Refractor Head

  • Time-saving refracting device with self contained lenses in discs that revolve in front of each eye
    • contains all lenses & accessories found in trial case with separate discs for:
      • spheres, cyls (EITHER plus or minus – NEVER BOTH), accessories (optional)
    • also self-centering cross-cylinders, rotating prisms & Maddox rod (they all line themselves up with optical centre of lens when clicked into place)
    • attachment for holding near-point targets
  • Disadvantages
    • Limited FOV from telescope effect (minimum of 30mm tube thickness) so less ‘natural’ vision (tunnel vision)
    • Unable to see px’s face
    • Px’s head must remain still to remain centred (cyls & prisms)
    • Difficult if abnormal head posture
    • Reading tests with eyes in primary position only
    • Occasional temptation to twirl lenses faster than px’s ability to respond (easier to twirl lenses on RH than replace lenses on trial frame)
    • If not sealed unit lenses become smudged & need expensive cleaning
    • More prone to steaming up & collecting make-up
    • Maximum cyl power is limited & usually only minus
    • Lacks portability
  • Advantages
    • Many lens choices & variations – e.g. can maintain spherical equivalents (????) & rotary prisms can enable equal & symmetrical prism adjustment
    • Very convenient in terms of speed
    • No weight on px’s nose
    • Optical BVD device on newer models
  • Modern digital phoropters/refractor heads = more automated than manual design; control box; added sophistication & cost
    • Small, compact design, lightweight, easy & comfortable to operate with multifunctional button, pre-programmed routine stages, fast entry & adoption of measuring values without transfer errors, data transfer between different instruments & office management programmes, controls chart projector (Rodenstock model)
  • Clear RH before starting of any prescription/other lenses etc, carry out prelims (visions, PD, CT), set PD on RH then level with px
  • Auxiliary lens dial = main lens dial with 12 settings
  • There are two sphere dials – one weak sphere dial (0.25D steps) & one strong sphere dial (3.00D steps on auxiliary dial)
  • Cyl power = inner control, cyl axis = outer control
  • Cross cyl unit – ‘P’ = power meridian, turn unit by 45° to check axis (make sure axis of CC coincides with correcting axis)
  • Rotary (Risley) prism unit – arrow head indicates prism strength & base direction
  • Controls used in retinoscopy:
    • Ret lens (+1.50 DS) NOT recommended (?????)
    • Main sphere control – pull down to add plus lens, push up to add minus lens (0.25DS)
    • Auxiliary sphere control +/-3.00DS steps
    • Move through astigmatic focus (astigmatic pencil) to check astigmatic interval with spheres
    • Then insert –ive CYL at correct axis when neutralised most +ive sphere meridian
    • Add –ive working distance lenses to ret result for each eye
    • Record D.V. acuity
  • Controls in X-Cylinder (cross-cyl):
    • If ret VA better than 6/12, sphere control to equalise bichromatic (duochrome) test before X-cyl
    • Directing px to Verhoff Circles twirl X-cyl in axis checking. Adjust axes if required by at least 20° in cyls <1.00DC (smaller cyls have less specific axis so better to start off by bracketing large and then narrowing down gradually). Bracket until equal blur
    • Then adjust power. For every -0.50DC change, adjust sphere control by +0.25DS – important in presbyopes as they have low accommodation anyway, too much minus would push focal point too far back & they would not be able to compensate with accomm. that they don’t have, so vision would always be blurred. Important for younger px’s too as their active accommodation will affect the final Rx result
  • Controls in balancing:
    • Both TIB & Humphriss Technique push plus i.e. acuity in the eye under test has to blur with extra +0.25DS (so if px can still see same line of letters then give +0.25DS but only stop giving when it blurs with EXTRA +0.25DS)
    • If adding -ive sphere acuity should increase by a line of Snellen letters
    • Try binocular ADD +0.25DS (both eyes simultaneously) after TIB or Humphriss
  • Controls for Maddox Rod
    • Using auxiliary lens wheel dial up Maddox Rod Horizontal
    • Ask px to fixate on D.V. spot light & indicate position of streak image R or L
    • Put Risley prism in place & move streak image in RE using Base IN prism for EXO, Base OUT for ESO deviations
    • Repeat using Maddox Rod Vertical (MRV) & Risley Prisms
    • Start settings 12 Base IN (R) & WMH (L)
  • Amplitude Measure
    • Use small ‘nonsense’ print on near card
    • Remember amplitude rule is 66cm (1.50D)
    • Presbyopic +2.00DS temporary additions will blur near acuity targets at 66cm’s (blur?!?!)
    • In pre-presbyopes use at least -4.00DS
  • Dynamic X-cyl
    • Used to check reading adds with grid target in presbyopes
    • 50 X-cyl with –ive axis at 90°
    • Vertical lines of grid are posterior, H lines anterior
    • H & V grid lines equally clear if add correct
    • If over-plussed vertical lines clearer
    • If over-minussed horizontal lines clearer

  • Near phoria prism dissociation (measuring fusional reserves)
    • Auxiliary prisms are often used to dissociate the eyes in preference to Risley prisms but these will be for set strengths & directions
    • Do near vertical phoria fusion first using horizontal line of letters (measurement of vert. fusional reserve using hoz. single line target). Use 6 Base DN vertical prism in front of RE to produce vertical diplopia of horizontal single line target. Ask px whether upper letter target appears to right or left of lower target (directions of line = same for exo & eso). Use Risley prisms base in/out to align letter targets
    • Then do near horizontal phoria fusion using vertical line of letters (measurement of hoz. fusional reserve using vert. single line target). Use 10 Base IN horizontal prism in front of RE to produce horizontal diplopia of single vertical line target. Ask px whether vertical letter target appears level. Use Risley prisms base up/down to align letter targets
  • NRA & PRA (negative relative accommodation & positive relative accommodation)
    • Positive relative accommodation is measured using a near single line acuity (6/6) target by adding minus lenses until blur indicated (-2.50DS)
    • Negative relative accommodation uses the same target with plus lenses until blur indicated (+2.50DS)

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