Dispensing: Prescription analysis – Case #2

This case was among a series presented by Miranda Richardson FBDO, Assistant Director of Professional Examinations for the Association of British Dispensing Opticians, for peer discussion at the second Specsavers Dispensing Conference (SDC2) in August 2018.

Case #2

Habitual Rx:

Prescriber’s comments:

• VA: RE: 6/6 LE: 6/12

Looking at the above prescription, consider the following discussion points with your dispensing team:

• How would you describe this prescription?
• What is the relevance of the VA?
• What problems will this prescription cause? How much?
• How will this affect your lens selection?
• What optical solutions are available?

Discussion

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• This is a gross anisometropic prescription – a prescription with a difference of ≥2 D between the refractive errors of the right and left eyes.
• The patient is amblyopic. If the amblyopia is significant enough, the differential prismatic effect will be irrelevant and it may be possible to dispense a balance in the left eye.
• The patient may describe headaches, eye strain and / or double vision. Technically, they will be experiencing differential prismatic effect between the two eyes when they look down to read.
• They will experience approximately 3∆ base down in the left eye.
• For lens selection, consider the lens thickness between the right and left eye. Will aspherics make a difference with a minus lens? Would you use different indices between right and left lenses? Would you use iseikonic lenses?
• Optical solutions for differential prismatic effect include: slab-off, slab-on, separate pairs with lowered optical centre for near use, different bifocal segment sizes.

Possible recommendations:

• The amblyopia is small and the vision is useful in both eyes, meaning the correct prescription should be dispensed in both the right and left eyes.
• If the patient requires a multifocal, a slab-off progressive lens or a slab-off bifocal is possible. Both will have a visible line / seam all the way across the lens.
• Patients often prefer slab-off, which is applied to the most minus lens as the process involves making the lens thinner. Slab-on will make the most positive lens thicker, but in both instances the prism is equalled between the two eyes.
• Similarly, iseikonic lenses would mean making the right lens a similar thickness to the left lens. Patients usually prefer their lenses to be made thinner.
• If the patient prefers separate pairs, remember to drop the optical centres for the reading pair. This keeps the patient’s gaze through the optical centre and minimises the differential prismatic effect.

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More in the Prescription Analysis series
Case #1 and series introduction
Case #2
Case #3
Case #4
Case #5
Case #6
Case #7
Case #8