Toric lens fitting + soft aftercare

Regular astigmatism: what is WTR?

• Flatter meridian closer to 180°, steeper closer to 90°

• More common in younger gen

Regular astigmatism: what is ATR?

• Flatter meridian closer to 90°, steeper closer to 180°

• Common in older gen

What is irregular astigmatism?

• Due to corneal irregularity. Meridians are not 90° apart

• Associated with corneal injury, dystrophy’s, warpage etc

What is irregular astigmatism?

• Due to corneal irregularity. Meridians are not 90° apart

• Associated with corneal injury, dystrophy’s, warpage etc

How can we tell where the astigmatism has come from?

Compare prescribed astigmatism to the corneal astigmatism from topography/ keratometry

What is corneal astigmatism?

Spectacle astigmatism matches corneal astigmatism

What is lenticular astigmatism?

Spectacle astigmatism but cornea is spherical

What is mixed astigmatism?

When there is a mismatch between spectacle astigmatism and corneal astigmatism

How do you calculate residual astigmatism?

Ocular astigmatism- corneal astigmatism

When can we leave astigmatism uncorrrcted?

• if a suitable toric lens isn’t available - e.g. oblique axis/ high Rx

• Cost

• Px with 0.25-0.75DC may be happy without correction if not driving at night/ CL is for socialising occasionally, astig in non dominant eye.

When should we consider fitting soft toric lenses?

When uncorrected/ undercorrected astigmatism is clinically significant:

• cyl >/0.75DC

• Spherical CLs give poor/ unstable vision

• Stable axis

• Px wants better clarity

• Regular astigmatism

• Prefers soft over RGPs

What types of lenses are there for astigmatism?

• Soft toric (corneal +/ lenticular)

• RGP

  • spherical (corneal only)

  • Toric back surface (corneal)

  • Toric front surface (some lenticular)

  • Bitoric (corneal/ lenticular)

All must maintain a particular orientation.

When ordering CLs for a Px with high myopia/ hyperopia, what must we adjust?

Use BVD to adjust the prescription.

F2 = F1/ 1- dF1

Use the equation on both sphere and cyl:

E.g. Spec Rx -6.00/-1.75×170:

Use equation to change -6.00, and -7.75

Ocular Rx would therefore be:

-5.50/-1.50×170

In which Px would toric lens not be suitable?

Toric lenses are less likely to be successful in Px with:

• very slanting eyes

• Ususual lid closure

• Incomplete blink

• Lax lids (common with older px)

As toric lens rely on lids interacting in a typical way with the lens. Methods of stabilisation available.

What is the Prism ballast approach?

A method of stabilisation in Px with unsuitable eyes for toric lens.

• 1- 1.5 base down prism put into lens

• can lead to reduced comfort and Dk/t

What is the Peri- ballast approach?

Another approach for stabilising eyes that are unsuitable for toric lenses

• 2 types: traditional/ similar to double ‘slab off’

• Prism free optic zone surrounded by thinned comfort zone/ lenticulation

• Prism reduced significantly but not all lenses are completely prism free for all Rx

Methods of stabilisation for toric lenses in unsuitable eyes: Dual thinned zone

• similar to peri- ballast- thinned too and bottom

• More of a ‘double slab off’

• Termed dynamic stabilisation. Rx independent approach

• Thickest areas at 4 and 8

• Edges thinned- may help with comfort

What is the accelerated stabilisation design?

• 4 zones of thickness consistently correct with blink. Top of lens is thinnest

• Reduces use of gravity and in theory can work without being upright

• Active zones rotate with blink

What are some things to note when fitting a soft toric lenses?

• Discuss vision, cost, pros, cons

• Choose modality/ material

• Calculate BVD effect, then choose prescription

• Select mod BOZR trial lens/ flatter of the two.

• Typically under correct the cyl if you can’t find the exact value

• Look for the toric markers when examining fit. Examine orientation using the rotating slit

• If orientation is poor, consider alternative lens design with diff method of stabilisation

What if the lens orientation isn’t stable and rotates?

Remember the rule: LARS

Left Add, Right Subtract.

E.g. we want 40°. But it keeps rotating 20° anticlockwise. So 40-20=20. Use 20° cyl instead.

Give an example of a soft toric lens

Johnson and Johnson Acuvue oasys for astigmatism

• SiH

• Available in sphere powers of +6.00 to -9.00D

• Cyl powers -0.75, -1.25, -1.75, -2-25 in 10° steps

• 1/52 or 2/52

What are some typical difficulties with soft toric lenses?

• discomfort as thicker lens

• Handling issues (larger TD)

• Hypoxia under thicker lens portion (less of a problem with the stabilisation techniques and available SiH)

When should your first AC appointment be with new Pxs?

Within 1 month (depends on modality)

E.g. monthlies- before end of month. Weeklies- before end of week. Etc.

Second AC: 1-6 months depending on 1st AC outcome

Subsequent; 3-12 months

What’s involved in an AC appointment?

• History and Sxs

• VAs

• Assess lens on eye (condition, fit, pre lens TBUT)

• Lens removal

• Anterior eye assessment (SL, tear tests, keratometry readings)

• Recommendations/ advice

• Issue a specification

General considerations for AC appointments

• Px must attend wearing lenses at least for a few hours (unless sore eyes)

• Case, solution and specs should be brought

What are some general AC outcomes?

• Change lens radii/ diameters

• Change power/ material/ lens type

• Solution change

• Change wearing schedule

• Re instruct hygiene/ handling

• Cease lens wear

• Referrals