Topic

#Refraction & Optics

4 articles
  1. Articles 30 Aug 2021 5 min read

    Anomalies of Accommodation

    Ocular accommodation is an integral visual function that optimizes the visual perception through the focusing ability of the crystalline lens. This closed-loop system constantly interacts with the oculomotor system for finer focusing and alignment of the eyes under naturalistic binocular viewing conditions. This write-up is intended to provide an overview of the commonest anomalies of accommodation encountered by an eyecare practitioner through case-based learning. For detailed reading, the readers are requested to refer to Scheiman & Wick.1 The table below provides an overview of the commonest clinical signs, and symptoms seen in different anomalies of accommodation. 1, 2 ANOMALIES OF ACCOMMODATION DIAGNOSTIC CRITERIA ETIOLOGY PRIMARY SIGNS SYMPTOMS Accommodative insufficiency (Not due to sclerosis of the crystalline lens) Accommodation amplitudes (AA) lesser than expected for the patient’s age Usually idiopathic, can result from certain systemic medications Decreased AA for age (2D l

    Dr. Jameel Rizwana Hussaindeen, M.Phil Opt, Ph.D.,FCOVD-I, FAAO
  2. Articles 27 Jul 2021 13 min read

    Astigmatism - The clinical pearls in Refractive care

    Preface: Astigmatism is a common type of refractive error that we come across in vision clinics on a regular basis. It causes the deterioration of retinal image quality and leads to specific vision-related symptoms. Prevalence of this condition is reported to vary with age, gender, and ethnicity. The clinical diagnosis and management of astigmatism necessitate an understanding of its nature and characteristics. Hence, this particular write-up is prepared as a consolidation of integrated information related to ‘astigmatism’ by focusing on its definition, classic types, relevant clinical evaluation components, and appropriate management options. What is astigmatism? Astigmatism is a type of refractive error/ametropia that occurs when parallel rays of light entering the ocular media (non-accommodative state) are not focused well on the retina. In an optical system with astigmatic error, light rays propagate in two different planes and the incident light rays fail to converge at a single f

    Najiya Sundus K. Meethal · Dr. Krishna Kumar Ramani
  3. Articles 1 Apr 2021 12 min read

    Low Vision Assessment

    WHO (ICD-10) defines low vision as “A person who has impairment of visual functioning even after treatment and/ or standard refractive correction, and has a visual acuity of less than 6/18 to light perception, or a visual field less than 10 degrees from the point of fixation, but who uses, or is potentially able to use, vision for the planning and/ or execution of a task for which vision is essential” NPCB (National Program for Control of Blindness) defines low vision as “Visual acuity of less than 6/18 but equal to or better than 6/60 in the better eye with available correction or a visual field loss of less than 10° from the point of fixation”, and, blindness as “Visual acuity less than 6/60 in the better eye or a corresponding visual field loss of less than 10° The goal of low vision assessment is to: Address the visual demands of the patient Identify and evaluate the cause of low vision Assess ocular health Emphasize the need for the patient/ beneficiary Clinical Assessment Maintai

    Dr. Rahul Deshpande
  4. Articles 1 Apr 2021 6 min read

    Refraction Simplified for the Post Graduates

    The optics of the eye normally creates a clear image by refracting rays of light to focus on the retina. Imperfections in this optical system create aberrations and thus blurred images. The goal is to analyze them and devise a means to eliminate them. Lower order aberrations are primarily refractive errors when parallel rays of light after refracting, do not focus on the retina with accommodation at rest. 1. Retinoscopy It is the objective method of detecting refractive errors by a method of neutralization. Point focus formed at a far point of the eye according to its refractive status. For e.g. In a patient with 1 dioptre of myopia, the far point is at 1 meter. For easy mathematical calculations, 1metre is used for retinoscopy. But practically, 66cm is preferred as it is easier to perform retinoscopy at an arm’s length (which is 66cm). The two principal meridia are recognized and power is determined by neutralization. Usually the two meridia are 90 degrees and 180 deg. In cases of obl

    Dr. R Krishna Prasad · Dr. Sayali D Mahajan

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