Jennifer C. Chen

Clinical applications and new developments of optical coherence tomography: an evidence‐based review

Optical coherence tomography (OCT) is a new imaging modality that has increasingly become an indispensable tool in clinical practice for the diagnosis and management of ocular diseases involving the macula, optic nerve and anterior segment. The instrument is an advanced imaging technique that provides unprecedented high resolution and cross‐sectional tomographic images of the ocular microstructure in situ, and in real time. Since its introduction about four years ago, a multitude of advantages has made OCT an essential instrument in ophthalmic imaging. The technique has fast image acquisition speed and non‐contact, non‐invasive applicability, allowing a non‐excisional ‘optical biopsy’ to be performed. The purpose of this paper is to provide an evidence‐based review of the increasing role of OCT in the diagnosis and management of ocular disorders, particularly in age‐related macular degeneration, diabetic macular oedema, macular hole, epiretinal membrane and glaucoma. Being one of the first users of OCT in Australia, our clinical experiences will be highlighted and clinical examples of various conditions will be presented to provide an overview of the immense implications of OCT in practice. The latest developments of the OCT revolution, in relation to combining OCT with fundus photography and scanning laser ophthalmoscopy, will also be described. New developments of three‐dimensional visualisation of tissue morphology with future models of ultra‐high speed, ultra‐high resolution OCT may further enhance the early diagnosis, monitoring of disease progression and assessment of treatment efficacy, facilitated by this powerful technology.

Delayed mfERG responses in myopia.

It has been suggested that changes in the multifocal electroretinogram (mfERG) responses in myopes are primarily due to the increased axial length that accompanies myopia development. We investigated the characteristics of mfERG responses between emmetropes and myopes and determined the contribution of axial length to the mfERG data in 30 subjects (10 emmetropes and 20 myopes) using VERIS I. The amplitude and implicit time of the first positive peak (P1) of the first-order kernel were analyzed. We found that P1 implicit time in myopes was significantly longer by 1.3-3.1 ms than that of the emmetropes and this was not explained by the myopes having greater axial lengths than the emmetropes. Axial length contributed to 15% of the implicit time total variance while refractive error accounted for 27%. Delayed mfERG responses observed in myopes were not attributable to the anatomical change that accompanies myopia and may suggest underlying differences in retinal function that result from being myopic.

Posterior placoid chorioretinitis: An unusual ocular manifestation of syphilis

There appears to be a re-emergence of syphilis in recent times despite a steady decline in incidence for the past decade. Diagnosis of syphilis can be clinically challenging and ocular manifestations of syphilis have a myriad of presentations and severity. Ocular syphilis can occur at any stage of the disease and may also be the only presenting sign of syphilis. We report a case of acute unilateral maculopathy, due to posterior placoid chorioretinitis associated with syphilis, in an immunocompetent patient. Ophthalmoscopy revealed a unilateral yellowish placoid lesion at the macula. Syphilis serology was positive confirming active infection. There were no other systemic signs of syphilis. The patient was treated with intravenous benzylpenicillin 1.2 g every four hours for two weeks. The lesion resolved with treatment and the retinal appearance returned to normal. This case highlights the importance of raising clinical suspicion of syphilis in view of unexplained decreased vision and ocular inflammation.

Slow flash multifocal electroretinogram in myopia.

PURPOSE The purpose of this study was to investigate the characteristics of retinal function in myopes using a modified multifocal electroretinogram (mfERG) protocol, the slow flash (sf-mfERG) paradigm, which is thought to primarily reflect responses of ON- and OFF-bipolar cells and emphasize the late response components. METHODS Twenty-eight subjects (10 emmetropes and 18 myopes) underwent mfERG testing using VERIS 5.1.5X. The sf-mfERG stimulus array consisted of 103-scaled hexagons and flickered according to a pseudorandom binary m-sequence (2(13)-1). The stimulation sequence was slowed by inserting three dark frames such that each step in the m-sequence was four frames long (53.3ms). The amplitude and implicit time of the major sf-mfERG waveform features (N1, P1, and N2) of the first-order kernel were analysed. RESULTS Myopes had significantly reduced P1 and N2 amplitudes compared to the emmetropes (F(1,25)=8.818, p=0.007; F(1,25)=6.723, p=0.017). There were no significant differences in N1 amplitude or implicit time between the groups (F(1,25)=1.506, p=0.233; F(1,25)=1.291, p=0.269). CONCLUSIONS Late response components (P1 and N2) of the first-order sf-mfERG responses were preferentially affected in myopia, suggesting possible reduced ON- and OFF-bipolar cell activity. As bipolar cells form the first synapse of the visual system with the photoreceptors to initiate the ON- and OFF-pathways, future investigations of ON- and OFF-systems in myopia are of interest.

