Which factor affects the brightness of the Purkinje images observed?

The brightness of the Purkinje images, which are the reflections of the cornea and lens as seen during ophthalmoscopy or other optical examinations, is primarily influenced by the reflection properties of the surfaces involved.

Purkinje images are formed from the reflections off the anterior and posterior surfaces of the cornea and the lens, with the first image (P1) being the reflection off the anterior surface of the cornea, the second image (P2) from the posterior surface of the cornea, the third image (P3) from the anterior surface of the lens, and the fourth image (P4) from the posterior surface of the lens. The brightness of these images depends greatly on how much light is reflected off these surfaces, which is determined by their reflection properties.

For instance, a smoother surface will typically result in more specular reflection and therefore a brighter image, while a rough surface would scatter light more and yield a dimmer reflection. Additionally, the refractive indices of the materials involved (air, corneal tissue, aqueous humor, etc.) also contribute to the efficiency of the reflections, further affecting image brightness.

In contrast, corneal thickness, lens curvature, and optical density influence other aspects of ocular optics