Imagewise 65 -Occludable angles, glaucoma, and retinal nerve fiber loss

Dr. Ravi Daberao, Dr. Sarang Lambat, Dr. Prabhat Nangia, Dr. Vinay Nangia
Suraj Eye Institute, Nagpur

Case Description
A female, 59 years of age, presented to us for a regular checkup. Her best corrected visual acuity was 6/6 in the right eye (RE) and 6/6 in the left eye (LE). Her refraction was +0.75DC @100 degrees in the right eye and +1.00 DC @80 degrees with near add +3.00DS in both eyes. Anterior segment examination showed a shallow anterior chamber with Van Herick grade I. Intraocular pressure in both eyes was 16 mmHg on bimatoprost 0.03% eyedrop once a day. Gonioscopy showed occludable angles in both eyes. Her right eye axial length was 23.41 mm and her left eye was 23.65 mm. Central corneal thickness in RE was 513 microns and LE was 507 microns.

Fig.1 Right eye AS-OCT showed aqueous depth (AQD) of 2.53mm (orange line), Anterior chamber depth( ACD) of 3.05mm, Lens thickness ( blue line) of 5.12 mm with lens vault of 0.66mm (yellow arrow).Fig.2 Left eye AS-OCT showed aqueous depth (AQD) of 2.59 mm (orange line), anterior chamber depth( ACD) of 3.10mm, Lens thickness of 5.11 mm (blue line) with lens vault of 0.67mm (yellow arrow). The iris appeared to be very close to the trabecular meshwork but certainly not adherent to it (Fig. 1 and 2, red arrow).

Fig. 3 Colour photograph of the fundus of the right eye showed a cup disc ratio of 0.4 :1 with a normal appearing neuroretinal rim. There was retinal nerve fiber layer loss inferiorly (red arrow).
Fig. 4 Colour photograph of the fundus of the left eye showed a cup disc ratio of 0.6 :1 with inferior rim notching and retinal nerve fiber layer loss (red arrow).

Fig.5 Right eye OCT circumpapillary retinal nerve fiber layer (RNFL) showed significant thinning of temporoinferior RNFL (Fig.5b, yellow arrow) and (Fig.5d, black arrow). There was a decrease in RNFL thickness in the inferotemporal segment of 22 microns (Fig. 5b yellow arrow along green line cursor, and Fig. 5d black arrow along green line cursor). Overall for the temporal-inferior segment, RNFL showed a loss of 4 µm from February 2022 to September 2022.

Fig.6 Left eye OCT circumpapillary retinal nerve fiber layer (RNFL) showed significant thinning of RNFL of the inferotemporal segment (Fig.6b, white arrow) and (Fig.6d, black arrow). The temporal-inferior RNFL segment showed a progression of 4 µm from February 2022 to September 2022.

Fig.7 Right eye posterior pole deviation map showed ganglion cell layer thinning at the region of the raphe (Fig.7 A, red arrow). The macular GCL deviation map showed focal thinning in the temporal area (Fig.7 B, blue arrow) at the first visit. The progression of GCL thinning was noted in the temporal area after 7 months (Fig.7 E, yellow arrow).

Fig.8 Left eye posterior pole heat map showed ganglion cell layer thinning in nasal inferior, nasal and inferotemporal sectors (Fig.8 A, red arrow). The macular GCL deviation map showed thinning in the inferior area, extending temporally and towards the disc (Fig.8 B, blue arrow). The progression of GCL thinning was noted in the inferior area after 7 months (Fig.8 E, yellow arrow). Macular GCL classification showed thinning in the inferior three sectors (Fig.8 D).

Discussion

Our patient presented with the diagnosis of glaucoma. She had occludable angles. In the RE, the axial length was 23.41 mm with an anterior chamber depth of 3.05 mm and her aqueous depth (AQD) was 2.53 mm, the lens thickness was 5.12 mm and the lens vault was 0.66 mm (Fig 1). In the LE, the axial length was 23.65 mm anterior chamber depth was 3.10 mm, and the AQD was 2.59 mm. The lens thickness was 5.11 mm, and the lens vault was 0.67 mm (Fig 2). She had occludable angles, and the angle configuration could be seen in the anterior segment OCT. There was no evidence of primary angle closure or of any synechial closure.

The IOP was 16 mmHg on bimatoprost eye drops. The optic disc of the RE appeared to be healthy clinically, but an inferotemporal RNFL defect had already set in (Fig 3 red arrow, Fig 5 b, c, d). The left eye showed the presence of inferior neuroretinal rim loss along with a broad area of RNFL loss infero- temporally. (Fig 4 red arrow, (Fig. 6 b, and d)).

