7.1 Provide a definition of high-power negative lenses from your research, explaining your rationale.
High power negative lenses refer to divergent lenses with a short focal length. The rationale behind this definition is the meaning of each of these words regarding optometry. In describing lenses, optical power is the extent to which they converge or diverge light. It corresponds to the reciprocal of the lens's focal length, and therefore a short length indicates a higher optical power (Olsen 2012). Combining thin lenses gives a total optical power equal to their sum. In this case, negative power refer to diverging lenses in contrast to the converging lenses that indicate positive power. Based on these descriptions, the definition of a high power negative lens can be elaborated.
7.2 List the optical problems that are likely to be met, and then explain each one.
Refractive errors - They occur when light is prevented by the shape of the eye from direct focus on the retina. Examples are myopia, hyperopia, presbyopia, and astigmatism.
Cataracts - Condition in which the eye lens become opaque, usually due to old age, and therefore produce blurred images.
Conjunctivitis - Reddening of eyes, itching, and swelling due to inflammation. Usually cause by an infection, irritant chemical, or an allergic substance.
Corneal abrasions - Corneal scratches usually caused by a mechanical injury.
Diabetic Retinopathy - A complication of Diabetes Mellitus in which blood vessels of the retina are damaged. Usually causes blindness if not treated.
Glaucoma - condition in which the optic nerve is damaged, usually attributed to pressure build-up in the eye chambers. Usually categorized into open angle glaucoma and angle-closure glaucoma.
Nystagmus - vision problem in which the eye makes abnormal uncontrollable movements resulting in reduced depth perception and vision, usually due to neurological issues such as stroke or trauma.
7.3 List the mechanical problems that are likely to be met, and then explain each one
Mechanical problems likely to be experienced include refractive errors of the eye lenses. Some of the causes for these refractive errors include aging lenses, changes in the shape of the cornea, and lengthening or shortening of the eyeball. These errors include:
Myopia - Condition in which objects that are near are viewed clearly while those that are far appear blurred. In this case, instead of light focusing on the retina, it does so in front of it.
Hyperopia - Condition in which objects located far away appear clearly while those that are near appear blurred. This kind of refractive error may not be notable at early stages but when it progresses, all objects, near and far, appear blurry.
Astigmatism - Condition in which light is not evenly focused on the retina sometimes with many focal points. Therefore, images appear stretched out and blurred.
Presbyopia - Inability of the lens to change shape appropriately to focus close images, usually related to old age.
Source: Atchison, Mathur, and Varnas 2013
7.4 List the range of lens types and forms available to overcome these problems, using diagrams where appropriate.
Refractive errors can be corrected using appropriate lenses inform of eye glasses or contact lenses. Both of them can be tinted, treated with a chemical substance so as to darken automatically in adverse light, or coated to reduce ultraviolet rays from damaging the eyes. Contact lenses serve the same purpose as the eye glasses but are preferred for aesthetic purposes. However, according to Atchison (2011), they provide better peripheral vision and visual acuity than the glasses.
Each of the mechanical optical problems require particular customization in designing the appropriate lenses. Myopia is managed by correctional glasses or contact lenses designed to counteract near-sightedness as recommended by an optician. In this case, a concave lens that is negatively powered is placed in front of the eye that is myopic so as to move the image back to the retina to make the distant image clear. It is as shown in the diagram below.
Source: Atchison, Mathur, and Varnas 2013
On the other hand hyperopia is corrected by placing a convex lens that is positively powered in front of the eye that is hyperopic so as to move the image forward to focus on the retina. The image below shows how it works.
Source: Atchison, Mathur, and Varnas 2013
Astigmatism is managed by lenses depending on whether the refraction error is causing myopia or hyperopia as described above. Additionally, an additional cylinder lens power is required in correcting the difference between the two eye meridian principles (Olsen, 2012). The astigmatism axis in contact lenses or eyeglasses is associated with the flatter principal meridian of the eye location using the 180-degree rotary scale shown below.
Source: Olsen 2012
Presbyopia is corrected using multifocal lenses with powers prescribed for near and distant focus. These patients also have an option for mono vision contact lenses in which one eye has a lens for near vision and the other for distant vision. This method leads to automatic vision depending on the image situation.
7.5 Outline any other factors that can provide solutions for the high myope
High myopia refers to a severe form of near-sightedness in which the eyeball grows bigger and may lead to other complications. Although the use of appropriate contact lenses or glasses are considered sufficient in such cases, pathological changes are likely to occur. Examples of potential risks include posterior vitreous detachment, glaucoma, and retinal detachment. Therefore solutions for those with high myopia should consider other factors other than distance focus. For instance, according to Atchison (2011), low vision aids such as magnifying lenses may be used with recommendations from an eye specialist. Since there are no treatments currently for controlling the growth of the eye, management focuses on improving vision and treating complications as they appear (Olsen 2012). It is for this reason that such patients need regular visits to an eye specialist for assessment of the level of care needed. Resulting conditions such as glaucoma are then treated with eye drops.
7.6 Reflect upon your learning and how this will affect how you recommend lenses for high negative powers in future in practice
This topic has provided various insights about common optical problems and how they can be solved. Of particular importance are the refractive errors that are usually corrected by lenses. These lenses are customized to assist in focusing of objects on the retina to produce a clear image. Therefore, the knowledge gained will be of great importance in recommending lenses for patients experiencing problems with focusing. Reflecting upon what I have learned, I will be able to dispense lenses for high negative powers in my practice appropriately. According to Atchison (2011), these lenses are used in the correction of myopia because they diverge light from an object before reaching the retina to prevent focusing in front of the retina. Those with a high power are required in patients suffering from hyper myopia to cause a divergence large enough for a good focus. These teachings will be consistently applied when dealing with hyper myopic patients to improve their vision.
Responsibilities of a Dispensing Optician
Dispensing Opticians are professionals in eye care whose primary responsibilities include assisting customers to select and fit in contact lenses and eye glasses. Their work is based on the prescriptions given by an ophthalmologist or an optometrist. In consideration of the facial features of a person, their occupational habits, they help their clients to choose lenses, frames, and coatings that are relevant to their needs. After this assessment, they give specifications such as the prescription, colour, style, material, and size to the technicians of an ophthalmic laboratory who then inserts lenses into the appropriate frames. After making of the glasses, they are also required to reshape frames according to the shape of the face of a client.
Another responsibility for dispensing opticians include fixing and fitting glasses already owned by the clients. Additionally, they advise customers on how to use the lenses and cautionary measures to prevent damage or infections. Other than their roles regarding lenses, they undertake administrative duties such as keeping financial records, prescriptions, inventories, and advising on sale orders. Those that have more training may also assist clients to fit contact lenses, artificial eyes, or cosmetic shells. Those that deal in contact lenses are mandated to advise customers on insertion, removal, and caring for them.
Source: (Study.com 2017)
Atchison, D. (2011). Third-Order Theory of Spectacle Lenses Applied to Correction of Peripheral Refractive Errors. Optometry and Vision Science, 88(2), pp.E227-E233.
Atchison, D., Mathur, A. and Varnas, S. (2013). Visual Performance with Lenses Correcting Peripheral Refractive Errors. Optometry and Vision Science, 90(11), pp.1304-1311.
Olsen, T. (2012). Intraocular lens power calculation errors in long eyes. Journal of Cataract & Refractive Surgery, 38(4), pp.733-734.
Study.com. (2017). Dispensing Optician: Job Description, Requirements and Outlook. [Online] Available at: http://study.com/articles/Dispensing_Optician_Job_Description_Requirements_and_Outlook.html [Accessed 17 Mar. 2017].
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