Which of the following is NOT considered to be a major role of RPE cells? a. Phagocytosis of injured cells b. Formation of blood-retinal barrier c. Absorption of stray light d. Photopigment recycling e. Phagocytosis of outer segment discs

Retinal pigment epithelium (RPE) cells are essential for the proper functioning of the eye, particularly the retina. They are a layer of cells located between the sensory retina and the choroid. RPE cells perform a variety of crucial functions, such as providing nutrients to the photoreceptors, maintaining the blood-retinal barrier, and removing debris from the outer segment of the photoreceptors.

Now, let's analyze each option to determine which one is NOT a major role of RPE cells. a. Phagocytosis of injured cells: RPE cells are responsible for removing debris and waste from the photoreceptors, which includes the phagocytosis of dead or injured cells. This option is likely true. b. Formation of blood-retinal barrier: RPE cells help maintain the blood-retinal barrier, which is crucial for the proper functioning of the retina and preventing substances in the bloodstream from entering the retina. This option is also likely true. c. Absorption of stray light: RPE cells are pigmented, which allows them to absorb stray light and prevent it from scattering within the eye. This helps improve visual clarity. This option is also likely true. d. Photopigment recycling: RPE cells play a critical role in the visual cycle, which includes the regeneration of photopigments that are used in phototransduction. This option is likely true. e. Phagocytosis of outer segment discs: RPE cells are responsible for phagocytosing the outer segment discs of photoreceptors as part of their daily maintenance. This option is also likely true.

Based on the analysis of each option, it can be concluded that all the roles given are major roles of RPE cells. However, the question asks which of the roles is NOT considered a major role, in which case, option (a) Phagocytosis of injured cells could be considered the least significant role when compared to the others since the phagocytosis of outer segment discs (option e) is a more specific and essential function for the daily maintenance of photoreceptors. Thus, the correct answer is: a. Phagocytosis of injured cells