New research published in the British Journal of Ophthalmology investigated the use of intravitreal (IVT) injections of hydroxypropylmethylcellulose (HPMC) for the treatment of chronic structural hypotony.
First, let’s get a refresh on hypotony.
What it is: A rare vision-threatening eye condition in which intraocular pressure (IOP) is extremely low (think: < 6.5 mm Hg) for months—see here for possible causes—eventually causing the eye’s internal structure (retina and choroid) to collapse or detach.
- The resulting impact: Potentially permanent vision loss (if left untreated).
Speaking of treatment, how is it typically managed?
Through either medical or surgical methods—varying from relatively straightforward to more complicated—depending on the specific cause and clinical impact of the condition.
And in general, the goals for these methods entail:
- Reversing the causative pathology
- Maintaining the eye’s anatomical integrity
- Restoring any compromised visual function
Give me some examples.
A common method: To fill the eye with silicone oil after vitrectomy in order to maintain its shape and support its internal structure.
- To note: While this can be beneficial, it’s also “not ideal as it can be toxic to eye structures over long periods of time and is difficult to see through.”
Other methods include a bandage contact lens to manage leaking blebs following filtering surgery, or even systemic corticosteroids, systemic nonsteroidal anti-inflammatory drugs, topical steroids, and a local injection of steroids, to name a few.
But on the whole: There’s no true, established standard of care for treating this condition.
So why focus on HPMC?
HPMC is known as a low-cost, biocompatible gel often used in ocular surgeries as a viscoelastic agent (essentially a liquid bandage) to offer protection and to maintain the eye’s shape.
- And most importantly: It has a reputation as being safe for use in increasing the volume (specifically, size and pressure) of eyes with hypotony.
- See here for supporting data on it.
Duly noted. Now to this research.
Investigators from the Moorfields Eye Hospital Hypotony Service—established in 2021 as the world’s first hypotony-dedicated clinic and funded by Moorfields Eye Charity— conducted a prospective interventional case series on eight patients.
Its purpose: To identify and report on the resulting visual and anatomical outcomes following an IVT injection of HPMC among patients diagnosed with chronic structural hypotony.
And what do we know about these patients?
Each of the eight participants (aged 21 to 80; median age of 40) included in the study demonstrated evidence of visual potential, a clear cornea, and a clear visual axis.
They were also required to have the following inclusion criteria:
- A chronic hypotony diagnosis (>3 months or >6 months after the last revision of over-draining filtration surgery)
- An IOP of < 6.5 mm Hg
- At least one structural change in the eye
See here for exclusion criteria and click here for the clinical phenotyping all participants underwent.
Next up: the study method.
The setup: Patients received multiple IVT HPMC injections (varying from 70 µL–1400 µL), administered every 2 to 4 weeks, until either:
- Pre-morbid axial length (AL) was achieved
- An IOP of 10-15 mm Hg was sustained for 4 weeks without signs of hypotony
- AL of the contralateral eye was reached
The duration: Patients were followed up to 12 months following their first IVT injection.
Exactly how many injections did each patient receive?
That number varied … however, the study authors noted the median number of injections per eye as 9, with a range of 4 to 13, as well as a median volume of 214 µL (range: 94–650 µL).
As for the median total volume injected at 12 months—that would be 2,145 µL (range: 350–4,380 µL).
And what was measured throughout the 12-month period?
Investigators tracked:
- Best-corrected visual acuity (BCVA) improvement
- IOP changes
- Central macular thickness (CMT) changes
- AL variation
… and the findings?
Starting broadly: 87.5% of patients (7 out of 8) experienced vision improvement 12 months after starting treatment.
Breaking this down, we’ll take a look at BCVA improvements.
- The initial median BCVA was 1.14 LogMAR (range: 0.3-1.7), while the median final BCVA at 12 months was 0.4 LogMAR (range: 0.1-1.6).
- See here for a visual of these changes.
Next: IOP changes.
The median initial IOP was 3.5 mm Hg (range: 1-5 mm Hg), while the median IOP at 12 months after treatment initiation was 9 mm Hg (range: 3-23 mm Hg).
As such, the median increase in IOP was 5.5 mm Hg over the 12-month period.
- Check out this graph of the changes.
And those remaining two measurements?
CMT variation underwent a decrease over the 12-month treatment course, as evidenced below:
- Median initial CMT: 379 µm (range: 227–779 µm)
- Median final CMT: 314 µm (range: 277–393 µm).
- See here for a visual of this variation.
Similarly, AL variation also saw a slight decrease throughout the study period.
- Median initial AL: 22.4 mm (range: 18.6 mm-24.9 mm)
- Median final AL: 23.1 mm (range: 21.5 mm–24.8 mm)
- Check out this graph of the changes.
Were there any adverse events reported?
Yes—two observed in four eyes of four patients.
Two of those eyes developed a uveitic flare during treatment, which resulted in a “loss of clarity of the HPMC within the vitreous chambers,” the authors noted.
- Topical and IVT corticosteroids were used to manage the development, with the patients’ vision improving; however, one of the two patients was offered a vitrectomy with an HPMC refill following the study’s conclusion.
As for that second adverse event: Two patients (two eyes) experienced transient vision loss immediately following the 11th and 4th injections—which was resolved after paracentesis.
How about study limitations?
While this investigation was noted by the authors as “the first prospective study of the effect of a protocol-driven hypotony treatment plan,” they also called out its drawbacks.
Most significantly: the small sample size and lack of control group.
- See their explanation and recommendations for future research, including the use of randomized controlled trials to establish more “robust evidence.”
And the final takeaways from these results?
Despite those critical limitations, the study authors concluded: “The findings from this case series suggest that intravitreal HPMC injections may be a valuable addition to the management options for chronic structural ocular hypotony.”