Maintenance of ophthalmic equipment and instruments

The maintenance of ophthalmic equipment and instruments often becomes the responsibility of one person in the office. Someone may be more technically adept to take on this responsibility. Simplified instructions on care and maintenance are noted in the following text.

It is important that adequate supplies of replacement bulbs be maintained and that everyone be familiar with the different bulbs required for each of the available pieces of equipment. Lists of the required bulb for each piece of equipment should be made and posted. If batteries are required, a suitable battery supply should also be maintained. If the batteries are the rechargeable type, they should be charged fully the first time. They can be recharged to the same full capacity on each recharging, which should take place on a regular basis. Handles usually contain rechargeable batteries that require nightly recharging in a battery well. All equipment should be kept covered with dust covers supplied by the manufacturer.

Applanation tonometer

Calibration of the applanation tonometer is important, and it should be checked approximately every 2 months or sooner with regular use. Tonometers are always supplied with a calibration bar. The most common applanation tonometer is the Goldmann tonometer. Applanation tonometers may be checked for accuracy by the use of a central weight. For the Goldmann tonometer, a short rod of measured weight is attached to the balancing arm of the tonometer and the rod set at 0, 2, and 6. At each measure, the measuring drum should be placed at the corresponding stop. At each stop, the tonometer head should move only 0.05 to 0.1 g of these settings ( Fig. 11.1 ).

Fig. 11.1

Calibration bar for Goldmann applanation tonometer.

To be specific, follow these guidelines:

  • 1.

    To check at drum position zero (0), insert the measuring prism at measuring position − 0.05. The zero mark on the measuring drum is set one line width below the index. When the pressure arm, with prism in position, is gently pushed, it should move freely between the two stops and return toward the stop on the examiner’s side ( Fig. 11.2 ). At measuring position + 0.05, the zero mark on the measuring drum is set one line width above the index. As this procedure is followed, the pressure arm should move toward the patient’s side.

    Fig. 11.2

    Calibrating Goldmann applanation tonometer at position 2. The tonometer head should move only 0.05 to 0.1 g from zero.

  • 2.

    Check at drum position 2. For this check the control weight is used. Five circles are engraved on the weight bar. The middle one corresponds to drum position zero, the two immediately to the left and right are position 2, and the outer ones are position 6. One of the marks on the weight corresponding to drum position 2 is set precisely on the index mark of the weight holder. Holder and weight are then fitted over the axis of the tonometer so that the longer part of the weight points toward the examiner ( Fig. 11.3 ).

    Fig. 11.3

    Calibration with larger weight toward the examiner. Balance should show scale variation no greater than zero.

  • 3.

    At drum positions 1.95 and 2.05 (graduation mark 2 on measuring drum set one line width below or above the index), the pressure arm should return from the area of free movement to the corresponding stop.

  • 4.

    The check at drum position 2 is the most important and should be carried out frequently because the measurement of intraocular pressure in this range is of particular importance.

  • 5.

    Check at drum position 6 in the same manner. The corresponding checking points are 5.9 and 6.1. The graduation mark 6 on the drum is offset by half an interval below or above the index.

The applanation tonometer consists of a plastic prism with a flat anterior surface and a diameter of 7 mm. This prism is brought into contact with a fluorescein-stained tear film of the cornea, which it displaces to the periphery of the contact zone until a surface of known and constant size of 3.06 mm is flattened. The inner border of the ring represents the line of demarcation between the cornea flattened by applanation and the cornea not flattened. The measuring drum can regulate the tension to produce a force between 0 and 8 g.

Noncontact tonometer

Calibration of the noncontact tonometer is important. The use of the logic circuits in the instrument, which are necessary to measure and record intraocular pressure, enables the operator to check the calibration of the pneumatic-electronic network by the following procedure:

  • 1.

    Turn the instrument to on (red dot).

  • 2.

    Remove the objective cap and wait 30 seconds for warm-up.

  • 3.

    Depress the trigger switch-display at 68.

  • 4.

    Push the power switch knob and set it at D.

  • 5.

    Depress the trigger switch-display at 47 + 1.

Triggering is repeated several times 8 to 10 seconds apart. The display must not change more than +1 count. There must be no source light indicator (SLI) light in any of the tests. During the check of calibration, the display number has no quantitative significance; its repeatability must be the concern. The number displayed is a specially selected equivalent to a critical check at approximately 20 mm Hg, with twice the resolution that is used in the actual intraocular pressure (IOP) measurement.

The noncontact tonometer is sturdily constructed and normally requires little care to keep it operationally perfect. Protecting the equipment against dust is important to maintain it in good working order. It is recommended that the supplied dust covers be used.

Bulb replacement

Target illuminator bulb

  • 1.

    Always disconnect the instrument from its source of electrical power.

    Remove the instrument top by unscrewing two screws with a <SPAN role=presentation tabIndex=0 id=MathJax-Element-1-Frame class=MathJax style="POSITION: relative" data-mathml='332′>332332
    3 32
    hex wrench.

    Free the bulb holder by loosening the set screw, marked B, with a <SPAN role=presentation tabIndex=0 id=MathJax-Element-2-Frame class=MathJax style="POSITION: relative" data-mathml='116′>116116
    1 16
    hex wrench.

  • 2.

    Pull out the bulb holder.

  • 3.

    Remove the bulb by unscrewing the knurled retainer ring.

  • 4.

    Replace the bulb with a no. 12419 bulb and wipe the bulb clean of fingerprints.

  • 5.

    To adjust for maximum and even target illumination, view the red-dot target through the objective orifice and adjust the bulb holder on axis with the power on. Tighten the set screw.

