Chromovitrectomy

Definition and Concept

1. Posterior hyaloid face (vitreous cortex)
2. Epiretinal membranes (ERM)
3. Internal limiting membrane (ILM)

Why Chromovitrectomy Matters

Vital Dyes Used in Chromovitrectomy

1. Indocyanine Green (ICG)

• First dye used in chromovitrectomy (Kadonosono et al., 2000)
• Selectively stains the ILM (bright green color)
• ICG binds strongly to collagen type IV in the ILM
• Concerns: Significant retinal toxicity - causes retinal pigment epithelium (RPE) damage, increased apoptosis of ganglion cells, visual field defects. Toxicity related to osmolarity, light exposure, concentration, and prolonged contact time
• Most surgeons have now moved away from ICG due to its toxicity profile

2. Brilliant Blue G (BBG) - the current preferred ILM dye

• Approved for clinical use in many countries (marketed as Membrane Blue-Dual and ILM Blue)
• Selectively stains the ILM with high affinity (blue color)
• Significantly lower toxicity profile than ICG
• Reduces apoptosis compared to ICG
• Preferred dye for ILM peeling in macular hole surgery, macular pucker, and vitreomacular traction syndrome
• Recent safety concern (2025 systematic review, PMID 39566564): Phototoxicity has been reported with BBG and trypan blue; characteristic finding is macular pigmentary change with hypo- and hyper-autofluorescence, often sparing the fovea. Risk factors include prolonged surgery and repeat staining.

3. Trypan Blue (TB)

• FDA-approved for ERM removal
• Primarily stains epiretinal membranes (blue color); stains ILM less selectively than BBG
• Also stains the anterior lens capsule (used in cataract surgery as well)
• Lower ILM affinity compared to BBG - can be used for ERM visualization but may stain both ERM and ILM
• Toxicity: Generally considered safe at standard concentrations; phototoxicity risk at higher concentrations (see PMID 39566564)

4. Triamcinolone Acetonide (TA)

• A corticosteroid, not a traditional "dye" but functions as a vitreous stain
• Crystalline particles deposit on the vitreous cortex/posterior hyaloid, making it visible as white flakes
• FDA-approved (preservative-free formulation) for intraocular use
• Most useful for: visualizing the posterior hyaloid, confirming posterior vitreous detachment (PVD) induction, and checking for residual vitreous on the retinal surface
• No significant retinal toxicity at standard doses; IOP elevation is a known complication

5. Infracyanine Green (IFCG)

• An analogue of ICG dissolved in 5% glucose rather than water (adjusts osmolarity)
• Better osmotic compatibility with vitreous; less toxic than original ICG
• Still has some phototoxicity concerns

6. Sodium Fluorescein

• Used less commonly; stains the vitreous and posterior hyaloid
• Requires blue-light illumination (fluorescence)
• Concerns about toxicity limit widespread use

7. Patent Blue (PB)

• Stains ERM and ILM
• Less selective than BBG for ILM; used in some European centers
• Relatively low toxicity profile

8. Newer/Experimental Agents

• Lutein and anthocyanin from açaí fruit: natural dyes explored as potentially biocompatible alternatives
• Dye-stained perfluorocarbon liquids (PFCL): A recent application - adding dye to PFCL to enhance visualization of these intraoperative tools during complex retinal surgery

Summary of Dye-Tissue Selectivity

Clinical Indications

1. Macular hole surgery - ILM peeling (BBG preferred)
2. Epiretinal membrane peeling - ERM identification (trypan blue or BBG)
3. Diabetic tractional retinal detachment - vitreous base shaving, ERM/ILM dissection
4. Vitreomacular traction syndrome - posterior hyaloid and ILM identification
5. Pediatric vitrectomy - in very young eyes where PVD induction is difficult; TA for vitreous visualization
6. Proliferative vitreoretinopathy (PVR) - complex ERM/ILM removal
7. Giant retinal tears and complex retinal detachment - with PFCL staining

Injection Technique - Key Points

• Slow injection of dye into the vitreous cavity
• Keep injection away from the retinal surface (inject mid-vitreous or just above surface)
• Protect the macular hole when injecting - avoid direct contact with exposed retinal pigment epithelium
• Allow brief contact time, then wash out with balanced salt solution (BSS)
• Use the lowest effective concentration
• Avoid repeat staining (increases phototoxicity risk)
• Use air-assisted technique: fill the eye with air first, then apply dye in an air-fluid interface for more targeted staining (reduces spread, increases concentration at the target)

Complications and Toxicity

The "Ideal" Chromovitrectomy Dye

• High selectivity for the target tissue (ILM, ERM, or vitreous)
• Intense visible color for easy identification
• No retinal toxicity (cellular, mitochondrial, or phototoxic)
• Rapid washout from the eye
• No systemic toxicity following intraocular injection
• Stable shelf life, easy to prepare and use

