Central Visual Field Changes in Dysthyroid Optic Neuropathy 517

Central visual field changes in dysthyroid optic neuropathy 517

CENTRAL VISUAL FIELD CHANGES IN DYSTHYROID OPTIC NEUROPATHY

Y. INOUE, T. INOUE, T. TSUBOI and K. GOTO

Olympia Eye Hospital, Tokyo, Japan

Abstract

One hundred cases (42 males and 58 females, 23-76 years old) with dysthyroid optic neuropathy were subjected to a visual field examination using Octopus 201 and Goldmann perimeter. One hundred and seventy-eight of 200 eyes were observed to have a visual field defect. Improved visual acuity was seen within a short period of time in 168 of the 178 eyes (94.4%) after combined therapy with local and systemic steroids. The visual field recovered to normal in almost all cases (140/178 eyes, 78.7%). In the remaining 38 eyes, 12 with constriction of the visual field did not recover (11/12). In this series, constriction of the visual field (mostly in the lower hemifield), was the most severe change in patients with dysthyroid optic neuropathy. This evidence suggests that central visual field defects can improve with conservative treatment and attention should be given to changes in the lower hemifield.

Introduction

During therapy for dysthyroid ophthalmopathy (DO), it has been reported that most steroid treatment failures are due to low dosages and poor patient selection1. Pathogenesis of orbitopathy in DO is basically divided into two stages: active and inactive2. Among the various eye changes, the active stage in a patient with optic neuropathy is typically characterized by inflammatory swelling of the extraocular muscle (EOM) at the muscle cone or orbital apex3. In other words, the development of dysthyroid optic neuropathy (DON) occurs during the active stage of orbitopathy. In this study, we evaluated the efficacy of steroid treatment, on the basis of visual field changes, especially central scotoma or central depression in DON.

Subjects

We examined 100 patients with DON; there were 42 males and 58 females, ranging in age from 23 to 76 years, with an average of 51 years. Twenty-two patients were affected unilaterally, and therefore 178 eyes of 100 patients were followed up (Fig. 1).

Address for correspondence: Y. Inoue, MD, Department of Ophthalmology, Olympia Eye Hospital, 2- 18-12 Jingumae, Shibuya-Ku, Tokyo, Japan

Perimetry Update 1998/1999, pp. 517–527 Proceedings of the XIIIth International Perimetric Society Meeting, Gardone Riviera (BS), Italy, September 6–9, 1998 edited by M. Wall and J.M. Wild © 1999 Kugler Publications, The Hague, The Netherlands

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Fig. 1. Distribution of age at onset.

Table 1. Characteristics of dysthyroid optic neuropathy

1. ‘Apex sign’ of enlarged extraocular muscle (EOM) determined by orbital CT or MR 2. Optic disc changes Class a. mild edema or hyperemia Class b. moderate retrobulbar neuritis-like changes Class c. marked papillitis, possible chorioretinal fold 3. Presence of visual loss such as decrease of visual acuity and/or visual field changes (except in some class ‘a’ optic disc changes)

The characteristics of DON are shown in Table 1. We excluded patients with other eye changes that might have accounted for visual impairment (keratopathy, maculopathy, glaucoma, etc.). At the time DON was diagnosed, almost all patients were in the euthyroid stage, whether under medication or not.

Methods of examination

Visual field

The visual field was examined as follows: 1. Goldmann perimetry including five isopters. The types of visual field defects are classified in Table 2, including normal visual fields. Except for central scotoma and

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Table 2. Types of visual field defect

Central scotoma (solid) S Central depression D Large blind spot (Mariotte) M Paracentral scotoma P Constriction with central depression C Normal visual field N

large blind spots, the position of the visual field defect was classified as inferior, superior, temporal or nasal in the case of central depression, paracentral scotoma and constriction. 2. Computerized perimetry was performed with the Octopus 201, Program 31. Total loss and mean loss with the Delta analysis were employed to ascertain whether there was an improvement of visual sensitivity.

Orbital imaging

1. Computerized orbital tomography, axial and coronal sections 2. Magnetic resonance imaging (MRI) (Fig. 2) T1 weighted axial, coronal and sagittal sections T2 weighted coronal section4 3. Morphological changes of the optic disc (Fig. 3) Class a. mild: edema or hyperemia Class b. moderate: retrobulbar neuritis-like changes Class c. marked: papillitis, possible chorioretinal fold 4. Florescein angiography

bilateral unilateral

Fig. 2. Apex sign on MRI with enlarged extraocular muscle (EOM).

