What are the features, diagnosis, and management of thick taut posterior hyaloid in diabetic retinopathy?

Thick Taut Posterior Hyaloid in Diabetic Retinopathy

Vitrectomy with removal of the thickened, taut posterior hyaloid is the definitive treatment for diabetic macular edema that persists despite laser therapy when this specific anatomical finding is present, with approximately 50% of patients achieving 2 or more lines of visual improvement. 1

Clinical Features

The thick taut posterior hyaloid in diabetic retinopathy presents with specific characteristics that distinguish it from other causes of diabetic macular edema:

Anatomical Characteristics

• Thickened posterior hyaloid membrane that remains attached to the macula, creating tangential traction on the retinal surface 2, 3
• The membrane contains cellular infiltration from both glial cells (glial fibrillary acidic protein-positive) and epithelial cells (cytokeratin-positive), which contributes to abnormal vitreomacular adherence 4
• This cellular component distinguishes it from normal posterior hyaloid and may play a pathogenic role in perpetuating macular edema 4

Clinical Presentation

• Diffuse diabetic macular edema that is typically refractory to standard laser photocoagulation 2, 1
• Deep and diffuse pattern of leakage on fluorescein angiography 2
• Visual acuity typically ranges from 20/160 to 20/400 at presentation 3, 1
• The posterior hyaloid appears taut and attached on fundus contact lens examination 3, 1

Important Pitfall

In approximately 30% of cases, what appears to be a thickened posterior hyaloid on preoperative examination may actually be an epiretinal membrane simulating an attached posterior hyaloid 3. This distinction can be difficult to make preoperatively even with careful contact lens examination, but becomes apparent during surgery.

Diagnosis

Clinical Examination

• Stereoscopic slit-lamp biomicroscopy with fundus contact lens after pupillary dilation is essential to identify the taut posterior hyaloid 5
• Look specifically for a visible, thickened membrane creating tangential traction at the macula 2, 3

Optical Coherence Tomography (OCT)

• OCT provides high-resolution imaging of the vitreoretinal interface and can demonstrate the attached posterior hyaloid and associated macular thickening 5
• OCT is valuable for quantifying retinal thickness and monitoring macular edema response to treatment 5
• OCT can help differentiate between true posterior hyaloid traction and epiretinal membrane formation 5

Fluorescein Angiography

• Shows deep and diffuse pattern of leakage in the macula, distinct from focal leakage patterns 2
• Helps identify macular capillary nonperfusion (enlargement of foveal avascular zone), which is a negative prognostic factor for surgical outcomes 5, 1
• FA is particularly useful when vision loss is unexplained or unresponsive to standard therapy 5

B-scan Ultrasonography

• Essential when media opacity (such as vitreous hemorrhage) prevents adequate visualization of the posterior hyaloid and retina 5
• Can assess vitreoretinal traction and rule out retinal detachment 5

Management

Patient Selection for Surgery

Favorable prognostic factors for vitrectomy include 1:

• Preoperative visual acuity better than 20/200
• Absence of significant macular ischemia on fluorescein angiography
• Clearly identifiable taut posterior hyaloid on examination

Poor prognostic indicators include 1:

• Macular ischemia with enlarged foveal avascular zone
• Preoperative visual acuity of 20/200 or worse
• Extensive capillary nonperfusion

Surgical Technique

Vitrectomy with posterior hyaloid removal is performed using the following approach 5:

• 23-, 25-, or 27-gauge vitrectomy system with local monitored anesthesia 5
• Core vitreous removal followed by induction of posterior vitreous detachment from the optic nerve and macula 5
• The attached, thickened posterior hyaloid is lifted and separated from the retina using aspiration, an illuminated pick, or forceps 5, 2
• Off-label use of triamcinolone may help visualize remaining vitreous and facilitate complete posterior hyaloid removal 5
• Peripheral vitreous is shaved to the equator to minimize risk of iatrogenic retinal breaks 5

Timing of Surgery

• Surgery should be considered for persistent diffuse diabetic macular edema unresponsive to laser therapy when a taut posterior hyaloid is identified 1
• Early surgical intervention may be associated with better visual outcomes in appropriately selected patients 3, 6
• For vitreous hemorrhage, the Diabetic Retinopathy Vitrectomy Study demonstrated improved outcomes when vitrectomy is performed within 1 to 6 months of onset 5

Adjunctive Considerations

Pre-operative anti-VEGF treatment may be beneficial 5:

• Reduces duration of surgery
• Decreases number of intraoperative retinal breaks
• Reduces intraoperative bleeding

Cataract management 5:

• Risk of cataract progression following vitrectomy in phakic eyes is high
• Cataract surgery may be performed before, during, or after vitrectomy depending on clinical circumstances

Expected Outcomes

Visual improvement 1:

• Mean improvement from 20/160 preoperatively to 20/80 postoperatively
• 49% of eyes achieve 2 or more lines of visual improvement
• 82% show complete resolution of macular edema within mean of 4.5 months
• 95% demonstrate improvement in clinically significant macular edema

Complications to monitor 2, 3:

• Vitreous hemorrhage
• Rhegmatogenous retinal detachment
• Cataract formation (most common in phakic eyes)
• Mild epiretinal membrane formation
• Intraocular pressure fluctuations, especially in glaucoma patients 5

Follow-up Protocol

• Serial OCT imaging to monitor macular edema resolution 5
• Visual acuity assessment at each visit 5
• Gonioscopy if intraocular pressure is elevated to rule out neovascular glaucoma 5
• Mean follow-up should extend at least 6 months postoperatively, with typical monitoring for 23 months 1

Alternative Management

When vitrectomy is not feasible or appropriate, intravitreal anti-VEGF therapy remains the primary treatment for center-involved diabetic macular edema with vision loss 5. However, the presence of a thick taut posterior hyaloid creating mechanical traction suggests that anti-VEGF alone may be insufficient, as the mechanical component requires surgical release 2, 1.