Quote from Dr. Garrett Smith on January 18, 2019, 7:31 pm

We've all been taught that we have to have Poison/"Vitamin A" to have good eyesight, night vision, avoid blindness, etc.

What if they were all wrong...and that we really NEEDED retinol binding protein (RBP) to PROTECT our eyes from the damaging effects of Poison/"Vitamin A"?

Let's jump into this one.  First, does Poison/"Vitamin A" damage the eyes?

Interphotoreceptor Retinoid-Binding Protein Mitigates Cellular Oxidative Stress and Mitochondrial Dysfunction Induced by All-trans-Retinal

Results: Content of atRAL [all-trans-retinal, aka Poison/"Vitamin A"] in Irbp^−/− [these mice genetically don't make interphotoreceptor retinoid-binding protein] retinal explants exposed to light for 40 minutes was significantly higher than that in wild-type retinas under the same light conditions. All-trans-retinal caused increase in cell death, tumor necrosis factor activation, and Adam17 upregulation in 661W cells. NADPH oxidase-1 (NOX1) upregulation, ROS generation, NO-mediated protein S-nitrosylation, and mitochondrial dysfunction were also observed in 661W cells treated with atRAL. These cytotoxic effects were significantly attenuated in the presence of IRBP.

Conclusions: Interphotoreceptor retinoid-binding protein is required for preventing accumulation of retinal atRAL, which causes inflammation, oxidative stress, and mitochondrial dysfunction of the cells.

Let's integrate what we just read above.  When there is a genetic LACK of retinol-binding protein in the eye (IRBP), an accumulation of atRAL (a form of Poison/"Vitamin A" happens, causing inflammation, oxidative stress, and mitochondrial dysfunction of the cells of the eye.

Another study talking about the "protective" effect of RBP against Poison/"Vitamin A":

Interphotoreceptor Retinoid-Binding Protein Protects Retinoids from Photodegradation

In view of the continual exposure of the retina to light, and the high oxidative stress in the outer retina, our results suggest IRBP may have an important protective role in the visual cycle by reducing photodegradation of all-trans and 11-cis retinols.

What would retinols degrade into?  They would degrade into retinoic acid(s), known in dermatology as a "chemical peel".  Your body would really rather not have a caustic chemical like that inside your eyeballs, so it makes RBP to protect itself.

What might we see in humans that are born with a genetic inability to make RBP then?  Might we see eye damage?  Let's have a look.  This is really important.

Phenotype in retinol deficiency due to a hereditary defect in retinol binding protein synthesis.

Abstract
PURPOSE: To describe the phenotype caused by a retinol deficiency in a family with compound heterozygous missense mutations (Ile41Asn and Gly75Asp) in the gene for serum retinol binding protein (RBP).

These two German girls didn't/don't make RBP due to a genetic defect.

METHODS: The two affected sisters, 17 (BR) and 13 (MR) years old, were examined clinically and with perimetry, color vision tests, dark adaptometry, rod- and cone-isolated electroretinograms (ERGs), multifocal ERGs, electrooculograms (EOGs), and laboratory tests.

That's a lot of exams!  If there are problems from missing RBP or other Poison/"Vitamin A" issues, I bet they'll find them.

RESULTS: There were no complaints besides night vision problems and no history of systemic disease. Visual acuity was reduced to 20/40 (BR) and 20/25 (MR). Anterior segments were normal except for a discrete iris coloboma. Both patients showed a typical "fundus xerophthalmicus," featuring a progressed atrophy of the retinal pigment epithelium. Dark adaptation thresholds were elevated. In the scotopic ERG, only reduced mixed responses were recordable. The photopic ERG was reduced in BR and normal in MR; implicit times were highly (BR) to slightly (MR) elevated. There was no (BR) to little (MR) light reaction in the EOG. All-trans retinol levels were 0.19 microM and 0.18 microM (normal range, 0.7-1.5 microM) for BR and MR, respectively, and did not increase in a dose-response test. RBP was below detection threshold, and retinyl esters were normal.

NO COMPLAINTS other than night vision issues.  Make sure to read below.  No RBP.  One-sixth (1/6) of normal serum retinol levels.  Acne (it seems now that RBP is important to acne prevention).

CONCLUSIONS: Both affected siblings had no detectable serum RBP, one sixth of normal retinol levels, and normal retinyl esters. The retinal pigment epithelium was severely affected, but besides acne there were no changes to other organs. This gives evidence for an alternative tissue source of vitamin A, presumably retinyl esters from chylomicron remnants. The normal retinol levels in the tear fluid explain the lack of xerophthalmia. However, considering the role of RBP in the tear fluid and, during development, in the yolk sac there is also evidence that there are organ-specific RBP forms not affected by the genetic defect.

I have a different explanation.  Humans make RBP to protect our eyes and our skin from the damage that Poison/"Vitamin A" causes.  Otherwise, it is not a vitamin and we don't need or want it.

One more bit of information on these two German girls, from another paper discussing them:

A case of human vitamin A deficiency caused by an inherited defect in retinol-binding protein without clinical symptoms except night blindness.

Two German siblings were found to suffer from night blindness and mild retinal dystrophy but no other clinical symptoms of vitamin A deficiency. Even though they had no detectable plasma retinal-binding protein (RBP) and their plasma retinol was exceedingly low, they showed normal physiologic functions and growth.

One-sixth of normal blood Vitamin A levels.  No "other" clinical symptoms of Vitamin A deficiency.  Totally normal physiologic functions and growth.  Are they special, or have we been misled on this so-called "vitamin"?

As I have mentioned elsewhere, protein malnutrition (dietary protein deficiency) has also been linked to night blindness.  Retinol binding "protein".  Does it make sense that if we don't eat enough protein, we can't make other proteins?