OCT helps diagnose macular pathology

Optometry Times Journal, July digital edition 2021, Volume 13, Issue 7

Imaging technology allows for better disease visualization

Optical coherence tomography (OCT) technology has vastly expanded eye care practitioners’ ability to diagnose and manage macular pathology. However, this technology has come with a steep learning curve that can be intimidating for the inexperienced user. This article aims to demystify less common macular pathologies and to provide a framework that can help when encountering something unfamiliar. (Hint: Google is helpful.) If practitioners revert to the basics, such as anatomy of the retina and in which layer the abnormality is located, finding the answer becomes easy.

OCT is an amazing tool, but care must be taken so it doesn’t run the how. It is easy to fall prey to diagnosing “red disease” and “green disease” if allowing OCT to run the show in diagnosis. Red disease involves a scan that looks bad but is not. Examples include optic nerve OCTs when a patient has high myopia or a patient with peripapillary atrophy. Green disease is more dangerous because it occurs when a patient has disease that is missed. In this case, OCT registered the scans as normal, but the doctor did not critically examine the images.

A recent example of this in practice was a woman in her mid-50s presenting for an annual eye exam. The exam proceeded normally with minimal patient complaints, no abnormalities on the anterior segment exam, and intraocular pressure in the mid-teens. The only abnormality appeared in the posterior segment exam where a small Drance hemorrhage was noted on the right optic nerve.

Because of this hemorrhage, a retinal nerve fiber layer (RNFL) OCT was ordered (Figure 1). The OCT image registers all “green,” but focal thinning exists in the RNFL temporal-superior- nasal-inferior-temporal, or TISNT, scan that correlates to the location of the Drance hemorrhage. On visual field testing performed the same day, this patient had a central visual field defect in the right eye (Figure 2) and received a diagnosis of glaucoma. An eye care practitioner quickly glancing at the OCT and seeing all “green” on the image would have easily missed this severe glaucoma.

Most eye care practitioners are familiar with the disease processes they see every day, such as macular degeneration and glaucoma. Following are case examples with less common macular pathologies but are easy to diagnose based on OCT.

Case 1: 30-YEAR-OLD WOMAN

A 30-year-old woman presented for a yearly eye exam to monitor a previously diagnosed macular scar in the right eye. Her vision was good, and she denied metamorphopsias in either eye. Bestcorrected visual acuity was 20/20 in each eye with unremarkable exam findings until the posterior segment. Mild hyperplasia was noted temporal to the macula in the right eye. Previous macular OCT scans were available dating back to 2013 (Figure 3). The scans showed a stable focal dip in the choroid that had been called many things over the years, including a macular scar and a focal posterior staphyloma. The cause of the abnormality was unknown, although the patient remembered an episode of blurry vision in the right eye around the birth of her son in 2011 that resolved spontaneously after a few weeks.

When this patient was seen in 2020, an astute clinician wasn’t satisfied with the diagnosis. Armed with the knowledge of the abnormality’s location and well-reasoned searches, the clinician soon made the diagnosis of focal choroidal excavation (FCE).

FCE lies on the pachychoroid spectrum.1 The pachychoroid spectrum is a constellation of diseases including central serous chorioretinopathy (CSCR), polypoidal choroidal vasculopathy, and pachychoroid pigment epitheliopathy. On OCT, FCE appears exactly as the name suggests, a focal choroidal excavation.

FCE is a relatively new finding, first described in 2006.2 Lee et al studied 41 eyes with FCE and found 10 eyes with central serous chorioretinopathy, 1 with polypoidal choroidal vasculopathy, and 9 with choroidal neovascular membranes (CNVMs).3 However, because the study was conducted at a tertiary medical center, it is likely that the rate of complications is overstated when compared with the general population. For patients with FEC, eye care practitioners should regularly monitor them with OCT.