At 3 months follow-up, the IOP RE was 19 and LE was 17 on bimatoprost eye drops. She was advised to use brimonidine tartrate (0.2%) and timolol maleate (0.50 %) in combination with bimatoprost eye drops.

On follow-up six months later, the IOP was 15 mmHg in both eyes. The RE showed the presence of progressive RNFL loss. While the overall loss in the inferotemporal segment was 4 microns over 6 months, the maximum loss as shown in Fig 5d (black arrow) was 22 microns. There was concomitant ganglion cell loss in the RE (Fig 7 b and e). Even though the sectoral loss was only 4 microns, the manifestation in the ganglion cell deviation map shows a significant increase in the area of GCL loss.

The LE also showed a loss of RNFL in the inferotemporal segment by 4 microns, and the maximum point loss in the segment was 7 microns (Fig 6 d black arrow). The ganglion cell loss shows an increase in area in the deviation map (Fig 8b, 8e).

This patient is interesting because she had an axial length of 23.41 mm in the RE and 23.65mm in the LE. In association, she had a significantly thicker lens at 5.12mm and 5.11 mm in the RE and LE, respectively. While the occludable angle and the lens thickness would suggest a predisposition to angle closure disease, the axial length is a little bigger than what is seen in patients of primary angle closure glaucoma. While the angle was occludable, the angle structures could be seen on extension and on indentation gonioscopy. On the OCT, there were places where the iris appeared to be very close to the trabecular meshwork but certainly not adherent to it ( Fig 1 and 2, red arrows).
These situations are not uncommon, where the angles are occludable, but may not be classically a case of PACG. It is important in such a situation to tread carefully since the decision to do or not to do a laser peripheral iridotomy may need to be made.

Since the patient did not give a history of symptoms of angle closure, we may have the liberty to think that she may have glaucoma but not primary angle closure glaucoma. That would in general change the way we treat such a patient.

She developed progressive RNFL loss over a period of 6 months, even though her IOP in the first visit was 16 mmHg. On her second visit, it was 19 mmHg. She has been advised treatment with brimonidine tartrate (0.2%) and timolol maleate (0.50 %) in addition to her bimatoprost eye drops. While we are used to seeing the changes in the RNFL segments, this only provides an average of loss in that segment. However, if we were to be more precise, we would identify point loss. In the right eye, the segmental difference over two visits six months apart was 4 microns. However, the point loss was 22 microns. (Fig. 5 d black arrow) with a significantly enlarged area of GCL loss on the deviation map. In the LE also, the average segmental loss in the inferotemporal segment was 4 microns (Fig 6d) over 6 months, but the point loss was 7 microns (Fig. 6d black arrow). The GCL loss also showed an obvious increase in the deviation maps (Fig 8b and e).
Our patient has an unusual anterior segment with an axial length of more than 23 mm in both eyes, with a lens thickness of 5.12 mm and 5.11mm in the RE and LE, respectively, without any confirmatory signs of classical primary angle closure glaucoma but in presence of an occludable angles. She also shows the rapid progression of RNFL loss in the inferotemporal segments in both eyes over a relatively short period of 6 months. It may therefore be important to try to identify if there is truly primary angle closure disease as a cause of glaucomatous damage or it is a red herring since the treatment may change accordingly. Also, the rapid progression of glaucomatous damage should be of concern, and treatment may need to be modulated accordingly with lower target pressures and frequent follow-up at shorter intervals.

ReadWise

Abe RY, Gracitelli CP, Medeiros FA. The use of spectral-domain optical coherence tomography to detect glaucoma progression. The Open Ophthalmology Journal. 2015;9:78.
Tatham AJ, Medeiros FA. Detecting structural progression in glaucoma with optical coherence tomography. Ophthalmology. 2017 Dec 1;124(12):S57-65.

Correspondence
Dr Vinay Nangia
MS, FRCS, FRCOphth
Director
Suraj Eye Institute
Email – education@surajeye.org

QuizWise

Q.1 What is the age-related rate of retinal nerve fibre layer thinning?
A) 0.1 micron per year
B) 0.2 microns per year
C) 0.3 microns per year
D) 0.4 microns per year

Q.2 What is the rate of retinal nerve fibre thinning in glaucoma?
A) -1.12 microns per year
B) -2.12 microns per year
C) -3.12 microns per year
D) -4.12 microns per year

Q.3 In which of following the rate of retinal nerve fiber thinning is high?
A) Glaucoma not associated with visual field defect
B) Glaucoma associated with visual field defect
C) Both A and B
D) None of the above

Q.4 Which of the following imaging techniques are useful in monitoring glaucoma progression?
A) Color fundus photograph
B) Optical coherence tomography
C) Visual field
D) All of the above.

QuizWise Answers

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