Modification of common low vision devices for uncommon needs.

Creativity in the field of low vision is certainly a necessary requisite when trying to solve a patient's individual needs. Four different categories of low vision devices--hand magnifier, stand magnifier, telescope, and absorptive lens--were modified initially to meet a particular patient's requirement(s). The devices modified were: 1) a +28 aspheric hand magnifier; 2) a magnetized stand magnifier to assist patients in stabilizing a stand magnifier; 3) a focusable telescope held on a gooseneck stand; and 4) a flip-up frame for the Corning CPF series of lenses. These modifications could be of benefit to other patients.     

Prescribing near magnification for low vision patients

Most patients with low vision request help with reading. Despite improvements in the assessment of visual functions, determining the appropriate magnification for reading still often involves a trial and error approach. Recent research has shown that with accurate and systematic assessments of vision, the required magnification can be predicted but this magnification needs to be much higher than has been previously recommended. This paper presents a systematic approach to enable practitioners to determine the power of a near addition or simple magnifier needed to assist patients with mild or moderate low vision who may present seeking help for reading. Guidelines for appropriate referral to low vision services are also provided.     

Stand magnifiers for low vision: description,prescription, assessment

Stand magnifiers are still one of the most commonly prescribed classes of low vision devices. Their performance can be difficult to understand because stand magnifiers usually do not give an image at infinity. This review summarises the methods of describing image enlargement for stand magnifiers, emphasising their relationship to equivalent viewing distance (EVD). This is done in terms of the underlying optical equations, and measurement methods, and methods of prescribing. In the past, methods of determining EVD have been somewhat indirect, requiring accurate measurement of lens power, and image position. The use of digital photography provides an alternative, more direct, simpler method of determining EVD, which can be accomplished in-office. This method is described and it is demonstrated how it gives comparable results to older methods with small, clinically non-meaningful differences, that may be due to differences in image distance reference planes. Describing the performance of stand magnifiers in terms of their dioptric power, or in terms of ‘nominal magnification’ or ‘trade magnification’, is imprecise and misleading. It is better to use indices such as equivalent viewing power and EVD, which take into account the magnifier dioptric power, the image position of the magnifier and the distance a patient is from the magnifier. While EVD is a useful index for prescribing stand magnifiers, manufacturers do not always provide sufficient technical details to determine EVD for their stand magnifiers, and available tables of EVDs are more than a decade old and are likely to need updating. