高度軸性視差患者..knapp法則將會有所偏差.. - 眼鏡

Knapp法則

　　Knapp's Rule states that lenses placed at the anterior focal point of the

eye, generally 15 mm in front of the eye, will create similarly sized images

on the retina, whenever the disparity between the two eyes is due to a

difference in axial length of the eyes.



knapp法則說明當鏡片置於眼球的前焦點，通常在眼球前方15mm處，無論雙眼度數上

的差異為何，將會製造雙眼相同大小的眼底影像，原因在於雙眼眼軸長度之差異。




　　Knapp's rule, if the ametropia is entirely axial, corrective lenses

placed in the anterior focal plane of the eye will result in approximately

equal-size retinal image (iseikonia).



　　knapp法則，若屈光異常導因全是軸長因素，矯正鏡片置於眼球前焦點平面上將會

導致幾乎一樣大的眼底影像。



附註：物理模型說明對於純軸性遠視患者..由於鏡片形狀放大率效應將會導致法則失效。


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臨床檢測顯示對於近視高度視差患者，Knapp法則將會漸行失效，原因在於高度近視眼

球的視網網細胞密度會降低。




A study of aniseikonia and Knapp's law using a projection space eikonometer.

by P Kramer, S Shippman, G Bennett, D Meininger and V Lubkin



METHODS: Thirteen patients with suspected axial anisometropia of at least 4

Diopters were identified, selected and examined. Cycloplegic refraction,

A-scan ultrasonic ocular biometry and Essilor Projection Space Eikonometry

were performed.



RESULTS: Ten of the thirteen patients had their anisometropia

due primarily to ocular axial length differences. Of these ten, seven (70%)

had detectable levels of aniseikonia and 3 (30%) demonstrated no aniseikonia.

The other three patients whose aniso-metropia was due to combined axial and

refractive components, all had aniseikonia.




CONCLUSION: As a geometric optics theory, Knapp's Law stands on its own merits.

However, in clinical practice, reduction in retinal element density in high

myopia limits its applicability. Such patients often do have significant

aniseikonia which can produce ocular referable complaints and/or interfere with

binocular vision. | PMID: 10553112




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