|Year : 2020 | Volume
| Issue : 7 | Page : 1452
The bifocal scotoma
Amber A Bhayana, Vinit Tanwar
Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India
|Date of Web Publication||25-Jun-2020|
Dr. Amber A Bhayana
Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, Ansari Nagar, New Delhi - 110 029
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Bhayana AA, Tanwar V. The bifocal scotoma. Indian J Ophthalmol 2020;68:1452
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, 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.
|Figure 1: (a) Light across bifocal glasses showing the scotomatous area (white arrow). (b) Ray diagram explaining the mechanism for the same|
Click here to view
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
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.
Mamalis N. Negative dysphotopsia following cataract surgery. J Cataract Refract Surg 2010;36:371-2.