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Fig. 3. Distribution of optic disc changes at onset.

Methods of treatment

All patients were treated with bethamethasone. Treatment consisted of intravenous injection of bethamethasone (starting with 8-12 mg) for 14 days and retrobulbar injection of bethamethasone (4 mg) ultimately for ten or 14 days, each eye needing five to seven treatments. If a successful response to the treatment was obtained, defined as an improvement of two or more lines of visual acuity, the second dose administered was the amount of bethamethasone given in the previous administration decreased by a third to a half. After four days, the next dosage was determined in the same way. This treatment lasted for ten to 14 days. The total dosage was basically 100-150 mg of bethamethasone. Some patients

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Table 3. Four-day tapering method

Duration Dose of Method of bethamethasone (mg) administration (1) (2)

4 days 12 8 ↓↓ 4 days 8 6 intravenous injection ↓↓ 4 days 4 4 ↓↓ 2 days 2 2 ↓↓ 4 days 1 1 oral

continued oral administration of the steroid for several days after the study period. When a distinct effect was obtained after four days with the first dosage of 12 mg, the second dosage was the first decreased by one-half (Table 3).

Results

Visual acuity recovered in almost all the patients (168/178 eyes). Even in patients with a starting visual acuity of less than 0.1, there was a high frequency of recovery (Fig. 4). The recovery pattern of visual acuity after treatment is shown in Figure 5. At one week after treatment, good results could already be seen (p<0.0001 Mann-Whitney). After two weeks, visual acuity gradually recovered, even though drug administration had been stopped. Optic disc changes occurred in this series. According to our criteria, there were frequent retrobulbar neuritis-like disc changes (82/178 eyes) (Fig. 6). At the onset of each of the optic disc changes, visual field defects were classified into six types, including normal visual field. Central depression was most frequently observed. Central scotoma and large blind spots were relatively frequent. In eyes with Class a, mild changes in visual field defects were observed, evenly distributed among all types of visual field defect, except in severe changes (constriction and central scotoma). Central depression was frequency observed in Class b eyes. Central scotomata were significant in Class c (Fig. 6). After treatment, the visual fields of almost all eyes returned to normal (140/178 eyes). The remaining 38 eyes had various types of visual field defects. In particular, the visual fields of eyes with constriction did not recover to normal (11/12 eyes). Paracentral scotoma were seen in the five remaining eyes, and in six eyes a slight constriction remained in the lower hemifield. In this series, the most severe changes of the visual field were seen with constriction. Central scotoma (27/47) recovered to normal after treatment, while in the 20 remaining eyes in which there was slight improvement, various types of visual field defects were seen, with the changes being noticed in the lower hemifield (Fig. 7). According to our results, visual fields with central depression, large blind spots and paracentral scotoma significantly recovered to normal after treatment. Improvement of visual sensitivity was also ascertained by computerized perimetry. The changes in total loss on Delta analysis, exhibited during the follow-up period, are shown in Figure 8. There are a number of lines going upwards, indicating significant recovery of

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Fig. 4. Distribution of visual acuity before and after treatment.

Fig. 5. Recovery pattern of visual acuity after treatment.

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Fig. 6. Distribution of visual field defects at the onset of each optic disc change (Classes a, b and c). C: constriction; S: central scotoma; D: central depression; M: large blind spot; P: paracentral scotoma; N: normal.

Fig. 7. Recovery pattern of visual field defects. C: constriction; S: central scotoma; D: central depression; M: large blind spot; P: paracentral scotoma; N: normal.

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Fig. 8. Changes in total loss in the pre- and post-treatment periods.

visual sensitivity. The recovery pattern of visual sensitivity had the following characteristics: total loss had decreased at one week after treatment, and then gradually recovered at a rate of 100dB/week until the third week when it reached a plateau (Fig. 9).

