A guide on how to manage pathological myopia poorly
Invert, always invert - Jacobi
Tell me where I am going to die... so I can make sure I don't go there. - paraphased from Charles Munger
I was kindly asked to provide an article on how to manage patients with pathological myopia. Indeed, myopia is becoming more common, and in Hong Kong where I was born, around 70% of the population is myopic. As a consequence, we are seeing more cases of pathological myopia.
However, despite myopia being an important condition, it is very challenging to write a concise article on how to manage a condition well. After all, excellent clinical management depends on knowledge, experience and also collaborative effort with your patients. On the other hand, it is much easier to know how to do something badly. So, I decide to invert the question and provide you with a series of principles on how to manage pathological myopia poorly! Hopefully, by avoiding these, you will give your patients with pathological myopia a good outcome.
Definition of pathological myopia
Pathological myopic is the presence of structural changes in high myopia, driven by axial elongation and posterior staphyloma.
High myopia is defined as a highly negative refractive error (> −6 to −8 diopters) along with axial elongation (> 26 - 26.5mm). Posterior staphyloma is the main marker and the most common finding of pathological myopia, and occasionally posterior staphyloma can be present in eyes with normal axial lengths. This is defined, by Spaide, as “an outpouching of the wall of the eye that has a radius of curvature that is less than the surrounding curvature of the wall of the eye”. However, in rare cases, pathological myopia has been reported in eyes with only axial elongation without posterior staphyloma.
Rules to follow if you want to manage your pathological myopia patients poorly
Fail to consider myopia as a cause of pathology if the patient is emmetropic or close to it
Imagine a 40 year old patient walking into your consultation room, with thick glasses on, a refractive error of -12D and bilateral macular changes. It is easy in this case to consider pathological myopia as the cause of the maculopathy. However, especially with the advent of cataract surgery and laser refractive surgery, patients with pathological myopia can be emmetropic or low myopic, and often clinicians can fail to consider pathological myopia in these cases.
For example, I sometimes see patients in their 60s with previous cataract surgery having ongoing anti-VEGF injections for neovascular age-related macular degeneration, but upon further questioning and investigations found to have pathological myopia instead, which allow the injections to be stopped. But as these patients are not "highly myopic" due to their previous cataract surgery, the correct diagnosis was not considered.
So, to make the correct diagnosis, you need to recognise the classic signs of a myopic fundus on examination, Optos ultra-wide field imaging and optical coherent tomography (OCT) imaging. These are:
- Optic nerve is often tilted, small with parapapillary atrophy. OCT imaging will often show incorrect segmentation.
- Peripheral retina can appear thin and tesselated. This is best appreciated on Optos ultra-wide field imaging.
- Macula can show posterior bowing on OCT, along with thinning of the choroid and sometimes tractional changes
So, if you see these signs in a patient, you should ask for a history of high myopia and also consider obtaining axial length measurements to confirm the diagnosis.
Fail to consider full spectrum of disease in pathological myopia
Often, when high myopia is mentioned, the initial concern is the risk of retinal tears and detachments. However, vitreoretinal issues are not the only concerns in pathological myopia. Indeed, myopic maculopathy from pathological myopia can be a more important issue, as it causes 12.2% of vision loss in Japan, and is the fourth leading cause of vision loss in Spain (after age-related macular degeneration, glaucoma and diabetic retinopathy).
Myopic maculopathy can cause atrophy (A), traction (T) and neovascularisation (N), and this forms the ATN grading system.
Atrophy
- tessellated fundus only
- diffuse chorioretinal changes
- patchy chorioretinal atrophy
- macular involving atrophy
Traction
- inner or outer foveoschisis
- inner and outer foveoschisis
- foveal detachment
- full-thickness macular hole
- full-thickness macular hole with retinal detachment
Neovascularisation
- macular lacquer cracks
- active macular neovascularisation (2a) or scar / Fuch's spot (2b)
Personally, in clinical practice, I do not always grade every individual patient with myopic explicitly. However, the grading system gives me a model on how the disease can progress in the future and direct my examination and investigation so I do not miss important signs.
