Neuroprotective Drugs in Glaucoma

What is Neuroprotection?

• Excitotoxicity (excess glutamate via NMDA receptor overactivation)
• Oxidative stress and mitochondrial dysfunction
• Neurotrophin deprivation (blockage of BDNF/CNTF transport at the lamina cribrosa)
• Vascular dysregulation and ischemia
• Neuroinflammation

Drugs and Agents Under Investigation

1. Brimonidine (Alpha-2 Adrenergic Agonist)

• Status: Most widely recognized neuroprotective candidate with IOP-lowering use already established
• Mechanism: Beyond IOP reduction, brimonidine activates alpha-2 adrenergic receptors in RGCs, upregulating BDNF and other neurotrophic factors; it also reduces glutamate-mediated excitotoxicity and inhibits apoptosis
• Evidence: Preclinical animal studies showed clear RGC survival benefits. Clinical proof remains limited, but brimonidine is already used in normal-tension glaucoma partly for its potential neuroprotective effect
• Kanski's Clinical Ophthalmology notes: "Brimonidine may have a neuroprotective effect in addition to an IOP-lowering effect" in the context of normal-tension glaucoma treatment

2. Memantine (NMDA Receptor Antagonist)

• Status: Failed in clinical trials
• Mechanism: Non-competitive blocker of NMDA receptors; targets glutamate excitotoxicity, which causes RGC apoptosis following pressure-induced axonal damage
• Evidence: Despite strong preclinical rationale and success in Alzheimer's disease, two large RCTs showed no significant benefit over placebo in preventing visual field progression in glaucoma
• Kanski's states: "Memantine is used to retard neuronal death in some CNS disorders, but has not been shown to be beneficial in glaucoma"

3. Nicotinamide (Vitamin B3 / Niacinamide)

• Status: Most promising current candidate - active Phase III clinical trials ongoing
• Mechanism: Precursor of NAD+ (nicotinamide adenine dinucleotide), a coenzyme critical for mitochondrial energy metabolism. Reduces metabolic vulnerability of RGCs and protects against oxidative stress and energy failure
• Evidence:
  • A Phase II RCT (2022, De Moraes et al., JAMA Ophthalmology) in 32 OAG patients found significant improvements in visual field test locations with 3 g niacinamide + 3 g calcium pyruvate (median 15 vs. 7, p=0.005)
  • A Phase III RCT (NCT05405868) is evaluating nicotinamide's effect on VF progression over 27 months, with results expected by 2026
  • The Glaucoma Nicotinamide Trial (TGNT, NCT05275738) is studying 660 OAG patients, also completing ~2026
  • A 2026 crossover RCT (PMID: 41167798) examined effects in normal-tension glaucoma

4. Citicoline (CDP-Choline)

• Status: Available as nutritional supplement; positive supportive evidence
• Mechanism: Naturally occurring compound involved in cell membrane phosphatidylcholine synthesis; reduces glutamate excitotoxicity, lowers oxidative stress in RGCs, supports mitochondrial function, and improves dopaminergic/cholinergic activity
• Evidence: A 2023 systematic review (PMID: 37768938) found citicoline supplementation beneficial in glaucoma patients with well-controlled IOP - improvements in pattern electroretinogram (PERG) and visual field parameters. Recent work (2025) combines citicoline + Coenzyme Q10 for synergistic effects
• Combination studies: Di Simone et al. (2024) and Matamoros et al. (2025) showed citicoline + CoQ10 combined treatment had stronger neuroprotective and antioxidant effects than either alone

5. Coenzyme Q10 (CoQ10)

• Mechanism: Antioxidant that targets mitochondrial electron transport chain; reduces reactive oxygen species in RGCs
• Evidence: Topical CoQ10 + Vitamin E studied in pseudoexfoliative glaucoma; adjunctive CoQ10 + Vit.E preserved visual fields and slowed ganglion cell loss in POAG (Dogan et al., 2025)
• Delivery: Being developed as topical eye drops to overcome bioavailability limitations