  • 6.

    Replace and secure the instrument cover to protect against dust.

Source light indicator

If replacement is ever necessary, it should be made only by a qualified service technician. An authorized American Optical distributor should be contacted.

Fixation lamp

To replace the fixation bulb, the center joint is separated by pulling apart. The screw base bulb (no. 11583) is exposed for replacement.

Chin rest

The chin rest is easily removed by twisting it 90 degrees, then pulling up. It is made of a durable material that can be sterilized (maximum 250°F [121°C]) or washed in soap and water or alcohol.

Paper chin rests also are available.

Headrest cushions

Headrest cushions are wiped clean with alcohol. They also may be replaced.

Eyepiece and objective

  • 1.

    The exposed surfaces of the eyepiece and objective should be kept free of dust, fingerprints, and smudges. The lens surfaces should be dusted occasionally with a camelhair brush.

  • 2.

    The alignment target, as viewed by the operator, may become blurred by accumulation of grease from eyelashes on the annular aperture of the objective. Clean the annulus with a dry cotton-tipped stick.

  • 3.

    After prolonged service or use in a dusty or humid environment, the inside surface of the objective should be cleaned. Remove the objective by unscrewing it counterclockwise and dust the surface with a brush or, if necessary, wipe it clean with a dampened tissue paper before reassembly.


The lensmeter requires little maintenance. The eyepiece should always be adjusted for each technician using this instrument. Operators should focus or adjust the eyepiece to their eye.

If the lensmeter has a prism compensator, which is located just under the eyepiece, the compensator should always be set on zero to ensure you obtain the correct reading. (For further details, see Ch. 8 .)


We shall use the Bausch & Lomb keratometer as an example.

  • 1.

    When not in use, or at least overnight, the keratometer should be kept covered with the dust cover supplied with the instrument. Dirt on the daylight-blue filter sometimes causes smudges in the mire imagery. The filter can be removed easily and cleaned by removing the two screws that hold the lamp housing to the body of the instrument.

  • 2.

    When carbon deposits begin to form on the lamp bulb, the mire imagery will be diminished. If this occurs, a new bulb should be used in the instrument.

  • 3.

    The lower part of the lamp housing is removed easily for the insertion of a new bulb. To replace the bulb, rotate the instrument by turning the set until the lamp housing is away from the central carriage. The base can be removed by loosening the two screws on the sides of the lamp housing. In replacing the base, one must take care to see that the base rests squarely on the shoulder of the housing; otherwise that part will not clear the carriage when it is rotated back into position.

  • 4.

    There is also an attachment that can be used for checking keratometer measurements. This attachment comes complete with bracket and three test ball bearings with specific radii. To calibrate, use a spherical test ball of known radius of curvature inserted in a holder. When the correct radius of curvature of the test ball is obtained, the accuracy of the keratometer can be confirmed. If the keratometer is out of alignment, it should be repaired by a trained professional.

Slit-lamp biomicroscope

  • 1.

    The slit lamp is an important instrument. All personnel who use it should make a habit of keeping it covered with a dust cover when it is not in use. When changing bulbs, be sure the instrument is unplugged. Also, always remember to wipe off all fingerprints on the bulb to extend its life.

  • 2.

    If the slit lamp will not operate, replace bulbs even if they appear to be in good condition. If the slit lamp does not light when a new main bulb is installed, check contacts on the bulb cap and remove any dirt with a small file or knife. If the instrument still does not operate, check all electrical connections to make sure that all wires are plugged into the transformer and that the main power cord is plugged in. Also check for a faulty fuse in the transformer.

  • 3.

    The Haag-Streit and copies are the only slit lamps with mirrors that require cleaning. Removal of the mirror is easiest when the microscope and illuminator are well separated and the latter is inclined by approximately 10 degrees or more. Grasp the narrow shank of the long mirror and pull upward. The small mirror, which has no shank, is more difficult to grasp; therefore the point of a pencil should be used to get the mirror started on its way out. The mirror should then be dusted and sprayed with a glass cleaner. Wipe clean with cotton balls or some other material that will not scratch the surface, using a downward stroke. Repeat until dry.

  • 4.

    If the slit lamp becomes difficult to move with the joystick, clean the joystick pad with a cleaning solution. If slit-lamp movement still continues to be difficult, apply a thin coat of three-in-one oil or sewing machine oil to the pad.

Phoropter ( Fig. 11.4 )

All personnel should make it a habit to keep the phoropter protected with a dust cover when not in use. Alcohol should not be used on any part of the phoropter.

  • 1.

    The semipermanent face shields furnished with the phoropter are made of white nylon. This material can be washed with soap and water, soaked in alcohol, or boiled in water.

  • 2.

    All lenses should be kept clean and free of dust and fingerprints. Do not put a finger in the sight aperture to check lens placement. Fingerprints on the lenses make refraction difficult. Cleaning of dust on enclosed lenses can be done with an ear syringe. The back lenses are the retinoscopy lens, polarizing lens, red lens, and Maddox rod. These are the only lenses that may be cleaned by office personnel; a glass cleaner and cotton-tipped swabs are used. The phoropter should be sent to an authorized repair shop every 2 years for preventive maintenance and lens cleaning.

  • 3.

    Because the cross cylinder and the rotary prism are not enclosed, it is advisable occasionally to wipe each one carefully with lens tissue to remove dust.

Jun 26, 2022 | Posted by in OPHTHALMOLOGY | Comments Off on Maintenance of ophthalmic equipment and instruments

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