Chapter 10: Intraocular Lenses

What are the limitations of anterior chamber phakic IOLs (tucked in between cornea & iris)

-can't be used for shallower AC depths (<3.2 mm) = excludes a lot of hyperopes -Complications (endothelial cell loss, glare)

Expectations for Standard IOLs

-cheaper -will correct for distance or for near but not both (will need to wear readers) -if they have corneal astigmatism they will still need distance gls to correct it.

What are the posterior chamber IOL implantation sites?

-ciliary sulcus (stitched in place = complications) -capsular bag

SRK I formula and its limitations

-early formula that only took into account axial length and mean corneal power P = A -2.5L - 0.9K P = IOL power for emmetropia A = constant based on IOL type L = axial length of the eye K = average total corneal power based on keratometry ** this did not take into effect axial length extremes

Why do hyperopes have less success with corneal refractive surgery

-easier to flatten a cornea to correct for myopia but it is hard to create appropriate curvature for hyperopia

Expectations for Multifocal IOLs

-expensive -equivalent of a multifocal CL -glare & halos -short adaptation time -will likely not need glasses

What was the main complaint regarding accommodating IOLs?

-glare -the haptics in the IOLs must be larger to allow the lens to shift forward -sometimes at night, the pupil is larger than the small optic zone of the IOL -will see glare due to the edges

What are the limitations of Posterior chamber phakic IOLs/collamers -between the iris and the lens

-good for hyperopes but can cause: -Contact with anterior lens causes anterior subcapsular cataract -Iris problems also occur, pigment rubbing off -PC location means higher lens power required than "equivalent corneal power" change with LASIK

Accommodating IOLs -mechanism & structure

-haptics prevent rotation but are flexible w/ hinges to allow forward and backward motion -have to be placed in the capsular bag -when ciliary body moves forward there is vitreous pressure on the posterior capsule that moves it forward. -need accommodative therapy since accommodative muscles haven't been used.

What are "refractive" Multifocal Lenses

-optical zones of varying diameter -almost like there are buffers between each zone to prevent halos -distance in the center -gives better intermediate vision

In the past, cataract surgeries were intracapsular. What does this mean?

-removal of the entire crystalline lens -needed large incision, AC placement, and rigid IOL -post-surgical astigmatism & long healing times

Three-Variable Formulae (SRK-T)

-takes into account iris location (aka AC depth)

Now, modern cataract surgeries are extracapsular. What does this mean?

-the capsule remains intact -smaller incision w/ flexible IOLs designed to sit in the capsule

When is ciliary sulcus IOL placement used?

-used mainly for piggy-back IOLs (e.g. after refractive "surprise"), or for phakic implants

• Patient 1 AC depth = 2.8 mm • Patient 2 AC depth = 3.6 mm (= standard emmetropic eye AC depth) • Patient 3 AC depth = 4.4 mm Using the SRK I formula to calculate IOL would result in what type of ametropia for each patient?

Patient 1 AC depth = 2.8 mm -patient's IOL will be placed too far forward and will cause patient to become myopic (can see fine to read but distance is blurry) Patient 2 AC depth = 3.6 mm -Patient will be emmetropic since this is what the SRK I formula was based on Patient 3 AC depth = 4.4 mm -patient's IOL will be placed too far back and will cause patient to become hyperopic (cannot see to read (no accomm.) or distance)

The more anterior an IOL is placed, the lower/higher the actual power should be to focus a distant object on the rertina

The lower -as an IOL is moved forward, the more positive it becomes, to counteract this change, the IOL power must be made lower.

