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J M Enoch

Publications and source records attributed to J M Enoch.

170 records · Page 10Linked to original sources
PubMedDate not supplied

Refractive astigmatism acts predominantly as a source of high spatial frequency image distortion: the associated lineal distortions can be overcome by using a low pass spatial filter!

PURPOSE: Surprisingly, an important characteristic of astigmatism has been overlooked by ophthalmic and clinical scientists. Apparently, refractive astigmatism is due largely to a form of high spatial frequency image distortion. METHODS: Characteristic astigmatic image distortion can be minimized or eliminated by using a low-pass spatial filter (here, a ground glass plate was employed for this purpose). The ground glass is placed a short distance in front of a visual acuity chart, or it may be used with other tests, such as vernier acuity. RESULTS: This test has been performed by us on large numbers of patients and test subjects. A clinician can try this test for himself/herself. Place a +2.00 D.C. (any axis) lens in front of the eye; the usual distortions will be observed. Locate the ground glass plate as described. The usual distortions associated with the conoid of Stürm will not be visible or will be virtually eliminated, although some image blur will remain. CONCLUSIONS: This technique has significance, e.g., in visual screening programs in developing nations, or in assessing patients with media disorders prior to ophthalmic surgery.

Astigmatism↗
PubMedDate not supplied

Virtual image of the incus from a saline lens: an aid to safe dissection of the mastoid antrum.

Dissection of the antrum requires judicious visualization of the tegmen, horizontal canal, incus, and facial nerve. Inadvertent contact with the incus by the power drill may cause significant acoustic trauma. An effective "early warning device" accurately predicting exposure of the incus may be constructed with the saline irrigation fluid. The formation of the meniscus at the antrum permits visualization of the image of the incus around the corner of the bony canal wall overhang. A thin-lens model of this phenomenon has been created for first-order analysis of the optics, and it provides useful criteria for using this image. Image minification, displacement, and distortion were analyzed. A more complex model was then created to assess the impact of changing meniscus shape. The latter helped in understanding an added "swinging-door effect" noted as the meniscus was altered. The model predicted accurately the phenomena as observed in the temporal bone preparation. Illustrative examples of the optics and photographic demonstrations of the phenomena are presented.

Dissection↗
PubMedDate not supplied

Amount of aniseikonia compatible with fine binocular vision: some old and new concepts.

Random Dot Stereograms (RDS) are useful, but are sometimes misleading in assessing the degree of binocular cooperation in the presence of aniseikonia. RDS may give positive results up to 15% aniseikonia, whereas a fine central binocularity is not possible with more than 5% image-size difference. It is suggested that stereopsis may not be the only parameter to test; stress is given to the importance of peripheral motor fusion in maintaining the eye alignment.

Amblyopia↗
PubMedDate not supplied

Management of aniseikonia after intraocular lens implantation or refractive surgery.

BACKGROUND: Aniseikonia is a difference in perceived image size in the two eyes resulting in asthenopic symptoms and distortions of binocular space perception. This is a complication of refractive and implant surgery in patients with binocular vision. While many individuals adapt readily to modest aniseikonic errors, quite a number do not. METHOD AND RESULTS: Few instruments exist to adequately test for aniseikonia. A means is described to determine if aniseikonia exists and a series of simple steps is suggested to minimize aniseikonia induced by refractive surgery or by surgery for removal of cataract and intraocular lens insertion. Also, using the proposed protocol, it is possible to determine if existing image size differences resulting from prior and/or induced aniseikonia are predominantly refractive or axial. A case report is presented. CONCLUSIONS: The techniques described are not costly, provide no risk, take little time, and resolve or meaningfully reduce aniseikonia in many patients having non-extreme errors of this type.

Aniseikonia↗