If there is no fluid, there is no neovascularisation
This statement is often true when you are treating patients with age-related macular degeneration (AMD), but you cannot rely on the presence of fluid in the diagnosis of neovascularisation in pathological myopia. In myopic neovascularisation, which are type II (subretinal) lesions, they present as an area of thickening in the outer retina without or with minimal subretinal fluid. With high resolution OCT imaging, active lesion will have an area of 'fuzziness' around the border, and the external limiting membrane can be interrupted. However, these subtle signs can be difficult to detect with lower resolution OCT systems.
Why is it the case that fluid is much less prominent in myopic neovascularisation? One theory is that, in most patients with myopic maculopathy, they are relatively young with good retinal pigment epithelium (RPE) function, in contrast to patients with AMD. As a result, their RPE can pump the fluid out of their retina despite the presence of significant exudation as demonstrated in fluorescein angiography.
As a result, myopic neovascularisation can be difficult to diagnose, especially on lower-quality OCT imaging. However, there are two tips to help:
- Myopic patients are very sensitive to distortion caused by neovascularisation, so if your patient with pathological myopia is telling you that there is new distortion, look very carefully on their OCT and do not hesitate to refer to a medical retina specialist for confirmation.
- Always compare your current OCT with previous imaging to look for a change in the outer retina. The Heidelberg Spectralis system is very useful in this regard as it has eye tracking and will line up the B-scans automatically with previous imaging.
The presence of subretinal fluid always means neovascularisation and ongoing anti-VEGF injections are required
In contrast, I have seen patients with pathological myopia being treated with unnecessary anti-VEGF injections due to the presence of subretinal fluid. In these cases, the presence of dome-shaped maculopathy was not recognised, and sometimes the diagnosis of pathological myopic was not even considered due to previous cataract or refractive surgery as discussed before.
Dome-shaped maculopathy is caused by a bulge of in the macular retina, choroid and RPE within the posterior staphyloma. This is often associated with a localised shallow retinal detcahment with subretinal fluid. This is thought to be caused by a relative thickening of sclera underlying the affected area compared to surrounding areas. The subretinal fluid responds poorly to anti-VEGF therapy and photodynamic therapy. Fortunately, the fluid is indolent and visual acuity can remain stable for a long period of time.
The diagnosis can be easy to make if there is a clear dome detectable on OCT. However, the dome can be more ridge like in some cases, and if the ridge is parallel to the OCT b-scan, the diagnosis can be missed unless both horizontal and vertical scans are performed.
Continue to inject anti-VEGF even if there is no signs of neovascular activity
This is another belief that has been borrowed from the treatment of neovascular AMD. In neovascular AMD, ongoing anti-VEGF therapy with a treat-and-extend regime is the preferred approach, as pro re nata (prn) approach can lead to recurrences and further vision loss. Furthermore, cessation of anti-VEGF therapy in neovascular AMD, even after prolonged treatment, can result in a high rate of recurrence (up to 50% in one year from the Fight Retinal Blindness study).
However, patients with myopic neovascularisation behave very differently from those with neovascular AMD, and often only one or two injections are required to achieve quiescence. In the MYRROR study, patients with myopic neovascularisation are randomised to aflibercept or sham treatment with a prn approach. Those patients with myopic maculopathy did very well with aflibercept, requiring a median number of 2 injections within the first 8 weeks and no further injections in the rest of the first year. So, ongoing maintenance injections are not routinely required for patients with myopic maculopathy.
Once again, this finding is likely associated with the underlying health of the RPE, and in most patients with myopic neovascularisation, the surrounding RPE remains relatively healthy and is able to proliferate and grow over the neovascular membrane leadning to quiescence. However, the only patients with myopic neovascularisation I would consider ongoing anti-VEGF injections are those who are elderly and have some signs of AMD, which may indicate suboptimal RPE health.