Evidence Base (Key References)

• Bergamo VC et al. "Role of Vital Dyes in Chromovitrectomy." Asia Pac J Ophthalmol. 2020. [PMID 33252365]
• Farah ME et al. "The Use of Vital Dyes during Vitreoretinal Surgery - Chromovitrectomy." Dev Ophthalmol. 2016. [PMID 26502062]
• Bracha P, Ciulla TA, Baumal CR. "Vital Dyes in Vitreomacular Surgery." Ophthalmic Surg Lasers Imaging Retina. 2018. [PMID 30395665]
• Hernandez F et al. "Chromovitrectomy: an update." J Ophthalmic Vis Res. 2014. [PMID 25279128] (free PMC text)
• Neffendorf JE, Jackson TL. "Presumed phototoxicity from macular vital staining with BBG and Trypan Blue." Surv Ophthalmol. 2025. [PMID 39566564] (most recent systematic review - phototoxicity signal)

Wide-Angle Viewing Systems in Vitrectomy

Concept and Rationale

Optical Principle

1. An indirect condensing lens positioned beneath the operating microscope (replacing or augmenting the microscope's standard optic)
2. An incorporated series of prisms to reinvert the image (since an indirect lens creates an inverted, laterally reversed image, like indirect ophthalmoscopy)
3. The field of view can extend almost to the ora serrata

• Kanski's Clinical Ophthalmology, p. 708

Classification: Contact vs. Non-Contact

Contact Wide-Angle Viewing Systems

• The lens is directly applied to the cornea (with coupling fluid - viscoelastic or BSS)
• Examples: ACCES (Advanced Contact Curved Element System), Volk HM-Retina, AVI (Advanced Vitreous Instrument) contact lenses
• The corneal surface aberration and reflection are cancelled because the lens directly applanates the cornea
• Results in better image resolution and contrast of the fundus
• Disadvantage: the eye position must remain fixed; rotating the eye disrupts contact and degrades the image
• An assistant may be needed to hold the lens in place (reducing bimanual freedom)

Non-Contact Wide-Angle Viewing Systems

• The lens is mounted on the microscope arm or head and floats above the cornea without touching it
• Most widely used systems include BIOM (Binocular Indirect Ophthalmo Microscope) and ROLS (Retinal Observation Lens System)
• Corneal surface must be kept moist with viscoelastic to prevent dehydration; condensation on the front lens can also impair visibility
• Advantages:
  • Surgeon-independent (no assistant needed to hold the lens)
  • Eye can be freely rotated to examine peripheral retina
  • More flexible surgical maneuvers are possible
  • Compatible with true bimanual surgery using chandelier illumination
• Disadvantage: slightly lower image resolution compared to contact systems

Key Comparison

Field of View

Role of Chandelier Illumination with Wide-Angle Systems

• Chandelier probes are small-gauge (25G or 27G), trocar-based, self-retaining light sources inserted through a separate sclerotomy
• They provide diffuse wide-angle illumination of the vitreous cavity without the surgeon holding a light pipe
• This frees both hands for true bimanual surgery - simultaneously manipulating two instruments (e.g., forceps + scissors, pick + cutter)
• Particularly useful in:
  • Complex tractional retinal detachment (bimanual membrane delamination)
  • Giant retinal tear manipulation
  • Chandelier-assisted scleral buckling (see below)
  • Pediatric vitrectomy
• Dual chandelier probes eliminate shadowing artifacts from a single light source

Chandelier-Assisted Scleral Buckling

• Advantages: Panoramic view without head positioning, comfortable for the surgeon, can detect breaks more reliably
• Outcomes: Anatomic success rates and visual outcomes are comparable between contact and non-contact WAVS for CASB (PMID 38454850, multicenter 2024 study: 85% vs 77% reattachment, p=0.34)
• Both systems are valid choices; surgeon preference guides selection

Clinical Indications Where Wide-Angle Viewing is Particularly Valuable

1. Rhegmatogenous retinal detachment - peripheral break detection, ensuring complete vitreous base shaving
2. Proliferative diabetic retinopathy - peripheral fibrovascular membrane dissection, panretinal photocoagulation delivery
3. Giant retinal tears - manipulation of large tears requires constant peripheral visualization
4. Pediatric vitrectomy - small eyes with poor dilation; wide-angle essential for vitreous base work
5. Penetrating trauma - peripheral vitreous base dissection, foreign body localization
6. PVR (proliferative vitreoretinopathy) - circumferential membrane dissection
7. Scleral buckling with chandelier - modern minimally invasive buckling

Limitations and Practical Considerations

Clinical Outcomes Evidence

• A large multicenter study (PRO Study, n=2256 eyes, PMID 32409294) comparing contact vs. non-contact WAVS for primary retinal detachment repair found no statistically significant difference in single surgery anatomic success (p=0.72) or final anatomic success (p=0.40). Any apparent VA advantage with contact systems was lost after controlling for confounders (p=0.097).
• Contact vs. non-contact WAVS for chandelier-assisted scleral buckling showed comparable anatomic and visual outcomes (PMID 38454850).
• The choice between systems is therefore largely surgeon preference and familiarity rather than a difference in outcomes.

