Stereoscopic treatment of heterophobia and heterotropia : designed to accompany the phoro-optometer stereoscope and the Wells selection of stereoscopic charts / by David W. Wells.

  • Wells, David W.
Date:
1912
Catalogue details

Licence: In copyright

Credit: Stereoscopic treatment of heterophobia and heterotropia : designed to accompany the phoro-optometer stereoscope and the Wells selection of stereoscopic charts / by David W. Wells. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    DUCTION. Whether the case be one of orthophoria or heterophoria it is important to know the strength of the recti muscles, as many ortho- phoric patients have such weak muscles that they are Unable to do continuous work without asthenopia or nervous disturbance. Normal accommodation means that each eye shall be able to focus an object as near as 8 to 10 cm. If the pupillary distance be 60 mm., convergence to this distance requires 60A. If the average reading distance be taken as 30 cm., 20A would be used. As the comfortable maintenance of accommo- dation at 30 cm. requires an ability to accommo- date at 10 cm., so the convergence faculty must be much greater than the amount habitually used. Cross,* of Worcester, Mass., ''believes that if the fusion range is not at least twenty per cent, in excess, there are apt to be more or less asthenopic symptoms.'' Landoltf says, We have tried to determine the quota of convergence, and our experience *Personal communication. f'Norris and Oliver System of Eye Diseases, Vol. IV, p. 133.