Abstract

A 57-year-old English speaking Caucasian female presented to the UVA Eye Clinic for a comprehensive exam and to re-establish optometric care. The patient reported longstanding decreased vision in her left eye secondary to “complications from her prescription” and previous trauma. Upon chart review from the last eye exam at UVA in 2004, the patient was reported to have degenerative myopia with Fuch’s spot in the left eye and a history of multiple photodynamic therapy sessions. The patient was currently in a monthly disposable contact lens in the right eye only and was wearing progressive lenses over the contact lenses.

The systemic history was remarkable for hypertension. This was managed with oral medication.

On manifest refraction, the right eye was corrected to 20/30 with a prescription of -15.25 -2.50 x 172 and the left eye was hand motion with NI on manifest refraction.

A dilated fundus exam revealed a posterior staphyloma, Fuch’s spot over the macula, peripapillary atrophy with temporal discs, lattice degeneration with laser scarring, white without pressure, a posterior vitreous detachment and significant vascular attenuation in the left eye. There is also an active choroidal neovascular membrane with adjacent fluid in the right eye seen on OCT.

Introduction

Myopia is the most common ocular disorder around the world, with an estimate of 49.8% of the global population being affected by 20501. Although this refractive error can be corrected by simply prescribing a pair of glasses or contact lenses, it is important to remember that this condition can potentially threaten a person’s eyesight. This is through retinal detachments, accelerated onset of nuclear sclerotic and posterior subcapsular cataracts, higher incidence of primary open angle glaucoma and the development of pathological myopia. Although pathological myopia is a specific subset of myopia, it is crucial to diagnose and be familiar with the various clinical findings and management strategies.

Throughout literature and in the clinical setting, pathological myopia has been called several other terms which all ultimately describe the same disorder. These terms include degenerative, malignant, pernicious, progressive high, and myopic retinopathy which all have varying definitions depending on what text is referenced. The American Academy of Ophthalmology defines degenerative myopia as “refractive error of greater than -6.00 D with an axial length of more than 26 mm”2. The Handan Eye Study defines myopic retinopathy as “a spectrum of pathologic abnormalities affecting the posterior pole of the sclera, choroid, and retina”3. Some references include specific numeric thresholds for refractive error and/or axial length in their definition while others do not. The inconsistency across this topic is challenging for the patient, physician, and researcher as all six terms ultimately define the same condition. The purpose of this paper is to propose a single name for the condition and to discuss the clinical implications of the fundus findings in order to provide the best patient care.

Defining Myopia

The etiology behind the root cause of myopia is multifaceted; it is a combination of genetics and our environment. Studies have shown a definite genetic basis for high myopia and a strong genetic basis for low myopia4. When an eyeball is myopic, the entering light rays are brought to focus in front of the macula, rendering a blurry image. Two reasons for this are via the axial length being too long or when the optical power of the cornea and/or crystalline lens is abnormally high in eyes with a normal axial length. This is known as refractive myopia and axial myopia, respectfully.

Due to the wide range of myopic prescriptions, it is important to classify each degree to better understand the risk of further ocular complications. The general stages of myopia include mild, moderate, and high. However, the range of prescriptions under each stage is also not universally agreed upon. A report published by the WHO notes that “there is currently no internationally agreed threshold for myopia or for high myopia”5. This proves another challenge to the clinician, as the inconsistency makes it difficult to classify patients.

Some studies define mild myopia as -0.25D up to -1.25D or -1.50D. Different sources define moderate myopia between -1.50D to -6.00D or between -2.00D to -7.90D. The same holds true with high myopia, as this can begin at -5.00, -6.00D or -8.00D. Additionally, high myopia has been defined when the axial elongation is greater than 26.5 mm. Multiple studies have shown that eyes more than -6.00 had a greater risk of visual loss than smaller amount of myopia, which is why this should be the threshold for defining high myopia6,7.

