Illuminated Frenzel glasses are used in detecting
(Refer: AK Khurana Comprehensive Ophthalmology, 6th edition, pg no. 358 - 362)Illuminated Frenzel glasses (+20 lenses) are useful for abolishing fixation and thus revealing peripheral vestibular nystagmus
Nystagmus
Heterophoria
Esotropia
Astigmatism
Ocular motility and squint