made?

• very flat BC

• (-) BC → minus "bowl" in the lens center

What is myodisc?

→ trade name for high (-) power lens, where only in the center (the bowl), and the rest of the lens is thin and plano(the carrier)

• BC = flat

True or False - Bowl sizes and power are dependent on each other.

No

For what lens powers does vertex distance and it’s role on F_effective come into play?

greater than +/-4.00

How does changing vertex distance affect the effective power of a lens and the prescription?

Move lens farther from the eye → lens become effectively more (+)

• prescribe more (-)

Move lens closer to the eye → lens becomes effectively more (-)

• prescribe more (+)

• this is why CL Rx is more plus than glasses

What prismatic effects are induced in a high (-) vs high (+) lens?

High (-) = diplopia

High (+) = ring scotoma — "Jack in the box" phenomenon

What is Aphakia? What refractive error does it create?

→ crystalline lens is absent from the eye

• large amount of uncorrected hyperopia (b/c eye becomes more minus → hyperopia)

• if aphakic in 1 eye, the anisometropia created with the aphakia → aniseikonia

What is Pseudophakia? How can the patient can aniseikonia?

→ crystalline lens has been replaced by an artificial lens

• if pt has substantial Rx before cataract surgery and pseudophakia brought them to plano in one eye, the anisometropia → aniseikonia

What is the best way to correct for Aphakia?

→ via CL

• CL is worn close to the entrance pupil → dramatically ↓ mag

• since CL moves with eye, it ↓ aberrations

What is an IOL?

→ artificial lens implanted inside the eye at or near the location of the natural lens

• gives plano rx (but residual astigmatism or ametropia, it can be fixed with "normal" glasses)

• 1 piece or 3 piece

• haptic holds the lens in place

• aim for distance, near, or monovision

What are the different locations/types of intraocular lenses (IOLs) and why did placement change over time?

Early IOLs: Placed in the anterior chamber with haptics resting in the angle → high risk of GLC due to damage/interference with aq drainage, so iridectomy was commonly performed to prevent pupillary block

Iris clip IOL: Attached directly to the iris for support

Sutured AC IOL: Anterior chamber IOL secured sutured to the iris

Modern IOLs: Usually placed in the posterior chamber within the capsular bag

List the 3 potential problems you can run into with IOLs. Name the respective visual problem associated with it.

1. Tilted → astigmatism

2. Mis-placed → prismatic effect

3. Displaced/dislocated → diplopia

   • caused by trauma or weak zonules

How can multifocal IOL account for distance and near vision?

via concentric zones

How are accommodative IOLs placed?

→ placed in the capsule

• have hinges that bend when the ciliary muscle moves (to allow for accommodation)

Why are UV-blocking IOLs important after cataract surgery?

→ natural lens normally absorbs UV light, protecting the retina

• retina can be exposed to harmful wavelengths after lens removal surgery

• Modern IOLs block UV light and ↓ short-wavelength transmission to mimic the protective function of the natural lens

How does age affect blue light transmissions?

↑ Age = ↓ blue light transmitted (↑ absorbed)