Pathological Myopia

Pathological myopia occurs when fundus abnormalities develop that are related to the degree of myopia. These fundus findings are vast and include myopic maculopathy, diffuse chorioretinal atrophy, posterior staphyloma, Fuch’s spot, choroidal neovascular membrane, tilted optic discs, lacquer cracks, and foveoschisis. Additional findings of standard myopia that are seen more frequently in pathological myopia include retinal detachments, tears, holes, lattice degeneration and peripapillary atrophy.

There is no standardized, clear cutoff in terms of refractive error or axial length to diagnose pathological myopia. The numerical amount of myopia can vary, as there have been cases of myopic maculopathy in patients with a prescription of less than -6.00D2. Patients’ prescriptions can be over minused or there can be a lack consistency on manifest refractions due to accommodative variability behind the phoropter11. This also creates a dilemma in eyes that have had refractive procedures such as corneal surgery, phakic intraocular lenses, or cataract extractions. After the surgery, the refraction of the eye may be minimized, yet there is still a risk of pathological myopia. Axial length also does not play a direct role in the definition, as posterior staphylomas have occurred in eyes with that are smaller than 26.5 mm8. However, we know that the primary risk factors of developing pathological myopia include a high myopic prescription greater than -6.00 D, axial length > 26.5 mm, and positive family history. A patient will most likely have one of these three factors if they have pathological myopia. If the patient has one of the above fundus findings, they cannot have other underlying pathology contributing to the fundus abnormality.

Clinical Implications in Pathological Myopia

In order to detect any of the above posterior segment findings, it is imperative to dilate myopic patients with a prescription of -6.00D or higher every year, regardless of their age. Another option to supplement the dilated fundus exam is to obtain an OCT macula line scan. A study in 2019 analyzed the difference in the thickness of the outer retinal layers and the choroid and found that pathological myopes have significantly thinner myoid and ellipsoid zone versus in high myopes10. Acquiring a baseline thickness of these layers in high myopes would be useful to reference if later these patients developed any pathological changes.

Key: AL = Axial length, MEZ = Myoid and Ellipsoid Zone

An OCT macula scan also allows the clinician to see if there is any sign of a dome shaped macula, which sometimes cannot be discerned on dilated fundus exam. The presence of dome shaped macula increases the risk of serous retinal detachments, myopic retinoschisis, choroidal neovascularization, and RPE abnormalities due to the anterior protrusion of the macula. Although the pathogenesis is controversial, it is thought to occur as a compensatory response to myopic elongation to distribute tractional forces more peripherally or from scleral resistance11.

A baseline axial length scan would be advantageous to document, as we know that global elongation has a higher risk of damage to the fundus. Structural changes within the optic nerve head, retina, RPE, Bruch’s membrane, choroid, and sclera occur at a higher rate in those with axial lengths greater than 26.5 mm. We also know that the risk of development a retinal detachment is 3 to 7 times greater in patients with myopia greater than 5.00 D, and that the risk is even higher in those with pathological myopia12.

Patients with tilted optic discs should have a Humphrey 24-2 visual field to visualize the extent of the potential bitemporal defects. A baseline 24-2 HVF should also be obtained in pathological myopes because there is a higher risk of POAG development. There are multiple theories behind this discovery including a thinner lamina cribosa, axial elongation that thins the sclera and decreases its resistance to higher IOP, and reduced blood flow within the retinal arteries, making the neuroretinal rim more susceptible to damage. Studies have even shown that patients with moderate to high myopia have a 50% greater chance of developing POAG compared to those with low myopia13. It is important to remember to evaluate POAG suspects carefully when analyzing OCT scans, as high myopes often have enlarged optic discs and areas of peripapillary atrophy, which commonly show as “red disease” on OCT.

Conclusion

A uniform definition for pathological myopia is the first step to provide standardized care and to better understand its clinical implications. Multiple definitions and various thresholds for the refractive amounts and axial lengths provide ambiguity across the eye care field. Pathological myopia occurs when fundus abnormalities develop that are related to the degree of myopia. The primary risk factors we need to be cautious of include having a prescription greater than -6.00D, an axial length greater than 26.5 mm, and positive family history of pathological myopia. Baseline analyses that were discussed will help monitor any changes to the eyes over time.

References

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