3 SCL Exam and Fitting

Exam schedule for a neophyte

Baseline exam → 1-2 wks dispense and I&R → 1-2 wks F/U → yearly exam

New extended/Continuous wear F/U

Baseline exam + dispense → if needed, 1-2 wks dispense OR 1 day F/U after first overnight wear (evaluate vision, comfort, corneal edema) → 1-2 wk F/U → 6 mo. long term F/U to assess hypoxic changes → yearly exam

Veteran Daily wear F/U

Yearly exams. If need re-order or re-fit, 1-2 wk dispense → 1-2 wk F/U → rare 1-3, or 6 mo F/U → yearly exam

Components of prefitting/comp exams

• CL History

• Measure corneal shape (Ks/curvature, asphericity, HVID, sag depth)

• ManRx, vertex is needed

• Slit lamp (eyelid eversion, tear film eval)

• BV eval

CL Fitting: Lens selection occurs at three types of exams

1. Stand alone visit

2. Comprehensive exam

3. Dispensing visit

Specific lens is chosen for patient based on these factors:

• Modality (DW, EW, CW)

• Disposal schedule (daily, weekly, two-weeks)

• Brand/BCR based on sag depth

Parts of a CL fitting

• Settling time

• Fitting relationship assessment (centration, coverage, movement, pushup test)

• VAs

• Over-refraction

• Surface evaluation at Comprehensive and Progress Checks

Dispensing Exam procedures

• Entrance VA in habitual correction

• Brief history (any changes)

• Assess fit

• If good fit and minimal over-refraction, educate pt and send home OR re-fit/reorder and repeat dispensing exam

Progress Check procedure

Same as dispensing visit

• Entrance VAs with dispensed lenses

• Brief history (any changes?)

• Assess fit

• Educate pt (I&R) and send home until comprehensive exam, OR reorder and repeat dispensing exam

Questions in CL History

• What lenses worn? How many years?

• Wear schedule? Disposal schedule? (Make them open ended!)

• “How often do you sleep in your contact lenses?”

• Which solutions?

• Ask about hand washing

• “Tell me what you do with the case after you put your lenses in”

Ways to measure central corneal curvature

• Keratometry (Auto Ks)

• Corneal topography (Ks and Asphericity

Ways to measure HVID or WTW

Horizontal Visible Iris Diameter or White-to-white

• PD ruler

• Topography

Mean corneal power/curvature

43.50 ± 1.7

Mean corneal astigmatism

0.9 ± 1.1D

Average HVID

11.5mm

An unusually spherical (not aspheric) cornea results in a [shallower or deeper] sag than aspheric?

Deeper

Axial vs Tangential maps for corneal topography

• Axial maps represent best optical characteristics of the cornea

• Tangential maps represent true curvature data, and give better peripheral shape information

Which corneal topography maps are preferred in refractive surgery, axial or tangential?

Axial, represent best optical characteristics of the cornea

Which corneal topography maps are preferred in CL practice, axial or tangential?

Tangential, represent true curvature data, and give better peripheral shape information

Mean corneal sagittal depth

2.74

T or F, corneal curvature is sufficient to explain how deep or shallow the contact lens needs to be for good fit

F, sagittal depth is needed to explain the fit of a CL

What factors determine sagittal depth?

• Corneal curvature (radius of curvature in equation)

• HVID (chord diameter in equation)

• Asphericity

What factor best predicts the adverse effects, dropout, and discomfort of a CL?

Sagittal depth

Are CLs thin or thick lenses?

Thick lenses

How do we change sagittal depth of a soft CL?

Choose a different brand (soft lens manufacturers usually offer only one fit)

How do we measure corneal sagittal depth?

Take measurements parallel to the scanning beam on AS-OCT (anterior segment), and divide by refractive index of material

People with adverse effects related to CL wear had corneal sag depth [shallower or deeper] than the population mean

Shallower, the CL was too tight like a suction cup

CL wearers that dropped out/discontinued had corneal sag depth [shallower or deeper] than the population mean

Both shallower and deeper than the population mean

What symptom was more likely to be reported by discontinued CL wearers who experienced bad fit?

Discomfort/dry eye (they thought it was dry eye but it was really a fit/sag depth problem)

Why might low cyl not be Rxed in glasses of a CL wearer?

Easier switch between CL and glasses

When do you need to record the vertex distance on a myopic spec rx?

When there is noticeable change on vertex chart, or minification in glasses is substantial

Ways to measure vertex distance, best to worst

1. Distometer

2. Gauge on Trial Frame (less precise than distometer)

3. Phoropter (difficult to read, pt may not keep consistent distance during refraction)

Distometer Procedure

1. Trial frame

2. Binocular sphere check (flipper to adjust sphere)

3. Have pt close eyes

4. Measure VD with distometer, add 1mm for eyelid thickness (unless already added by manufacturer)

Reasons to choose daily disposables

• Lowest rate of overall complications

• Lowest level deposition

• Fewest unscheduled visits

• Great vision, sometimes improved comfort

Disadvantage of daily disposables

Cost

Why do many patients want EW?

They are bad at I&R…so we should help them with it so they don’t sleep in their lenses as much!

What must you give patients for which you prescribe extended wear?

Consent form