The neural retina occasionally detaches from the pigment epithelium. In some instances, the cause of such detachment is injury to the eyeball that allows fluid or blood to collect between the neural retina and the pigment epithelium. Detachment is occasionally caused by contracture of fine collagenous fibrils in the vitreous humor, which pull areas of the retina toward the interior of the globe. Night blindness: Night blindness occurs in any person with severe vitamin A deficiency. The reason for this is that without vitamin A, the amounts of retinal and rhodopsin that can be formed are severely depressed. This condition is called night blindness because the amount of light available at night is too little to permit adequate vision in vitamin A–deficient persons.In addition, the retina has been described as a "window" into the brain and body, given that abnormalities detected through an examination of the retina can discover both neurological and systemic diseases. Diagnosis
A number of different instruments are available for the diagnosis of diseases and disorders affecting the retina. Ophthalmoscopy and fundus photography have long been used to examine the retina. Recently, adaptive optics has been used to image individual rods and cones in the living human retina, and a company based in Scotland has engineered technology that allows physicians to observe the complete retina without any discomfort to patients.The electroretinogram is used to non-invasively measure the retinas electrical activity, which is affected by certain diseases. A relatively new technology, now becoming widely available, is optical coherence tomography (OCT).
Layers imagable with optical coherence tomography
Using optical coherence tomography (OCT) there are 18 layers that can be identified in the retina. The layers and anatomical correlation are as follows:

From innermost to outermost, the layers identifiable by OCT are as follows:

Development
Retinal development begins with the establishment of the eye fields mediated by the SHH and SIX3 proteins, with subsequent development of the optic vesicles regulated by the PAX6 and LHX2 proteins. The role of Pax6 in eye development was elegantly demonstrated by Walter Gehring and colleagues, who showed that ectopic expression of Pax6 can lead to eye formation on Drosophila antennae, wings, and legs. The optic vesicle gives rise to three structures: the neural retina, the retinal pigmented epithelium, and the optic stalk. The neural retina contains the retinal progenitor cells (RPCs) that give rise to the seven cell types of the retina. Differentiation begins with the retinal ganglion cells and concludes with production of the Muller glia. Although each cell type differentiates from the RPCs in a sequential order, there is considerable overlap in the timing of when individual cell types differentiate. The cues that determine a RPC daughter cell fate are coded by multiple transcription factor families including the bHLH and homeodomain factors.In addition to guiding cell fate determination, cues exist in the retina to determine the dorsal-ventral (D-V) and nasal-temporal (N-T) axes. The D-V axis is established by a ventral to dorsal gradient of VAX2, whereas the N-T axis is coordinated by expression of the forkhead transcription factors FOXD1 and FOXG1.