Discussion

In this study, the ‘apex sign’ was observed in almost all eyes. This is defined as DON in which the optic nerve is compressed by the enlarged extraocular muscles at the orbital apex (1978). Even in the cases without the apex sign, three or four enlarged muscles were observed on CT scan or MRI. Apex findings have been reported by several authors to be the cause of optic neuropathy in the case of DO5,6. Since it has been recognized that eye muscle edema could be detected by measuring T2 relaxation times with MRI4, we used T2 weighted examination. The results of our treatment were successful in this study, for which we selected patients with an active stage of orbitopathy.

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time after treatment (weeks)

Fig. 9. Recovery pattern of visual field defects.

In the present study, we looked at the effect of steroid treatment given by two methods: systemic administration and local administration by retrobulbar injection of bethamethasone. We selected doses considered to be sufficient to produce a therapeutic effect. Although we used total doses of bethamethasone ranging from 100-150 mg, the side-effects were minimal due to the short duration of treatment (two weeks). Even though, in some cases, hiccups, insomnia, stomach disorders and slight Cushingoid features, were observed, in general these complaints did not cause any serious problems. There were some patients who had a relapse of DON when medication was tapered off or discontinued. In these cases, we usually switched to irradiation therapy by lineac, and then started on steroid treatment again7. We present representative examples of a Delta analysis in a mild and a severe case. In the mild case, good recovery of central sensitivity of 0-10° was seen, which was considered to correspond to visual acuity. However, in the lower quadrants, remaining mean loss was observed. This recovery pattern of total loss is specific to DON changes, as has been reported earlier (Table 4). In the severe case, a recovery pattern of total loss was observed. Also in this case, the mean loss in the lower hemifield did not decrease; however, the mean loss in eccentricity of 0-10° gradually returned to normal values (Table 5). Finally, with regard to the pathogenesis of DON, it is considered that the enlarged muscles at the orbital apex directly compress the optic nerve. It is also possible that it may be associated with impairment of the venous circulation due to increased orbital pressure8. From these findings, inflammation of the muscles and optic nerves themselves should

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Table 4. A recovery pattern with the Octopus Program 31 (mild case: 69-year-old male)

Exam 1 Exam 2 Exam 3 Exam 4 Exam 5

Date of examination 24/4/97 26/5/97 28/5/97 9/6/79 5/9/97 Program/examination 32/01 32/03 32/04 32/05 32/06 Total loss (whole field) 780 379 166 18) 0 Mean loss (per test location) whole field 10.5 5.1 2.2 0.2 0.0 quadrant upper nasal 10.7 5.2 1.5 0.0 0.0 lower nasal 11.5 5.8 3.7 0.3 0.0 upper temporal 10.7 5.4 1.8 0.0 0.0 lower temporal 9.2 3.9 1.9 0.7 0.0 eccentricity 0-10 8.6 2.8 1.3 0.0 0.0 10-20 8.9 4.2 1.8 0.0 0.0 20-30 11.8 6.1 2.7 0.4 0.0 No. of disturbed points 66 47 25 3 0 Root mean square fluctuation 4.2 0.9 1.6 2.4 1.5

Table 5. A recovery pattern with the Octopus Program 31 (severe case: 52-year-old male)

Exam 3 Exam 4 Exam 5 Exam 6

Date of examination 27/7/95 1/9/95 20/9/95 14/12/95 Program/examination 31/05 31/06 31/08 31/09 Total loss (whole field) 1043 876 189 164 Mean loss (per test location) whole field 15.1 12.7 2.7 2.4 quadrant upper nasal 12.8 10.2 3.6 1.4 lower nasal 20.8 17.5 4.3 5.2 upper temporal 12.4 11.2 3.5 2.5 lower temporal 13.9 12.7 0.0 0.9 eccentricity 0-10 14.1 10.4 0.7 0.6 10-20 15.1 11.6 2.2 2.1 20-30 15.4 14.0 3.6 3.0 No. of disturbed points 66 66 20 22 Root mean square fluctuation 1.3 4.4 2.6 3.6

be recognized as an important factor contributing to the pathogenesis of DON9,10. We be- lieve that, in this study, the anti-inflammatory effect of the steroid played a role in the improvement of DON.

Conclusions

Visual acuity recovered in almost all patients (168/178 eyes) and most visual fields also recovered to normal (140/178 eyes) with this treatment. However, eyes with constriction did not recover normal visual fields (11/12 eyes). In DON, morphological changes of optic disc precede functional deficits of vision.

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References

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