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   Table of Contents      
OPHTHALMIC IMAGE
Year : 2020  |  Volume : 68  |  Issue : 7  |  Page : 1452

The bifocal scotoma


Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India

Date of Web Publication25-Jun-2020

Correspondence Address:
Dr. Amber A Bhayana
Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, Ansari Nagar, New Delhi - 110 029
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijo.IJO_26_20

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How to cite this article:
Bhayana AA, Tanwar V. The bifocal scotoma. Indian J Ophthalmol 2020;68:1452

How to cite this URL:
Bhayana AA, Tanwar V. The bifocal scotoma. Indian J Ophthalmol [serial online] 2020 [cited 2020 Jul 13];68:1452. Available from: http://www.ijo.in/text.asp?2020/68/7/1452/287557



An ellipse of the dark area is always seen whenever the light is allowed to pass through bifocal glasses [[Figure 1]a- white arrow]. This ellipse corresponds to the junction of the distant and near lenses and we believe it to cause some form of scotoma to the person whose mechanism [Figure 1]b we hypothesize to be very similar to roving ring scotoma,[1] in case of aphakic glasses. Differential refraction, causing differential prismatic deflection, at the junction of 2 optically dissimilar surfaces forms a scotoma between the 2 zones as shown. The same mechanism partly also contributes to negative dysphotopsias.[2]
Figure 1: (a) Light across bifocal glasses showing the scotomatous area (white arrow). (b) Ray diagram explaining the mechanism for the same

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There are no conflicts of interest.



 
  References Top

1.
Welsh RC. The roving ring scotoma with its jack-in-the-box phenomenon of strong-plus (aphakic) spectacle lenses. Am J Ophthalmol 1961;51:1277-81.  Back to cited text no. 1
    
2.
Mamalis N. Negative dysphotopsia following cataract surgery. J Cataract Refract Surg 2010;36:371-2.  Back to cited text no. 2
    


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