When examining a patient with visual or visual field disorders, it is important to be aware of small hidden retinal lesions or neuro-ophthalmologic disease that may occur in the absence of obvious abnormal findings on fundus examination using an ophthalmoscope. The accurate reading and interpretation of optical coherence tomography（OCT）findings is important. This article reviews the basics of central foveal structures and retinal microstructures in the normal eyes, and then discusses tips for reading OCT to detect small retinal lesions.

　Most corneal nerves consist of sensory nerves that originate from the first branch of the trigeminal nerve（the ocular nerve）; therefore, trigeminal nerve pathology results in neurotrophic keratopathy. Facial nerve involvement is associated with eyelid closure disorder, inability to blink, lower eyelid ectropion, and lower eyelid drooping, which result in corneal disorders. Additionally, neuropathic ocular pain has recently been attracting much attention in the medical community. In this section, we present a detailed discussion of these issues.

　Both glaucoma and neuro-visual disorders cause chronic visual impairments, making them difficult to diagnose. Additionally, the high prevalence of glaucoma may lead to comorbid neuro-ophthalmologic diseases, particularly in older adults. Herein, I describe a case of a patient who was initially diagnosed with normal-tension glaucoma but later developed ethambutol optic neuropathy. The key elements of diagnosis are the speed of progression of visual field defects, the pattern of visual field loss, and matters regarding MRIs. Thus, I point out a critical but frequently overlooked facet of diagnosis.

　Sagging eye syndrome（SES）was recently reported as a cause of age-onset acquired strabismus. SES is characterized by distance esotropia or small-angle hypotropia, and the characterization of SES has allowed for the diagnosis of previously undiagnosed divergence palsy and small-angle vertical strabismus. In this section, we will review how to distinguish between distance esotropia and divergence palsy, as well as between small-angle vertical strabismus, trochlear nerve palsy, and skew deviation.

　The clinical features and prognosis of 13 patients（8 males and 5 females, mean age: 45.3±19.4 years）with idiopathic orbital inflammation during a 3-year period from 2018 were re viewed. All but one of the patients（92.3%）had unilateral onset, and six（46.1%）were diag nosed with orbital cellulitis at the first visit to the hospital. The average C-reactive protein（CRP）was 0.47±0.74 mg/dl. The extraocular myositis type accounted for 11 cases（84.6%）and inflammation of only a single muscle was most common in seven cases（63.6%）. The most com monly affected muscles were lateral rectus muscle in seven cases, the superior rectus muscle in four cases, and the medial and inferior rectus muscles in three cases each. The relationships be tween the pattern of ocular motility disturbances and the period from onset to first examination were 17.0±14.1 days in four patients with a paralytic pattern, 35.0±41.0 days in two patients with paralytic and contracture patterns, and 93.0±115.0 days in five patients with contracture patterns, with paralytic patterns in the early stages after onset and contractile patterns as the duration increased. All patients showed improvement of clinical symptoms with steroid treatment; however, two patients（15.3%）showed relapse during steroid tapering during the follow-up period. After-effects were observed in four patients（30.8%）, with visual impairment in one and strabismus in three patients. Idiopathic orbital inflammation was characterized by low COP levels with a single affected muscle（especially the lateral rectus muscle）.

　We report two cases of suspected myasthenia gravis（MG）with unilateral ptosis and severe vertical strabismus, in which pathogenic autoantibodies were negative and neuromuscular junc tion disorder was not apparent.

　Case 1: A 60-year-old man visited our hospital complaining of diplopia for the past 6 months. Ptosis and hypertropia of the left eye, and severe limitation of supraduction and mild limitation of abduction of the right eye were observed. A slight waning phenomenon was observed in the or bicularis oculi in repetitive stimulation test; however, oral pyridostigmine bromide was ineffec tive. There was no thymoma, and diplopia was eliminated after 9 months of treatment with oral prednisolone alone.

　Case 2: Four month ago, a 20-year-old man became aware of diplopia, and was diagnosed with Gravesʼ disease and thymoma and underwent thymectomy by a previous physician. However, bilateral exophthalmos, left ptosis, left hypertropia, and severe limitation of infraduction remained. No thickening of the extraocular muscles on MRI, diurnal variation and daily variance were observed; however, pyridostigmine bromide and prednisolone were not effective. Strabismus surgery was performed about six months after the first visit. The intraoperative forced duction test was negative. Diplopia was eliminated although diurnal variation was present for more than 1 year after surgery.

　Both patients had ocular motility disturbances inconsistent with nerve innervation and did not meet the diagnostic criteria of MG; however, the clinical symptoms suggested ocular MG.

　Erdheim-Chester disease（ECD）is classified as histiocytosis and very rarely it may cause orbital lesions. We report the case of a 70-year-old woman with suspected ECD who resisted any treatment that led to blindness in both the eyes. One week prior to the first visit, she noticed a decrease in the visual acuity of the left eye. MRI revealed a mass lesion at the left orbital apex and her condition was diagnosed as left optic neuropathy. After several months, she developed bilateral lagophthalmos from orbititis of both sides. Lacrimal glands were also enlarged bilaterally, and a biopsy of left lacrimal gland was performed. The immunohistochemistry results were consistent with those of ECD, which is classified as histiocytosis. Symmetrical osteocortical sclerosing lesions and gene mutations in the mitogen-activated protein kinase（MAPK）pathway are often found in typical ECD; however, these findings were absent in this case. Although no lesions other than that of the orbit were observed at present, other systemic abnormalities including bone lesions may appear through further observation period, therefore, a careful follow-up is necessary in this case.