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1. Determination of the Best Spherical Glass
- Starting Point: Autorefractor values or old glasses values
- Give plus lenses and ask: “Does it get worse?”
- “No”: Continue giving plus lenses until vision worsens
- “Yes”: Give minus lenses until vision is “the same”, then give plus lenses again until vision worsens
- The last lens before vision worsens = best spherical glass
2. Cross-Cylinder Test 1: Axis Alignment
- Align the handle with the axis
- Rotate correction cylinder towards “better”
- Cave: Larger cylinders require more precise axis alignment!
3. Cross-Cylinder Test 2: Strength Alignment
- Align axis with axis
- If cylinder strength is increased, enhance sphere by half the cylinder’s strength (e.g., +1 cylinder dioptre –> +0.5 dioptre)
- If cylinder strength is decreased, reduce sphere by half the cylinder’s strength
4. Binocular Spherical Fine Adjustment
- Separate (polarization filter) by adjusting the two number rows (e.g., right eye sees the top row, left eye the bottom row)
- Fog with plus lenses; e.g., +0.5 or more, until both number rows appear grey/blurred
- Consider further fogging for the eye where the number row is blacker/sharper, until both appear equally grey
- Red-Green Test (= targeted defogging):
- Patient looks at the green background, then briefly at the red, and indicates where the black numbers appear blacker. Initially, it’s on the red background. Then “defog” (= give more minus) until the numbers on both backgrounds appear equally black
- Calculate test distance to infinity = add -0.25 dioptre.
Rules
- Full correction from school age
- In myopia, give as little minus dioptres as possible
- Red-Green Test: if green is sharper -> overcorrected
- In hyperopia, give as much plus dioptres as possible. Cycloplegia necessary. (Prescribe astigmatism values measured in miosis for glasses prescription)
- Red-Green Test: if green is sharper -> undercorrected
Prescribing Reading Glasses
- Reading glasses = Distance glasses + side-equal addition!
- Determining the relative accommodative range:
- Starting point: Distance glasses values. Use the near vision test chart at a standard distance of 40 cm. Patient looks at the vision line that is two rows below their maximum visual acuity (e.g., if distance vision is 1.25 -> patient looks at the 0.8 line of the near vision test chart)
- Add plus lenses (binocularly) –> vision first improves, then worsens. Patient indicates when vision starts to worsen = maximum addition (note this)
- Give weaker plus lenses until the first blur occurs = minimum addition (note this)
- Near addition = 1/2 x (max addition + min addition)
- Conversion formula depending on the distance for which the patient wants to use the glasses (e.g., for computer or TV glasses)
- Residual Accommodation + Addition (x dioptres) = 1/d
- If d = 80 cm –> 1/0.8 = 1.25
Children’s Glasses
Mittel- und Gegenständeliste (MiGel)
Liste des moyens et appareils (LiMA)
Elenco dei mezzi e degli apparecchi (EMAp)
Sources
- BAG – Mittel- und Gegenstandsliste (MiGel)
- Mittel- und Gegenständeliste (MiGeL) DE FR IT
- The Wills Eye Manual: Office and Emergency Room Diagnosis and Treatment of Eye Disease; Nika Bagheri MD, Brynn Wajda MD, et al; Lippincott Williams&Wilkins; 7th Edition (2016)
- Kanski’s Clinical Ophthalmology: A Systematic Approach; Jack J. Kanski MD, Brad Bowling MD; Saunders Ltd.; 8th Edition (2015)