7.1.7 Understands the special examination needs of patients with severe visual field defects

Types of severe VFD (4)

o Tunnel vision

o Wiped-out field

o Bitemporal hemianopia

o Homonymous hemianopia

Possible adaptations...

o Remove any potential obstacles

o Guide courteously

o Assist in finding patient's chair

o Use double slots for their appointments

o May not be able to find test chart

o May only read half of chart

o Appropriate targets (e.g., cover test)

o May find pinhole difficult

o Test slowly!

o Large changes in power of lenses

o Appropriate field test

How do you refract these px

o Patient set up (significant for patients with central vision loss):

- Maximise field of view in trial lenses:

§ Use trial frame and not phoropter head because trial frames have bigger aperture

than phoropter heads and the patient can move their head to get best vision.

§ Full aperture lenses to give wider field of view.

- Allow eccentric eye and head positions.

o Objective techniques are very important because the patient might not be able to see out

very well but we may be able to see in better:

- Retinoscopy

- 'radical retinoscopy' à method where you do anything you can to get a retinoscopy

reflex.

o Usually, it does not matter if retinoscopy result is not too accurate as you can refine with

subjective, however with LV patients it is better to use more time doing retinoscopy and

getting an accurate result.

Subjective changes - targets

o Use a target that can be seen!

- Which chart?

- Make target bigger/move chart closer - reduce testing distance to 3, 2, 1m

- Use CF, HM, PL, NPL

Sphere refinement

- Appropriate size of bracketing steps to VA à +/- 1-2DS/DC

- Initially even bigger if no ret. results

- Reduce bracket size as prescription is refined, but not too much.

Cyl refinement

o Cyl refinement:

- Round target of appropriate size

§ E.g., if patient's VA is worse than 6/12 then cannot use Verhoff ring therefore

improvise. Has to be a round target because needs to have all the meridians - would

use a bigger sized C or O.

§ Verhoff inner ring is 6/6 and outer ring is 6/12.

- Use high power cross-cyls (0.75 or 1.00DC)

PINHOLE - BE WARE (3)

o If cataract patient then pinhole would improve VA by miles as scattered light is limited but in

reality, cannot make vision that good.

o If glaucoma patient and only using central vision, adding a pinhole would limit vision!

o If macular degeneration patient using peripheral vision, adding pinhole blocks light out fully,

resulting in NLP.

Central VF loss (3)

Use Amsler chart as it best identifies areas of vision as well as defects.

- Can also use Amsler to help identify a potential preferred retinal locus (PRL).

- Suggest to patient that they should use their PRL to achieve best vision

Peripheral VF loss (2)

- Kinetic perimetry: Goldmann, Bjerrum - quickly indicates remaining field.

- Confrontation

Possible questions:

o How would you refract an AMD patient? Use larger steps to make it easier for the patient to

see the difference, but make changes in +/- 0.25DS steps.

o How would you adapt the test if a patient cannot get onto the slit lamp? Use direct

ophthalmoscopy.

o How would you measure visions/VAs for a patient with bitemporal hemianopia? Use the

central lines of the chart, i.e., central 2 lines.