Retinoic acid plays an important role in ocular surface health and wound healing. It promotes epithelial cell differentiation and hydration of the ocular surface. Retinoic acid also accelerates wound healing in corneal epithelium and full thickness wounds. However, high concentrations can inhibit wound healing and cause meibomian gland dysfunction by decreasing oil secretion. Retinoic acid reverses squamous metaplasia and has anti-tumor effects on the ocular surface at appropriate concentrations.

1. Retinoic acid and the ocular surface
CHAMEEN SAMARAWICKRAMA, BSC(MED), MBBS, PHD,
SKY CHEW, BSC(MED), MBBS, PHD
STEPHANIE WATSON, BSC(MED), MBBS, PHD, FRANZCO
Surv Ophthalmol. 2015 May-Jun;60(3):183-95
Sydney Eye Hospital, Sydney, New South Wales, Australia; Save Sight Institute, University of Sydney, Sydney,
New South Wales, Australia.

2. Introduction
 Vit A has been known to improve cutaneous wound healing.
 It accelerates epithelial migration, granulation tissue formation and
reversal of the retardation of healing induced by corticosteroids
 This review explores the international literature on ophthalmic use of
retinoic acid on the ocular surface.

3. Vitamin a deficiency
 Leading cause of childhood blindness in developing countries
Manifests in 2 ways:
 Night blindness/nyctalopia
 Xerophthalmia
Ocular changes include..
 Epidermal keratinization
 Squamous metaplasia
 Corneal ulceration
 Night blindness
 Retinopathy

4. Vitamin a deficiency
 Initial and most common ocular manifestation of vitamin A
deficiency is nyctalopia.
 Retinal electrophysiology can assist in diagnosis and follow up of
vitamin deficiency

5. Vitamin A deficiency
 Conjunctival pathology typically follows nyctalopia.
 First sign is xerosis (dryness)
 Conjunctiva appears thickened, wrinkled with loss of transparency.
 Bitot spots- triangular, perilimbal foamy gray plaques of keratinized
conjunctiva overlying an area of dryness -pathognomonic

6. Vitamin A deficiency
 Puctate keratopathy which progresses to epithelial defects,
keratinization and stromal edema.
 Corneal epithelial defects progress to partial or full thickness
ulceration
 Keratomalacia is often associated with preceding systemic stressors
like measles or severe protein malnutrition.
 Descematocoele/corneal perforation

7. Vitamin A deficiency
 Xerophthalmic fundus-numerous small yellow dots representing loss
of pigment from the RPE
 Replenishment of vitamin A stores typically results in the reversal of
night blindness and conjunctival and retinal pathology.
 Keratopathy without severe ulceration also responds favorably .

8. Production of retinoic acid
NATURAL PRODUCTION IN THE BODY
 Produced in body by 2 oxidation steps:
 retinol  retinaldehyde
 Retinaldehyde  retinoic acid
 Retinol ingested in food  absorbed by intestinal cells bound to
serum retinol-binding protiens transported to target epithelial cells.
 Most organs have the capacity for retinoic acid biosynthesis
including corneal epithelial cells

9. Production of retinoic acid
SYNTHETIC PRODUCTION
 2 methods known in literature for synthetic production of retinoic
acid both for therapeutic and research purposes
 Both lead to formation of all-trans retinoic acid
 It is inherently unstable because it undergoes photoisomerization.
 Retinol/ retinyl palmitate, another derivative of vitamin A is more
stable and is the precursor or storage form of vitamin A

10. Mechanism of retinoic acid action
Two main mechanisms
1. Nuclear receptor mediated pathway
2. Non nuclear receptor medicated pathway
 Studies have shown nuclear receptor pathway to be the primary
pathway.
 Retinoic acid binds to nuclear receptors that act as ligand
activated transcriptional factors, resulting in either
 Transcriptional activation or
 Repression of retinoid controlled genes

11. Mechanism of retinoic acid action
Nuclear receptor mediated mechanism
 Regulates the transcriptional level of target genes
 Retinoic acid binds to nuclear receptors conformational changes gene
transcription
 Increased gene transcription  upregulation of protiens  transactivation
 Decreased gene transcription  downregulation of protiens  transrepression
 TRANSACTIVATION is mediated by 2 families of nuclear receptors RAR* and RXR
 Promotion of ocular surface hydration,
 Epithelial healing
 Ocular differentiation and development

12. Mechanism of retinoic acid action
 TRANSREPRESSION results in a reduction of keratinization, protection
of the cornea from dissolution, and suppression of oncogenic
proliferation and neoplasia
 Transrepression leads to
 Reduction of keratin production
 Inhibition of collagenases production
 Possible down regulation of MMP 13 production(which plasys a role in
pathogenesis of OSSN)
 Down regulation of AP1 transcriptional activity inhibiting oncogenic
proliferation and cellular proliferation.