6. Ginkgo Biloba Extract (GBE)

• Mechanism: Antioxidant, vasodilatory, and anti-platelet properties; improves ocular blood flow and provides free radical scavenging
• Evidence: Kanski's states "Ginkgo biloba (40 mg three times daily) may confer some benefit in selected cases." Clinical trials remain inconclusive; results are inconsistent across studies
• Dose mentioned: 40 mg TID

7. Neurotrophic Factors

• BDNF (Brain-Derived Neurotrophic Factor): RGCs depend on BDNF for survival. Elevated IOP blocks retrograde BDNF transport, leading to RGC starvation. Exogenous BDNF supplementation (intravitreal injection, gene therapy) is under research
• CNTF (Ciliary Neurotrophic Factor): A Phase I clinical trial of a CNTF intraocular implant (2023) in 11 POAG patients over 18 months showed visual acuity and contrast sensitivity declined more in fellow (control) eyes than implanted eyes. Visual field mean deviation improved in study eyes (+1.2 dB vs. -3.9 dB). Well-tolerated with no serious adverse events

8. Calcium Channel Blockers

• Systemic (e.g., nifedipine, nimodipine): Advocated by some for vasospasm-related normal-tension glaucoma; improve optic nerve perfusion
• Betaxolol: A selective beta-1 blocker used in glaucoma that also has calcium channel blocking properties; may confer some neuroprotection relative to non-selective beta-blockers - this is why it is the beta-blocker of choice in normal-tension glaucoma when nocturnal blood pressure dips are a concern

9. Resveratrol

• Mechanism: Polyphenol with antioxidant, anti-inflammatory, and sirtuin-activating properties; activates SIRT1, which regulates RGC survival pathways
• Evidence: A 2025 systematic review (PMID: 40717982) found promising preclinical evidence; clinical data in glaucoma remains limited

10. Emerging / Novel Agents

Why Clinical Translation Has Been Difficult

1. Slow disease progression - glaucoma progresses over years/decades, making it hard to detect therapeutic benefit in standard trial durations
2. Poor biomarker sensitivity - visual field testing has high variability; structural endpoints (OCT RNFL) may be more sensitive but still limited
3. Heterogeneous disease - different subtypes (POAG, NTG, PACG) may respond differently
4. Patient selection - most trials enrolled mixed populations rather than enriched high-risk groups

Summary Table

Key Point

• Kanski's Clinical Ophthalmology, 10th ed. - Kanski's Clinical Ophthalmology, pp. 952, 966
• Kaplan & Sadock's Comprehensive Textbook of Psychiatry - Kaplan & Sadock's Comprehensive Textbook of Psychiatry, p. 1143
• PMC Review: Advances in Neuroprotection in Glaucoma (2024)
• Review of Ophthalmology: Neuroprotective Therapies Update (Feb 2025)
• Citicoline in glaucoma - systematic review [PMID: 37768938]
• Nicotinamide Phase III trial design [PMID: 41461224]
• Nicotinamide in normal-tension glaucoma RCT [PMID: 41167798]

👁️ Corneal Preservation & Eye Banking - Made Easy & Memorable

🧠 THE BIG PICTURE FIRST

• Can be donated without blood group matching
• Can be stored outside the body for days (unlike hearts or livers)
• Has >90% long-term success after transplant

PART 1: EYE BANKING - THE WHOLE PROCESS

🔑 Memory Anchor: "SPET"

Selection → Procurement → Evaluation → Transplantation

1. DONOR SELECTION

• Age: Up to 70-80 years
• Death to enucleation: within 6 hours (ideally)
• Cornea is recoverable even when other organs are not (due to age, trauma, or systemic disease)

Memory tip: "You can donate if your cornea was healthy and your blood was clean."

