A recent study published in Diagnostics investigated the variation of retina parameters among patients with primary open-angle glaucoma (POAG) against patients undergoing cardiac surgery.
Give me some background first.
Open-angle glaucoma (OAG) is a multifactorial progressive optic neuropathy with the following characteristics:
- Retinal ganglion cell (RGC) death
- Distinctive morphological changes to the optic nerve head (ONH)
- Thinning of the retinal nerve fiber layer (RNFL)
Additionally, OAG can progress to irreversible vision loss and is cited as the leading cause of irreversible blindness worldwide.
Go on …
Per investigators, recent studies have suggested impairment of ocular blood flow in OAG pathology; however, not much is known regarding the impact of an impaired cardiovascular supply on the structural and vascular parameters of the retina.
Now, talk about the study.
Researchers conducted a prospective, cohort study (NCT04943458) that examined patients who had been diagnosed with OAG and patients undergoing cardiac surgery (CS) with a cardiopulmonary bypass.
They randomly selected one eye from each of the 82 participants (82 eyes total) to be analyzed.
Note: All patients underwent ophthalmological assessment by swept-source color Doppler imaging (CDI) and optical coherence tomography (OCT) in the randomly selected eye.
Who was included in the study?
The study included 82 participants (aged 18 to 99) broken into three groups (see below). Each group was required to meet specified criteria:
- Control patients (n = 30)
- Healthy with no OAG
- No acute or uncompensated chronic disease from anamnesis
- OAG patients c (n = 33)
- Confirmed OAG diagnosis
- Defined as characteristic optic nerve disc (OND) changes and visual field loss consistent with glaucoma using Humphrey (24-2) SITA-FAST)
- Intraocular pressure (IOP) controlled with treatment
- CS patients (n = 19)
- Undergoing planned cardiac surgery with a cardiopulmonary bypass
How was the study conducted?
The complete ophthalmic examination included the following:
- Best-corrected visual acuity (BCVA)
- Slit lamp examination
- Goldmann applanation tonometry (GAT)
CDI was used to determine retrobulbar blood flow parameters of peak systolic velocity (PSV) and end-diastolic velocity (EDV) in the following arteries:
- Ophthalmic artery (OA)
- Central retinal artery (CRA)
- Short posterior ciliary arteries (SPCA)
Porcelot’s formula was used to calculate the resistance index (RI) in the above-mentioned arteries.
Swept-source OCT (SS-OCT) was used to assess:
- ONH structural parameters
- Macular structure parameters
- Vascular parameters
Findings?
The study found no significant difference in retrobulbar blood flow parameters between the OAG and control patients.
On the other hand, several significant differences were found between the CS group compared to the OAG, and the control groups including:
- Mean PSV and EDV were significantly lower and mean RI was significantly higher in the OA and SPCA of CS patients (p = 0.000–0.013)
- CRA EDV was significantly lower and RI was significantly higher in CS patients (p < 0.001)
- RI
Any negative associations?
Negative associations were also found between linear CDR in the ONH and SPCA EDV of CS patients, which the researchers noted as suggesting impaired blood flow in the SPCA could contribute to ONH structural changes.
Also of interest: They noted that ONH structural changes are typical in OAG patients and can occur before visual field damage is detected.
What about in the CS group?
Participants were found to have a reduced ONH vascular disease (VD) similar to OAG patients (compared to the control group).
They also noted that the topographic location of the structural damage at the level of ONH and macula differed, suggesting structural damage at the macula at the macula level is associated with impaired retrobulbar circulation.
Any other differences?
The relationship between structural and hemodynamic parameters was different between the CS and OAG groups; the study authors stated that this could mean reductions in VD cause different impacts, which could be due to poor blood flow regulation in the OAG group.
Limitations?
For starters, the study used a small sample size of CS patients who were older than both the healthy and OAG participants.
Statistical analysis was not adjusted to control for age, which may have influenced the final results.
Also, the CS patients were under several hypertensive therapies, and the impact of antihypertensive therapy on BP and ocular blood flow biomarkers was not explored.
And lastly?
Participants comprised only people of Eastern European origin—meaning the data collected during the study can not be generalized for people of African or Asian descent.
Thus, more research with a larger, diverse sample size is needed.
Take home.
The researchers concluded that their data suggests significant systemic cardiovascular disease could increase the risk of OAG. Further, clinicians should be aware of risk factors unrelated to IOP when managing glaucoma, as these factors may affect the progression of the disease.