IOL power must be the lowest when placed in the... a) ciliary sulcus b) anterior chamber c) capsular bag

b) anterior chamber

IOL power must be the highest when placed in the... a) ciliary sulcus b) anterior chamber c) capsular bag

c) capsular bag

The best multifocal IOLs to date are refractive/diffractive lenses. In terms of patient satisfactions, these IOLs are: a) better tolerated than monofocal single vision IOLs b) tolerated about the same as monofocal single vision IOLs c) not as well tolerated as monofocal single vision IOLs

c) not as well tolerated as monofocal single vision IOLs

As AC depth increases, required IOL power increases or decreases?

increases -IOL will sit farther back, weakening it

disadvantages of Intraoperative Wavefront Aberrometry (ORA)

-Adds a few extra minutes to surgery time -Most patients do not require the use of Ora for a desirable outcome -Has a learning curve for the surgeon -Average cost to the patient is an additional $337 per eye -Additional cost to the surgeon

What are "Adjustable" Power Aphakic IOLs (non-accommodating)

-Allows real-time, operative modifications for IOL power -Gives surgeon the ability to correct any error in IOL power calculations

What are Array Multifocal IOLs

-Alternating distance and intermediate/near zones -better than 2-Zone -complaints: lower contrast sensitivity & increased perception of halos

Advantages of Intraoperative Wavefront Aberrometry (ORA)

-Confirms surgeons calculations for better quality outcomes -Can customize cataract surgery and reduce the need to wear prescription glasses afterwards -Specifically helpful for the more advanced surgical cases including those with: ○ LASIK ○ PRK ○ RK ○ High amounts of astigmatism

What are Combined Refractive / Diffractive Multifocal IOLs

-Diffractive lenses "focus" longer wavelengths more strongly -Refractive lenses focus shorter wavelengths more strongly. -What happens if you use a combined refractive/diffractive? You can reduce longitudinal chromatic aberration (LCA) -works well for small & large pupils but patients will still complain about halos

What are Phakic IOLs

-IOLs placed into the eye with the lens still remaining -much lower power since eye still has ~+20 D from lens -just in front or behind the iris PROs -alternative to corneal refractive surgery -Reversible (not like LASIK or PRK) -for those who have thin corneas or endothelial corneal disease -new technology allows for good corneal measurements with these implanted, not like with LASIK or PRK.

Structure of 2-Zone Multifocal IOLs

-The peripheral zone is focused for distance vision -central zone for near vision • Both zones contribute reasonable acuity for intermediate vision **having the central zone could be a problem if they are trying to read in the bright sun

What is Intraoperative Wavefront Aberrometry (ORA)

-a scanning instrument that uses wavefront aberrometry to measure the refractive power of the eye after the lens is extracted for optimal results. -Measurements are used to determine what kind of IOL to use or if corneal relaxation incisions are needed in conjunction with an IOL for higher astigmats.

Describe what a staar lens is

-a single silicone piece that can be folded and placed into a capsular bag -standard capsular bag IOL

SRK II formula pros and limitations

-allows for errors at the extremes of axial length with SRK I -Makes adjustments to IOL "type" constant, A based on axial length. *Dr. O says she will provide this chart for questions limitations: does not take into account anterior chamber depth

PROs of an aspheric Refractive IOL

-allows manipulation of negative IOL spherical aberration to balance positive corneal Spherical Aberration -flattening at the periphery

Why are older patients (70-80) not the best candidates for accommodating IOLs?

-atrophy of ciliary muscles -liquefication of the vitreous causes less pressure = unable to effectively move IOL forward

Toric IOLs -function & structure

-can correct up to 2-3.50 D of astigmatism -anterior surface is spheric -toric posterior "optic" zone -have haptics (arms) to minimize rotation -only corrects corneal cyl because the physiologic cyl from lens is gone

According to IOL manufacturers, errors in ocular biometry (axial length measurement) account for around half of all postoperative surprises after cataract surgery. What method of measurement is most prone to error?

Applanation ultrasound A-scan axial length measurement is the procedure most prone to operator error -unfortunately needed if cataracts are very dense

PanOptix Trifocal IOL -structure -pros -con

structure: -focal points at optical infinity, 60 cm, and 40 cm -toric option -anterior surface is aspheric, posterior is spheric Pros: -vision less dependent on pupil size or lighting conditions -contrast sensitivity is okay Cons: -halos -glare

After cataract surgery does the emmetropic eye become hyperopic or myopic?

the emmetropic eye becomes about 12 D hyperopic