2. PROCUREMENT

• Enucleation (whole eye removal) or in-situ corneoscleral disc excision performed in the operating room or morgue
• Done within 6 hours of death (up to 12 hours if refrigerated)
• Sterile technique is mandatory
• Eyes stored at 4°C during transport

3. EVALUATION AT THE EYE BANK

• Clarity of the cornea
• Endothelial cell density (ECD) - the most critical parameter
  • Normal: ~2500 cells/mm²
  • Minimum acceptable for transplant: ≥ 2000 cells/mm²
  • DMEK requires higher quality: ≥ 2200-2500 cells/mm²

4. TRANSPLANTATION

• Used within 4-14 days depending on preservation method
• The eye bank prepares and cuts the tissue (pre-cut tissue for DSAEK/DMEK)

PART 2: CORNEAL PRESERVATION - THE CORE TOPIC

🔑 Master Framework: ACTIVE vs. NON-ACTIVE

ACTIVE METHODS

Method 1: Hypothermic Storage (4°C) 🧊

• The most widely used method in the US and India
• Stored at 4°C in special preservation media
• Slows metabolism, reducing energy needs

Memory trick for M-K medium: "McCarey-Kaufman = Moderate Keeping time (4 days)"

• Contains: TC-199 tissue culture medium + chondroitin sulfate + dextran + gentamicin + streptomycin
• The dextran pulls water out of the stroma (anti-edema effect)
• Stores cornea at 4°C for up to 14 days

Method 2: Organ Culture (34-37°C) 🌡️

• Standard in Europe (especially UK, France, Germany)
• Cornea stored in tissue culture medium at body temperature
• Keeps endothelial cells metabolically active
• Allows longer storage: up to 35 days
• Better endothelial cell evaluation possible
• Tissue is "re-swollen" just before surgery with dextran-containing solution

Hypothermic = slow metabolism (put it to sleep) | Organ culture = keep it alive and working

NON-ACTIVE METHODS

Method 3: Glycerol Preservation (Dehydration)

• Cornea dehydrated in glycerol 85%
• Stored at room temperature for months to years
• No viable cells - used for tectonic/structural grafts (DALK, patch grafts)
• Cheap, long shelf life, available in resource-limited settings

Method 4: Freeze-Drying (Lyophilization) ❄️🌬️

• Cornea frozen then water removed under vacuum
• Very long shelf life (shelf-stable)
• Used for tectonic purposes (no visual restoration)

🔑 QUICK COMPARISON TABLE

PART 3: CORNEAL TRANSPLANTATION TYPES (Eye Bank's Output)

🧅 Think of the cornea in layers (front to back):

EPITHELIUM  ← surface
BOWMAN'S
STROMA      ← 90% of thickness (most bulk)
DESCEMET'S  ← thin membrane
ENDOTHELIUM ← monolayer of ~2500 cells; cannot regenerate

Transplant Types:

Memory trick: "DALK fixes the front, DMEK fixes the back."

PART 4: CORNEAL GRAFT REJECTION

Keratic precipitates on graft, Epithelial rejection line, Descent's rejection line (Khodadoust line), Stromal edema/vascularization

• Most common cause: endothelial rejection
• Most important risk factor: corneal vascularization at time of transplant
• Treatment: intensive topical steroids (hourly prednisolone 1%)
• Non-vascularized cornea has no circulating immune cells - hence immunological privilege

PART 5: RECENT ADVANCES 🚀

1. Nicotinamide Adenine Dinucleotide (NAD+) / Antioxidant Additives

• Adding antioxidants to Optisol-GS to reduce oxidative stress during cold storage
• Extends usable shelf life and protects endothelial cells better

2. Machine Perfusion / Active Preservation 🔬

• Analogous to kidney perfusion machines
• Cornea is "actively perfused" with oxygenated media, allowing:
  • Longer preservation (beyond 14 days)
  • Real-time monitoring of corneal metabolism
  • Dynamic assessment of graft quality before transplant
• Still largely experimental but promising