FCE can present as conforming and nonconforming. In conforming FCE, photoreceptors remain in contact with the retinal pigment epithelium (RPE), showing the contour of the retina and choroid remaining together as illustrated in Figure 3. Nonconforming FCE occurs when the photoreceptors detach from the RPE, creating a hyporeflective space between the RPE and photoreceptors.4

OCT in nonconforming FCE will look like a focal dip in the choroid from which the retina is focally detached. The literature suggests that the majority of FCEs are conforming type. In one case series, only 29% of eyes had a nonconforming FCE. Nonconforming FCE is associated with a higher rate of visual symptoms and associated pathology.3

The etiology of FCE is unknown, although theories posit that FCE may be a congenital malformation or an acquired abnormality. In the acquired theory, researchers hypothesize that FCE may form from choroidal scarring present after inflammatory disease. Chueng et al liken the acquired theory to “an inverse pigment epithelial detachment which may compress choriocapillaris and further exacerbate choroidal ischemia.”1

Although etiology remains unclear, the good news is that FCE is usually a benign finding, and patients can expect to have stable findings long term. In the case of our patient, we believe she may have had CSCR while pregnant, and FCE developed after that. If FCE is congenital, her existing FCE may predispose her to CSCR. Whether the condition is congenital or acquired, she has been stable since 2013, and although I am monitoring her yearly, I expect her to remain stable.

Case 2: 44-YEAR-OLD WOMAN

A 44-year-old woman presented for her first eye exam at the clinic. She reported stable vision in both eyes with no history of ocular disease. Her entering spectacle visual acuity was 20/25+ in the right eye and 20/60+ in the left eye, with pinhole in the left eye at 20/40+. The patient noted that the letters appeared crooked with the left eye.

Preliminary testing was normal, with the exception of Amsler grid testing. The Amsler grid in the right eye showed no scotomas or metamorphopsias, but in the left eye the patient noted that the far right side of the grid was “wiggly.” The patient’s refraction and best corrected visual acuity was +2.50 –4.75 x010, 20/20-1 in the right eye and +3.00 –5.00x160, 20/40+2 in the left eye.

Differential diagnoses are macular in location, and the top differential is dry or wet macular degeneration. While the patient was dilating, fundus photos (Figure 4) and macular OCT (Figure 5) were ordered. The photos showed prominent retinal graying, and macular OCT scans revealed distinctive retinal cavitations and internal limiting membrane (ILM) draping associated with idiopathic juxtafoveal telangiectasia (IJXT) type 2.

IJXT type 2 is an uncommon macular pathology that is distinctive in its retinal appearance. Because the OCT is so distinct, it is often possible to diagnose the condition based on OCT images alone. IJXT type 2 has a prevalence of 0.01% in the general population and has no predilection for men vs women. IJXT type 2 is bilateral, and most patients receive a diagnosis in middle age.5

Although IJXT type 2 is the most common, 2 other types of IJXT can occur. Type 1 is a congenital disease that is primarily unilateral and is relatively rare. IJXT type 1 occurs mainly in males and is an aneurysmal dilation of the blood vessels in the macula.6 A third type of IJXT has an occlusive presentation and is so rare that it is omitted from some classifications of the condition.5

On fundus examination, prominent findings will be the lack of foveal light reflex and a retinal graying or lack of retinal transparency, as with this patient. Patients may present with crystalline deposits and dilated retinal venules at right angles.5 Macular OCT scans will show retinal cavitations that appear as a hyporeflective space in the retina. ILM draping over these areas is a hallmark of IJXT type 2. The patient’s visual acuity is often better than expected based on OCT appearance.

No recommended treatment exists unless patients develop CNVM in later stages of the disease. If CNVM occurs, refer the patient to a retinal specialist to treat with anti–vascular endothelial growth factor (VEGF) injections. Via frequent OCT monitoring, eye care practitioners should be able to catch CNVM in the early stages and make a prompt referral.

Case 3: 55-YEAR-OLD WOMAN

A 55-year-old woman presented for an annual eye exam after moving to the area; she had no specific complaints. Entering visual acuities were 20/20 in the right eye and 20/25 in the left eye. The patient’s habitual glasses were Pl –0.7 5x180 in the right eye and –8.00 sphere in the left eye. The anterior segment and posterior segment exam appeared normal, but because of the high anisometropia and slightly decreased vision in the left eye, a macular OCT scan was ordered (Figure 6).

The scan showed a separation of the inner and outer retinal layers with a posterior staphyloma. Because this was the patient’s first visit and vision was good, I opted to monitor for change in 2 to 3 months.

