Visionstar JS-68

The datasheet calls it a trial lens set and states no specific use. Its composition of spheres in both signs and twelve minus cylinders, with no prisms or accessories, matches what is widely sold as a perimeter lens set: lenses that correct the patient's refractive error in the lens holder of a visual field analyser. It can also serve quick refraction checks away from the main clinic. Before ordering for perimetry, confirm that the lenses fit your analyser's holder.

Uncorrected refractive error lowers measured sensitivity and can make a visual field look worse than it is. A study on the Humphrey Field Analyser found a mean fall of 0.89 dB per dioptre of uncorrected distance myopia and 0.63 dB per dioptre of induced hyperopia across the tested points. An earlier study with Octopus perimetry found that the emmetropic condition gave the highest central sensitivity in 21 of 22 eyes. In glaucoma follow-up, where small changes in sensitivity inform treatment decisions, a correctly chosen lens removes one avoidable source of error.

That cannot be confirmed from the datasheet, which gives neither the lens diameter nor the rim thickness. Perimeter lens holders accept a specific lens size, and a lens that sits loose or at the wrong distance from the eye can cause rim artefacts in the peripheral field. Ask the seller for the outer diameter and rim thickness, and check them against the holder specification in your analyser's manual before order.

The feature list states 68 pieces, twelve of them minus cylinders, which implies 56 spheres: one of each of 28 powers in each sign. The table's quantity column shows 2 against each sphere power, which would give 112 spheres and 124 pieces in total. The stated total and the cylinder count point to one of each, which is how 68-piece sets are normally composed, but the table disagrees. Ask the seller to confirm the packing list in writing.

Spheres run from 0.25 D to 16.00 D in both signs: 0.25 D steps to 3.00 D, 0.50 D steps to 7.00 D, 1.00 D steps to 14.00 D, then 16.00 D. There is no 0.12, 3.25, 3.75, 7.50, 15.00 or 18.00 D and above sphere. Minus cylinders run 0.25 to 1.00 D in quarter steps, then 1.50 to 5.00 D in half steps, so 1.25, 1.75, 2.25, 2.75, 3.25 and 3.75 D are absent. For perimetry, where the correction is usually rounded to the nearest available lens, those steps are generally adequate.

There are no plus cylinders, so a prescription written in plus-cylinder form must be transposed to minus-cylinder form before use. There are no Maddox rods, prisms, cross cylinders, filters, occluder, pinhole or slit, and no trial frame. Each sphere power appears to be supplied once per sign, subject to the count question above. Those absences are consistent with a correction set, but they rule out full subjective refraction from this case alone.

Only for simple checks. Without cross cylinders, the practitioner cannot refine cylinder axis and power in the usual way. With single lenses rather than pairs, both eyes cannot hold the same power at once for binocular balancing, and there is no occluder for monocular testing. A practitioner could confirm an existing prescription at a care home or satellite clinic, but the set is not built to derive a new one.

A lens placed in a perimeter holder or trial frame may face either way, and in a dim perimetry room the operator needs to read its power without turning it. Engraving on both sides of the rim makes the power legible from either face, and cut marks suit repeated handling and cleaning. The datasheet does not say how cylinder axes are marked, so check each cylinder on a focimeter at delivery.

Visual field testing is often delegated to trained assistants or technicians. In its 2026 consultation on the testing of sight statement, the General Optical Council's stated view is that optometrists or registered medical practitioners may delegate tasks such as visual fields to a suitably trained person, provided they retain overall control. Subjective refraction for prescribing remains with registered optometrists and medical practitioners under the Opticians Act 1989. Other countries set their own rules.

The reference product standard is BS EN ISO 9801:2009 for trial case lenses, confirmed by ISO in 2024. The datasheet claims no conformity, so ask for test evidence. Under UK MDR 2002 the set is typically Class I, or higher, use-dependent, confirmed against the declaration of conformity at order. The declaration is issued by the manufacturer and provided by the seller. Conformity requirements differ by destination market, and the seller confirms what applies where the unit is going.

The set has no electrical parts, so it falls outside electrical safety and portable appliance testing, and in a UK workplace PUWER 1998 applies as it does to any work equipment. Lenses in a perimeter holder sit close to the patient's face, so cleaning between patients matters. Disinfectant compatibility for the lenses, rims and engraving is not published, so ask for the manufacturer's cleaning instructions and single-lens replacement pricing.

A practice looking for a full refraction set will find no cross cylinders, pairs, prisms or accessories. A clinic whose prescriptions are written in plus-cylinder form will need to transpose every time. A service whose analyser holder takes a specific lens size should not order until the diameter is confirmed.