Vitreous: Definition & Components
The vitreous (vitreous humor) is a transparent, gel-like substance that fills the space between the lens and the retina in the posterior segment of the eye. It helps maintain the shape of the eyeball and provides a pathway for light to reach the retina.
Components of Vitreous
- Water (99%) – Provides transparency and maintains shape.
- Collagen fibers (Type II, IX, XI) – Provide structural support.
- Hyaluronic acid – Helps in hydration and gel consistency.
- Proteins & Other Molecules – Maintain biochemical stability.
- Cells (Hyalocytes & Fibroblasts) – Involved in collagen and hyaluronic acid synthesis.
- Metabolites – Oxygen, glucose, and electrolytes.
Important Points:
- Vitreous is avascular and gets nutrients from the surrounding structures.
It is firmly attached at three main sites:
- Vitreous base (strongest attachment, near ora serrata).
- Optic disc margin.
- Macular region.
With aging, it undergoes liquefaction (syneresis), leading to posterior vitreous detachment (PVD), a risk factor for retinal tears.
Vitreous Hemorrhage (VH)
Vitreous hemorrhage refers to the presence of blood within the vitreous cavity, which can significantly impair vision by blocking light from reaching the retina.
Causes of Vitreous Hemorrhage
- Retinal causes (most common)
- Diabetic retinopathy (proliferative type → neovascularization)
- Retinal vein occlusion
- Retinal tear or detachment
- Age-related macular degeneration (AMD)
- Blunt or penetrating eye injuries
- Ocular surgeries (postoperative bleeding)
- Hypertension
- Blood dyscrasias (e.g., leukemia, sickle cell disease)
- Posterior vitreous detachment (PVD)
- Inflammatory conditions (vasculitis, uveitis)
Clinical Features (Symptoms & Signs)
- Sudden painless vision loss (unilateral, if trauma-related it can be bilateral)
- Floaters (perceived as black dots, cobwebs, or a reddish haze)
- Photopsia (flashes of light if associated with retinal tear)
- Reduced red reflex (appears dull or absent on ophthalmoscopy)
Diagnosis
- Clinical Examination
- Visual Acuity Testing – Determines the extent of vision loss.
- Slit Lamp Examination – Identifies red blood cells in the anterior vitreous (Tyndall effect).
- Dilated Fundus Examination – If the view is clear, evaluates the retina for pathology.
Investigations
- B-scan Ultrasonography (USG)
- Used when the fundus is obscured by hemorrhage.
- Detects retinal detachment, tumors, or vitreoretinal pathology.
- Fluorescein Angiography (FFA)
- Assesses underlying vascular disorders.
- Useful in diabetic retinopathy and vein occlusion.
- Optical Coherence Tomography (OCT)
- Evaluates associated macular edema or neovascularization.
Blood Investigations
- CBC, PT, APTT, INR → To rule out blood dyscrasias.
- Blood glucose & HbA1c → If diabetes is suspected.
Treatment & Management
Conservative Management (If Mild & Non-Traumatic):
- Bed rest with head elevation (45°) → Helps settle blood inferiorly, improving vision.
- Avoid anticoagulants (if possible) → Check for underlying coagulopathy.
- Cycloplegic drops (Atropine 1% or Homatropine 2%) → Prevents painful ciliary spasm.
- Close observation → Spontaneous resolution occurs in 2-3 months in mild cases.
Medical Treatment
- Anti-VEGF Injections (Intravitreal Ranibizumab, Bevacizumab) - For proliferative diabetic retinopathy or AMD-related hemorrhage.
- Corticosteroids (Intravitreal or Systemic) - If inflammation is a contributing factor.
- Laser Photocoagulation (Panretinal Photocoagulation, PRP) - Indicated in proliferative diabetic retinopathy and vein occlusion.
- Acetazolamide (Diamox) – Decreases intraocular pressure.
- Timolol, Brimonidine – Topical agents to reduce IOP.
Surgical Treatment (If VH Persists >3 Months):
- Pars Plana Vitrectomy (PPV) – Gold standard - Indicated for non-resolving hemorrhage, tractional retinal detachment, or severe vision loss.
- Retinal Surgery - For associated retinal detachment or tears.
Prognosis & Complications
- Good prognosis if the underlying cause is treated early.
- Complications include:
- Persistent vision loss if hemorrhage doesn’t clear.
- Retinal detachment (especially in trauma cases).
- Neovascular glaucoma (in untreated PDR cases).
Key Points for Exams
- Most common cause of VH: Diabetic retinopathy (proliferative type).
- Investigation of choice if fundus is not visible: B-scan ultrasonography.
- Treatment for non-resolving hemorrhage: Pars plana vitrectomy (PPV).
- Common symptom: Sudden painless vision loss with floaters.
- Role of Anti-VEGF therapy: Useful in neovascular causes (diabetic retinopathy, AMD).