At the patient’s follow-up visit, an OCT scan showed that the staphyloma and retinal separation was increasing (Figure 7). The patient’s prescription had progressed 0.50 D and best corrected visual acuity had decreased to 20/30-.

These changes indicated progression, and she was referred to a retinal specialist for consideration of surgical treatment.

The patient received a diagnosis of myopic foveoschisis (MF), also called myopic macular schisis, in the left eye. MF is a complication of pathologic myopia. Prior to widespread use of OCT, MF was difficult to diagnose because the retina often looks normal on fundus examination.

As in the case of this patient, a staphyloma is not always apparent on fundoscopy. MF becomes apparent on macular OCT, which shows a splitting of the inner and outer retinal layers that may progress to a macular hole.7 MF is different from a posterior staphyloma on OCT—as with the schisis there is retinal layer splitting, and a staphyloma will not exhibit split layers (Figure 8).

Longitudinal case series suggest that MF has a slow course and can lead to severe central vision loss if untreated. It is not uncommon in eyes with posterior staphyloma and has a prevalence of up to 34.4% in a study of 218 eyes with 8.00 D to 26.00 D of myopia.7 MF should be suspected in myopic patients with slowly progressing decreased vision without apparent cause, especially in the presence of posterior staphyloma. Patients are often asymptomatic and do not notice decreased vision.

Treatment for progressive MF is surgical, most commonly vitrectomy with ILM peel. This can be performed with or without a gas tamponade. The goal of the surgery is to release the abnormal vitreous traction and allow the retina to reattach at the macula. Anatomical success and improved visual acuity are seen in up to 80% of cases after surgery.8 However, success rates are lower if the MF has progressed to a macular hole.

This patient was treated with a vitrectomy and ILM peel and achieved anatomical resolution of the MF and improved visual acuity at 4 months post surgery (Figure 9).

Conclusion

OCT is an excellent tool to have in practice, and it has enabled diagnosis of diseases that were difficult to visualize prior to widespread OCT availability.

Eye care practitioners who feel uncertain about OCT interpretation should consider reviewing interactive tutorials from OCT manufacturers to become familiar with normal retinal appearance on the scans. Use clinical judgment first, of course, but OCT imaging can be a great diagnostic tool and can enhance clinical practice.

References

1. Cheung CMG, Lee WK, Koizumi H, Dansingani K, Lai TYY, Freund KB. Pachychoroid disease. Eye (Lond). 2019;33(1):14-33. doi:10.1038/s41433-018-0158-4

2. Jampol LM, Shankle J, Schroeder R, Tornambe P, Spaide RF, Hee MR. Diagnostic and therapeutic challenges. Retina. 2006;26(9):1072-1076. doi:10.1097/01. iae.0000248819.86737.a5

3. Lee CS, Woo SJ, Kim YK, et al. Clinical and spectraldomain optical coherence tomography findings in patients with focal choroidal excavation. Ophthalmology. 2014;121(5):1029-1035. doi:10.1016/j.ophtha.2013.11.043

4. Chung CY, Li SH, Li KKW. Focal choroidal excavation– morphological features and clinical correlation. Eye (Lond). 2017;31(9):1373-1379. doi:10.1038/eye.2017.71

5. Nowilaty SR, Al-Shamsi HN, Al-Khars W. Idiopathic juxtafoveolar retinal telangiectasis: a current review. Middle East Afr J Ophthalmol. 2010;17(3):224-241. doi:10.4103/0974-9233.65501

6. Charbel Issa P, Gillies MC, Chew EY, et al. Macular telangiectasia type 2. Prog Retin Eye Res. 2013;34:49-77. doi:10.1016/j.preteyeres.2012.11.002

7. Gohil R, Sivaprasad S, Han LT, Mathew R, Kiousis G, Yang Y. Myopic foveoschisis: a clinical review. Eye (Lond). 2015;29(5):593-601. doi:10.1038/eye.2014.311

8. Iida Y, Hangai M, Yoshikawa M, Ooto S, Yoshimura N. Local biometric features and visual prognosis after surgery for treatment of myopic foveoschisis. Retina. 2013;33(6):1179-1187. doi:10.1097/ IAE.0b013e318276e0e8

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