Principles and Technique of Fogging During Subjective Refraction

Excerpt

Fogging refers to using plus powers to bring the optical point of focus in front of the retina and into the vitreous, ensuring that accommodation is adequately relaxed. Accommodation is the ability of the eye to change its total dioptric power to bring objects at different distances into focus.

This ability has been demonstrated in vivo and in vitro. The stimulus to accommodation is a retinal blur. When the eye focuses on a near object, a triad of processes occur, including miosis, convergence, and accommodation.

The principle of fogging involves using spherical powers to create artificial myopia, thereby moving the entire area of focus in front of the retina and creating a situation where an attempt at accommodating will blur the vision, inducing further relaxation of accommodation. Fogging is effective irrespective of the inherent refractive state of the eye.

Proper accommodation control is possibly the most critical factor in the refraction process. The refraction endpoint will fluctuate without proper accommodation control, leading to incorrect spectacle prescriptions.

This activity details the principles and techniques of the fogging process.