Summary

• Kanski's Clinical Ophthalmology, 10th ed., p. 708
• Inoue M. "Wide-angle viewing system." Dev Ophthalmol. 2014. [PMID 25196756]
• de Oliveira PR et al. "Vitreoretinal instruments: vitrectomy cutters, endoillumination and wide-angle viewing systems." Int J Retina Vitreous. 2016. [PMID 27980854] (free PMC text)
• Tieger MG et al. "Contact versus non-contact wide-angle viewing systems - PRO Study." Br J Ophthalmol. 2021. [PMID 32409294]
• Kelkar AS et al. "Chandelier-assisted scleral buckling - contact vs. non-contact WAVS." Indian J Ophthalmol. 2024. [PMID 38454850]
• Pan QT et al. "Novel bubble ultra-wide field viewing system." Acta Ophthalmol. 2022. [PMID 34403213]
• Sadeghi E et al. "Recent developments in surgical vision technologies for vitreoretinal surgery." Expert Rev Med Devices. 2023. [PMID 37394991]

Transconjunctival Vitrectomy (Microincision Vitrectomy Surgery - MIVS)

Historical Background

• Conjunctival peritomy (surgical dissection of the conjunctiva)
• Scleral sutures at each port site at the end of surgery
• Postoperative subconjunctival scarring, longer recovery, and greater patient discomfort

• 2002 - Fujii et al. introduced 25-gauge (0.5 mm) transconjunctival sutureless vitrectomy
• 2005 - Eckardt introduced 23-gauge (0.6 mm) transconjunctival vitrectomy
• 2010 - Oshima et al. introduced 27-gauge (0.4 mm) transconjunctival MIVS (PMID 19880185)

Gauge Sizes and Dimensions

Principle of Transconjunctival Access

The Trocar-Cannula System

1. The conjunctiva is displaced laterally away from the scleral entry site (by 1-2 mm using a cotton-tipped applicator or the trocar tip itself)
2. A sharp-tipped trocar is inserted through conjunctiva and sclera simultaneously in a single step
3. The trocar is removed, leaving a self-retaining cannula in place
4. All surgical instruments (cutter, light pipe, forceps, laser) pass through these cannulas
5. At the end of surgery, cannulas are removed; the displaced conjunctival wound does not overlie the scleral wound - this misalignment prevents vitreous wick formation

• Infusion cannula (usually inferotemporal) - maintains IOP and vitreous cavity volume
• Vitreous cutter port (usually superotemporal)
• Light pipe / accessory instrument port (usually superonasal)

Wound Construction - Critical Technical Points

1. Conjunctival displacement - slide conjunctiva away from the planned scleral entry point before trocar insertion. When the cannula is removed at the end, the conjunctival hole and scleral hole are no longer aligned, preventing a vitreous wick from tracking outward (a major pathway for endophthalmitis)
2. Scleral flattening on insertion - pressing flat on the sclera during trocar insertion creates a longer wound cord length, which improves self-sealing
3. Angled (oblique/beveled) incision - inserting the trocar at an angle (at least 30 degrees initially, then directing posteriorly) creates a tunneled, oblique wound that seals better under IOP than a perpendicular incision; angled incisions have been proven to provide superior wound stability

Instrumentation Components

1. Vitreous Cutter

• Inner guillotine blade oscillating at high speed
• Speed range: 1,500 cpm (older systems) up to 5,000-7,500 cpm in ultra-high-speed cutters (some newer systems reach 10,000-16,000 cpm)
• Higher cut rates = smaller vitreous fragments = less traction on the vitreoretinal interface during aspiration
• 27G cutters historically had lower duty cycles and flow rates (~62% infusion, ~80% aspiration of 25G) but newer designs have substantially closed this gap

2. Infusion Cannula

• Self-retaining in small-gauge systems
• Placed 3.5 mm behind limbus in pseudophakic/aphakic eyes, 4 mm in phakic eyes
• Maintains IOP and volume via balanced salt solution (BSS) or air/gas

3. Illumination (Light Pipe)

• Fibreoptic probe inserted through a port
• Initially MIVS had reduced illumination (halogen bulbs were too dim at small gauges)
• Modern systems use xenon and mercury vapour sources - matching or exceeding 20G illumination levels
• UV/blue light filtration reduces retinal phototoxicity
• Chandelier sources (self-retaining) free both hands for bimanual work