Solar retinopathy and associated optical coherence tomography findings

Solar retinopathy is a rare but well‐recognised clinical entity of macular damage, caused by viewing a solar eclipse or direct sun‐gazing. Visual deterioration from solar retinopathy typically ranges from 6/9 to 6/60 and in most cases the visual loss is reversible. We present a case of solar retinopathy following direct sun‐gazing and illustrate the damage within the retinal structure with optical coherence tomographic (OCT) findings. The visual prognosis of solar retinopathy is usually favourable but prevention remains the mainstay of treatment. The optometrist may play an important role in patient education and reassurance, as well as differentiating solar retinopathy from other likely macular abnormalities.

Changes in implicit time of the multifocal electroretinogram response following contrast adaptation

Purpose: Contrast adaptation, produced by prolonged viewing of high contrast gratings, has been suggested to occur at both retinal and cortical locations within the visual pathway. We sought to investigate the characteristics of retinal contrast adaptation using the multifocal electroretinogram (mfERG). Methods: Twenty subjects, with a mean age of 27.8 ± 5.3 years, underwent mfERG testing using VERIS I. The mfERG was measured after 10 minutes of adaptation to 94% contrast, 5 cyc/deg, sinusoidal, vertical gratings and to an equi-luminance blank control. The mfERG stimulus array consisted of 61-scaled hexagons and flickered according to a pseudorandom binary m-sequence (213−1). Changes in amplitude and implicit time of the first-order kernel were analyzed to determine the effect of contrast adaptation on retinal responses. Results: Adaptation to the vertical grating pattern produced a 2.5 ms increase in implicit time, and the response delay was greatest in the more peripheral parts of the retina (7.6° to 30°). Contrast adaptation did not produce statistically significant changes to the amplitude of the mfERG waveform. Conclusions: Contrast adaptation produced by prolonged viewing of high contrast gratings had a significant effect on retinal responses. It has been suggested that contrast adaptation may play a role in the development of nearwork induced myopia; further work investigating retinal contrast adaptation in myopic individuals may be of interest.

Choroidal osteoma: evidence of progression and decalcification over 20 years.

Choroidal osteoma is a rare, benign, ossifying tumour of the choroid of unknown aetiology. In contrast to other types of intraocular ossification, choroidal osteoma is found typically in young healthy females in the second or third decades of life with no history of systemic or ocular disease. Choroidal osteoma is a deep, pale yellow lesion with distinct geographic borders at the juxtapapillary or macular region, with branching ‘spider’ vessels on the surface of the tumour. These features should help differentiate choroidal osteoma from other types of intraocular tumour and the diagnosis can be confirmed with ultrasonography and computerised tomography. Here we report an initially unilateral case of choroidal osteoma, which decalcified over 20 years but during the same period the fellow eye also developed a choroidal osteoma to become a bilateral case. Despite the benign nature of the tumour, vision may be compromised by gradual atrophy of the overlying retina, serous retinal detachment, accumulation of sub‐retinal fluid and sub‐retinal haemorrhage associated with choroidal neovascularisation. Frequent examinations are recommended for patients with choroidal osteoma, for early detection of a subretinal neovascular membrane and potential treatment with laser photocoagulation.

AC/A ratios in myopic and emmetropic Hong Kong children and the effect of timolol§

Purpose: Caucasian children with myopia have elevated response accommodative vergence to accommodation (AC/A) ratios. The purpose of this study was twofold: to determine if response AC/A ratios vary with refractive error and with myopic progression rate in Hong Kong Chinese children, and to determine the effect of beta‐adrenergic antagonism with topical timolol application on AC/A ratios.

Characteristics of fungal growth in soft contact lenses.

Six fungal species (Fusarium sp, Exophiala jeanselmei, Penicillium spp, Aspergillus niger, Paecilomyces spp, and Alternaria spp) were used to inoculate soft contact lenses. Four types of soft lenses were used: high-water (58%) and low-water (38%) content lenses and lenses that were unworn or worn for 1 day. The fungi displayed a range of macroscopic and microscopic features that allowed differentiation of species. There was no statistically significant effect of lens water content on growth rate and only Penicillium spp showed significantly higher growth for worn versus unworn lenses. A number of the fungi showed secretions, thought to be enzymes, which potentially aid in the process of lens penetration.

The Effect of a β -Adrenoceptor Antagonist on Accommodative Adaptation in Hong Kong Children

Purpose: Increased susceptibility to nearwork-induced accommodative adaptation has been suggested as a risk factor for myopia development. We investigated whether accommodative adaptation may explain in part the high prevalence of myopia in Hong Kong children and examined the effect of β -antagonism with topical timolol maleate on accommodative adaptation.Methods: Thirty children (10 emmetropes and 20 myopes) aged between 8 and 12 years were recruited. Tonic accommodation was measured before and after 5 min of video game–playing using an open-field Shin-Nippon autorefractor. Measurements were repeated 30 min after timolol instillation.Results: Children with progressing myopia demonstrated accommodative adaptation following the near task, whereas stable myopes showed counter-adaptive, hyperopic accommodative changes. Timolol increased the magnitude of accommodative adaptation in the stable myopes but had little effect on responses of the progressing myopes or emmetropes.Conclusions: Neuropharmacological modulation of the accommodative system may have a possible etiological role in the progression of myopia.