3. Corneal Cell Therapy (Injectable Endothelial Cells)

• The biggest game-changer: Instead of transplanting tissue, inject cultured corneal endothelial cells directly into the anterior chamber
• The patient lies face-down for 3 hours to allow cells to settle on Descemet's membrane
• Aurion Biotech (Japan/US) - already approved in Japan (2024); Phase II trial completed in US, Phase III expected 2025-2026
• One donor could theoretically treat 100+ patients (vs. one donor = one transplant currently)

4. Stem Cell-Derived Corneas

• Limbal stem cells expanded in GMP labs and transplanted as sheets
• Used for limbal stem cell deficiency (LSCD) (e.g., chemical burns, Stevens-Johnson)
• Autologous (from the patient's own healthy eye) = no rejection risk

5. SMILE Lenticule Banking

• Small-incision lenticule extraction (SMILE) refractive surgery produces stromal lenticules
• These lenticules can be banked and later used for additive keratoplasty (hyperopia, corneal thinning) - [Bievel-Radulescu et al., 2024, PMID: 39182212]

6. AI-Assisted Endothelial Cell Counting

• Automated AI software for specular microscopy analysis
• More accurate and consistent endothelial cell density counts
• University Hospitals/CWRU working on FDA-validated AI tool (2025)

7. Expanded Donor Pool

• Diabetic donors previously excluded for DMEK are now found to be safe (UH research, 2025) - widening the donor pool significantly
• Death-to-preservation times being extended with new protocols

8. Cryopreservation Research

• Long-term storage of corneal tissue with cryoprotectants
• Could enable global stockpiling and supply chain reliability

9. Decellularized / Biosynthetic Corneas

• Acellular corneal stroma scaffolds (from pig or synthetic materials) for countries with severe donor shortages
• Already used in some European centers for DALK

🎯 ONE-PAGE MEMORY MAP

EYE BANK
    │
    ├── DONOR (up to 80 yrs, within 6 hrs, no HIV/CJD/malignancy)
    │
    ├── EVALUATION
    │       ├── Serology
    │       ├── Specular microscopy (ECD ≥ 2000/mm²)
    │       └── Slit lamp
    │
    ├── PRESERVATION
    │       ├── ACTIVE (cells alive)
    │       │     ├── Hypothermic 4°C - Optisol-GS - 14 days [US]
    │       │     └── Organ culture 34°C - up to 35 days [Europe]
    │       └── NON-ACTIVE (structure only)
    │             ├── Glycerol - months
    │             └── Freeze-dry - years
    │
    └── TRANSPLANT
            ├── PK = full thickness
            ├── DALK = front (stroma)
            ├── DSAEK = back (endo + DM + thin stroma)
            └── DMEK = back only (endo + DM) ← most common now

📌 Key High-Yield Facts to Remember

1. First corneal transplant: 1905 (Eduard Zirm) - first successful one in history
2. Eye bank established in US: 1944 (New York Eye Bank)
3. No HLA/blood group matching needed - immunological privilege
4. Moist chamber: 24-48 hrs | M-K medium: 4 days | Optisol-GS: 14 days | Organ culture: 35 days
5. Minimum ECD for transplant: 2000 cells/mm²
6. Most common indication for keratoplasty: Fuchs endothelial dystrophy (US); keratoconus (globally)
7. Most common rejection type: Endothelial rejection (Khodadoust line)
8. Neuroprotective agents of proven benefit are not yet available for glaucoma-associated RGC loss (per Kanski's) - same principle applies to cornea: cell loss is irreversible, hence preservation is everything

• Kanski's Clinical Ophthalmology, 10th ed. - Kanski's Clinical Ophthalmology, pp. 5208-5285
• Henry's Clinical Diagnosis by Laboratory Methods - Henry's Clinical Diagnosis, p. 2533
• [Wang et al., Advances in corneal preservation, Exp Eye Res 2025, PMID: 40882813]
• [Chaurasia et al., Eye banks in India, Indian J Ophthalmol 2024, PMID: 38454864]
• EBAA 2024 Statistical Report
• EyeWorld: Corneal cell therapy 2024