**Core Concept**
The question requires understanding of the anatomical structure of the retina, specifically the order in which light passes through the different layers. The retina is a complex neural tissue consisting of several layers, each with distinct cell types and functions. In the context of visual processing, it is essential to identify the correct layer through which light first enters the retina.

**Why the Correct Answer is Right**
Light entering the eye passes through the cornea, pupil, and lens before reaching the retina. Upon reaching the retina, light first encounters the retinal ganglion layer, which is the innermost layer of the retina. This layer consists of retinal ganglion cells, whose axons form the optic nerve and transmit visual information to the brain. The retinal ganglion layer is the first layer through which light passes due to its proximity to the vitreous humor, the gel-like substance filling the space between the lens and the retina. The retinal ganglion cells in this layer also play a crucial role in the transmission of visual signals to the brain.

**Why Each Wrong Option is Incorrect**
**Option A:** The inner nuclear layer is a deeper layer of the retina, containing the cell bodies of bipolar cells, Müller cells, and amacrine cells. It is not the first layer through which light passes.
**Option B:** The outer nuclear layer is a layer of the retina where photoreceptor cells (rods and cones) are located. These cells convert light into electrical signals, but they are not the first layer encountered by light.
**Option C:** The outer plexiform layer is a layer of the retina where synapses between photoreceptor cells and bipolar cells occur. It is a crucial layer for visual processing but is not the first layer through which light passes.
**Option D:** Although the retinal ganglion layer is the correct answer, it is worth noting that the term "ganglion layer" can sometimes be misleading, as it is not a single layer but rather a group of layers. However, in the context of this question, it is clear that the retinal ganglion layer is the correct answer.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the retina is a complex neural tissue, and the order in which light passes through its different layers is critical for visual processing. The retinal ganglion layer plays a crucial role in transmitting visual signals to the brain, and any damage to this layer can result in visual field defects or even blindness.

**✓ Correct Answer: D. Retinal ganglion layer**