Failure to consider inflammation as a cause of macular changes in myopic patients
I recall meeting a patient in her late 30s in the uveitis clinic when I was doing my fellowship in Moorfields Eye Hospital. She was around -6D myopic and was thought to have myopic neovascularisation. She would present to the Casualty Department with acute vision loss, receive an intravitreal anti-VEGF injection, and then the macular lesion would improve. However, she was progressively developing more scarring around the macula and her acuity slowly declined. It was only after two years that the correct diagnosis of punctate inner choroidopathy (PIC) was considered, and after starting on a systemic immunosuppressive agent, she finally stabilised. However, much of this vision loss could have been avoided if the correct treatment (anti-VEGF + steroid for the acute event followed by immunosuppression) was started earlier.
In a paper published in 2022, it was found that 11% of patients with patchy atrophy had evidence of previous PIC or multifocal choroiditis (MFC). PIC / MFC lesions are more common in those with macular neovascularisation (81.8% vs 33.9%). Signs that signify PIC / MFC were an elevation of the RPE by homogenous and medium hyperreflectivity material, often associated with disruption of the photoreceptor ellipsoid zone and interdigitation zone, and/or choroidal hypertransmission below the lesions, along with mid-peripheral curvilinear scars and hyperautofluorescence changes.
Currently I have a patient under my care with high myopia and PIC. She has lost her vision in the left eye due to this condition, but her right eye is largely under controlled with systemic immunosuppression. However, despite the lack of inflammatory signs, the myopic maculopathy can continue to progress with further development of lacquer cracks.
Diagnosing far peripheral vascular changes as abnormal in myopic patients
It is important to recognise that pathological myopia is associated with significant peripheral vascular changes. In this patient under my care with high myopia, a fluorescein angiogram was performed to investigate ongoing vision loss despite stable macular appearance. This showed bilateral peripheral vascular non-perfusion.
As Optos imaging becomes more widely available, I am getting more referrals on the peripheral retinal findings in patients with high myopia. Most of these findings are non-pathological.
Indeed, in a paper published in 2014, it was found that peripheral capillary telangiectasia is a common finding in both emmetropic and myopic eye (around 80%). However, peripheral retinal non-perfusion was present in 82.6% of myopic eye vs only 4.8% of emmetropic eye. Furthermore, the perfused area was limited to just beyond the staphyloma border, and none of these eyes developed neovascularisation.
Fail to assess optic nerve adequately in myopic patients
High myopia is a risk factor for glaucoma, and it is associated with longer axial length, larger optic disc size and/or larger parapapillary delta zone. Furthermore, a non-glaucomatous optic neuropathy can develop from parapapillary gamma-zone lengthening of the retinal nerve fibre affecting the papillomacular region. In the case discussed above, it turned out that the cause of loss of vision was, at least partly, due to the presence of myopic optic neuropathy.
However, asssesment of optic neuropathy in pathological myopia is challenging. Structural assessment of the parapapillary retinal nerve fibre layer with OCT is unreliable due to segmentation error. Some authors advocated assessment of the retinal nerve fibre layer and ganglion cell layer thickness on the macular OCT scan in these cases, but if there is a staphyloma or coexisting myopic maculopathy, the disturbance in the anatomy will render this assessment method to be unreliable. Pattern reversal visual evoked potential (p-VEP) is traditionally used for the measurement of optic nerve function, but as this response is driven by macular function, the reliability of this measurement, again, is limited if there is myopic maculopathy. The photopic negative response on the full field electroretinogram (ERG) has been used to assess optic nerve function, but this is a small amplitude response and intervisit variability can limit its usefulness.
Conclusions
Here, I presented eight common pitfalls in managing patients with pathological myopia. I hope that, after reading this article, you will avoid these mistakes and achieve a good outcome for these patients.
About Dr Leo Sheck
Book your appointment now to see Dr Sheck
Dr Sheck is a RANZCO-qualified, internationally trained ophthalmologist and runs a popular and respected practice in Auckland. He combined his initial training in New Zealand with a two-year advanced fellowship in Moorfield Eye Hospital, London. He also holds a Doctorate in Ocular Genetics from the University of Auckland and a Master of Business Administration from the University of Cambridge. He specialises in medical retina diseases (injection therapy), cataract surgery, ocular genetics, uveitis and electrodiagnostics.
