Astigmatism

Describe the demographics of astigmatism

Little change in astigmatism from ages 6-16

Increase in ATR astigmatism beyond age 35 (0.20D per 10 yrs)

High astigmatism (WTR) = common in central american native populations (can range 5D and beyond)

WTR astigmatism common in Asians

What are the symptoms of astigmatism

Distance blur (miss 1-2 letters on several lines of the chart that are often similar in shape)

Eye strain with WTR (squinting)

Sometimes near blur, pt can compensate by moving closer

Double vision, shadows, ghosting

What are the signs of astigmatism

Corneal toricity

Cataracts

Trauma

Pterygium

Ptosis or proptosis

Keratoconus (and other corneal diseases/degenerations)

Amount of astigmatism can change significantly in

Young children

When is the near adult level of astigmatism develop

Around 6 yo

What should be prescribed at a young age with astigmatism Rx

High amts of astigmatism correction to prevent meridional amblyopia (as little as 1.50 DC can be amblyogenic)

Patients 2-6 yo should be presecribed

Full amount of astigmatism for full time wear if astigmatism is stable and recheck pt in 3 months

Patients with astigmatism from 6 to teens should be prescribed

Prescribe full amt for young pts but know adaptation problems can be an issue (recommend full time wear)

Older part of this age range might need trial framing

Adult patients with astigmatism should be prescribed:

For pts that are more adaptable, give full Rx at the beginning

BE WARY OF CHANGE MORE THAN 0.75 DC

Can compromise Rx for highly sensitive patients (give spherical equivalents)

What is high astigmatism associated with

High hyperopia and myopia

Higher astigmatism and oblique axes are

Harder to adapt to

What is the treatment for irregular astigmatism

Spectacle Rx is a compromise

Better results with CL or refractive surgery (intacs in US; corneal collagen cross linking in Europe)

What does a rotation of 10 degrees for astigmatism axis result in

Uncorrected error 1/3 of power of the lens

Rule of 30 holds true up to

40 degrees away

If the patient has -1.50 x 090 cylinder which you correct with -1.50 x 100, what is the residual cyl

-0.50 D

If the patient has -3.00 x 025 cyl which you correct with -3.00 x 045 this will result in residual cyl of

-2.00D

What should you beware of when refracting a patient with astigmatism

Axes that are not mirror image symmetrical around major axes

Axes changes in the same direction

Significant changes from previous axis, esp with no change in VA

What should the demo be?

Old Rx -2.00-1.50 x 180
New Rx -2.00-2.25 x 180

Trial Rx over current Rx is -0.75 x 180

What should the demo be if:
Old Rx: -2.00-2.25 x 180
New Rx: -2.00 -1.50 x 180

Put +0.75 x 180 in front of old Rx

You can often cut Rx by how much cyl without causing degradation of acuity?

0.50 cyl

When should you warn patient about adaptation

First time wearers

If there is a significant carnage in cyl power or axis

Different type of frame

When should you warn your patient about uneven size effects

Uneven size effects

When magnification/minification is different in each meridian

Aniseikonia can result in spatial distortions

If high cyl, what frames are best

Small frames bc less peripheral distortion

Choose frame so pupil is close to geometric center of the lens

What are the advantages of centering eyes in frame

Less peripheral distortion

More uniform vertex distance minimizes magnification differences (contacts work better for high astigmats)

Less decentration = smaller lens

When giving a patient the Rx with astigmatism, what should you recommend?

Digital lenses need to have POW measurements: vertex, wrap, and panto as well as OC

Discourage online purchases/other poor quality options

Why should you avoid perfectly round frames for your astigmats

If lens rotates in frame, the Rx will become inaccurate

Optician will no necessarily know proper orientation

Why not rectangular frames for astigmats?

Poor cosmesis for high oblique or ATR Rx