13. Mechanism of retinoic acid action
Non nuclear receptor mediated mechanism
 Binding to extra nuclear retinol receptors,
 Retinoylation,
 Activation of or interaction with other signaling molecules
 Mediation of effects via metabolites
 To summarize..*
 Corneal epithelial cell repair
 Maintenance of ocular surface hydration - MUC 16
 Apoptosis, cellular differentiation and repression of oncogenic
proliferation
 Reduction of keratininzation of ocular surface epithelium

14. Role in wound healing
1. ROLE IN FULL THICKNESS CORNEAL WOUNDS
 Application of retinoic acid increases the tensile strength
 Retinol palmitate was compared in two doses 0.1 % and 0.5%
which showed a significant increase in tensile strength with 0.1 %
concentration
 0.5% not only had any effect on wound healing or tensile
strength, it also showed an inhibitory effect in high doses.
 An ideal concentration of 10 x 10 -6 m equivalent to 33%
increased keratocyte numbers

15. Role in wound healing
2. ROLE IN NON PENETRATING CORNEAL WOUNDS
 Increased rate of corneal epithelial wound healing with the use
of all-trans-retinoic acid -variable results have been reported with
retinol palmatate
 1954- Agarwal et al - intramuscular vitamin A accelerated the
healing time for both superficial and deep non penetrating
corneal wounds while also decreasing the density of scar
formation.
 Use of IM vitamin A in 3 groups of human patients;
1. Non sloughing,
2. Sloughing
3. Hypopyon associated corneal ulcers.

16. Role in wound healing
3. ROLE IN CORNEAL EPITHELIAL DEFECTS
• Topical application of retinoic acid benefits epithelial healing
time
• Vetrugno et al - role of oral vitamin A & E in re-epithelialization
time and corneal haze formation at 1 year post PRK - significantly
improved re- epitheliazation rates and reduction in formation of
corneal haze which was more pronounced in high myopic
corrections
• Novel methods of delivery of all-trans-retinoic acid -egg shaped
Nano particles
• Showed earlier wound healing but higher concentration was
both cytostatic and cytotoxic.

17. Role in cell differentiation-cornea
 Retinoic acid 0.001- 0.1% reverses corneal keratinization and improves
histological appearance of the cornea.
 Improvement of surface keratinization in the untreated contralateral eye.
 Wright & Herbort et al showed an improvement in persistent epithelial defects
with use of 0.1% retinoic acid at bedtime
 Corneal surface becomes flatter, more wet able and regular
 Retinoic acid concentrations greater than 10 -6 M equivalent to 3.3% induce
 Abnormal differentiation,
 Poor polarity and
 Increase mucin staining

18. Role in cell differentiation-conjunctiva
 Retinoic acid helps improve conjunctival keratinization
 Controlling conjunctival fibroblast activity which as implications for cicatrizing
conjunctival disease
 Tseng - pts whose conjunctival impression cytology improved with the use of
retinoic acid:
 KCS
 SJS
 Pseudo-pemphigoid
 Surgically induced dry eye
 Retinol palmitate - higher concentrations (1500 IU/ml) improve goblet cell
numbers compared with placebo in a dose dependent manner.

19. Role in cell differentiation-limbus
 Retinoic acid is vital for correct limbal differentiation but only in correct
concentration
 It differentiates limbal stem cells into transient amplifying cells that go on to
epithelize the cornea
 Ideal concentration 0.003 – 0.3% required for normal expression of limbal
progenators and markers.
 Where limbal stem cells are irreparably damaged, a process of trans-
differentiation occurs
 In the presence of viable limbal stem cells, retinoic acid acts to encourage
corneal regeneration from this source.
 When all stem cells are destroyed, re-epithelization occurs across the limbus
from conjunctival cells and is once again influenced by retinoic acid

20. Role in cell differentiation-anti
tumour effect
 Positive effect of all-trans-retinoic acid in reversing squamous metaplasia
 Retinoic acid changes keratinocyte membrane glycoconjugates and this may
alter intra-cellular adhesions that control growth.
 Retinoic acid has the potential to contain but not cure neoplastic lesions
 Synergistic combination with other agents such as interferon alpha2b is done
for management of ocular surface dysplasias.

21. Role in cell differentiation-
mebomian glands
 Main limiting factor to the use of retinoic acid is its dramatic effect on
mebomian gland.
 Even systemic use of retinoic acid decreases mebomian gland function
 Atrophy of the acini
 Hyposecretion of oil
 Tear osmolality and
 Evaporation

22. Role in dry eye
 Mebomian gland dysfunction is the most frequent cause of dry eye.
 On impression cytology, reversal of squamous metaplasia, increase
in goblet cell density with use of topical retinoic acid 0.001 to 0.1%
 Retinyl palmatate 0.05% vs cyclosporine A 0.05% for treating the
inflammatory component of dry eye disease
 2011- international workshop on mebomian gland dysfunction-
hyperkeratinization of the orifice and ductal epithelium led to
mebomian gland obstruction.
 Retinoic acid only has a role if ocular surface keratinization is the
predominant mechanism of dry eye and not in mebomian gland
dysfunction.

23. Recent developments
 Various studies have shown that retinoic acid is involved in the
 Photo-receptor differentiation and development,
 Lens development and regeneration
 Barrier function and trans-differentiation of retinal pigment epithelial
cells,
 Prevention of micro ophthalmia
 Establishment of immune tolerance in the eye
 In animal studies, retinoic acid decreased the severity of optic
neuritis and auto-immune uveo-retinitis.
 Inhibited human lens epithelial cell proliferation raising the possibility
of its use for pcos.

24. Drug dosage

25. conclusion
 This review looks at the role of retinoic acid on the ocular surface. It
has been shown to improve full and partial thickness corneal
lacerations as well as corneal epithelial defects. Its positive effect is
only achieved at the correct concentration, however; excess
concentrations of retinoic acid have a deleterious effect. The main
limiting factor of retinoic acid use is its detrimental effect on
meibomian glands, resulting in cell death, atrophy of acini,
hyposecretion of oils, and altered gene expression, eventually
resulting in dry eye symptoms. This effect is reversible on
discontinuation of the drug.