4. Accessory Instruments

• Micro-forceps, scissors, picks, flute needle (for fluid-air exchange), endodiathermy, endolaser probes - all in small-gauge format
• Smaller-calibre cutters can act as multifunctional instruments, reducing instrument exchanges

Advantages of MIVS Over 20G Vitrectomy

Disadvantages and Complications Unique to MIVS

1. Hypotony

• Self-sealing wounds may leak postoperatively, especially if wound construction is suboptimal
• Meta-analysis (PMID 35272553, 22 RCTs, n=1,678 eyes): small-gauge PPV was associated with a significantly greater incidence of hypotony (RR = 3.79; 95% CI 2.02-7.10) and choroidal detachment (RR = 5.65) compared to 20G
• Most cases are transient and resolve without intervention
• If persistent: suturing the wound at surgery end (which negates the "sutureless" benefit)

2. Wound Suturing Rates

• Not all small-gauge wounds seal reliably - some require a suture intraoperatively
• 23G required more frequent port suturing than 25G (RR = 0.46; PMID 35272553)
• 27G achieves the highest sutureless rate: 96.5% sutureless vs. 91.1% for 25G (PMID 38237087, RCT n=463)

3. Endophthalmitis Risk

• A theoretical concern with small sutureless ports - early reports suggested higher rates
• Subsequent larger studies have shown no significantly increased endophthalmitis risk vs. 20G
• Key protective mechanism: conjunctival displacement creating wound misalignment
• Kanski's: "Early concerns about an increased risk of postoperative endophthalmitis do not seem to have been borne out"

4. Instrument Flexibility and Flow Rates

• Very small gauges (27G) have reduced flow rates and aspiration compared to 25G
• Can prolong surgical time in complex cases (vitreous haemorrhage, PDR with thick membranes)
• However, in PDR, 27G beveled-tip was actually more efficient at membrane cutting with fewer instrument exchanges and less intraoperative hemorrhage (PMID 38087284, RCT)

5. Limited Use in Complex Cases (historically)

• Very early MIVS was limited to "simple" cases (macular holes, ERM)
• Modern high-speed cutters and improved instruments have expanded 25G/27G use to complex PDR, retinal detachment, and pediatric cases

Gauge Comparison: 23G vs 25G vs 27G

Current Clinical Evidence

Meta-Analysis of RCTs (PMID 35272553 - Chaban et al., 2022, 22 RCTs, n=1,678 eyes)

• No significant difference in BCVA between 20G and small-gauge PPV
• Small-gauge had higher hypotony (RR 3.79) and choroidal detachment (RR 5.65)
• 23G required more suturing than 25G
• 27G may achieve better final BCVA than 25G (WMD -0.06 logMAR) but requires longer surgery (+4 min)

Large RCT: 25G vs 27G (PMID 38237087 - Benzerroug et al., 2024, n=463 eyes)

• No significant difference in surgery time, BCVA, macular thickness, or complication rates
• 27G achieved a significantly higher sutureless rate (96.5% vs 91.1%, p=0.017)
• 27G is now considered fully equivalent and has advantages in wound sealing

27G in PDR (PMID 38087284 - RCT, 2023)

• 27G beveled-tip was more efficient at membrane cutting in PDR
• Fewer instrument exchanges, less intraoperative hemorrhage
• Equal total operating time; fewer wound sutures needed

Indications (Modern MIVS)

Summary

• Conjunctival displacement + angled tunneled wound = self-sealing without sutures
• 25G and 27G are now the dominant platforms - equivalent outcomes with high sutureless rates
• 27G offers the best wound security (highest sutureless rate) and may be slightly superior for macular surgery visual outcomes
• Residual trade-off: higher hypotony and choroidal detachment risk vs. 20G, but these are usually transient
• Ongoing innovation continues to expand the complexity of cases manageable through the smallest gauges

• Kanski's Clinical Ophthalmology, 10th ed., p. 708
• Oshima Y et al. "27-gauge MIVS system." Ophthalmology. 2010. [PMID 19880185]
• Trichonas G, Kaiser PK. "Wound construction." Dev Ophthalmol. 2014. [PMID 25196754]
• Chaban YV et al. "PPV port sizes: meta-analysis of RCTs." Ophthalmic Surg Lasers. 2022. [PMID 35272553]
• Benzerroug M et al. "25G vs 27G vitrectomy - large RCT." Retina. 2024. [PMID 38237087]
• Liu J et al. "27G beveled vs 25G flat-tip MIVS in PDR - RCT." BMC Ophthalmol. 2023. [PMID 38087284]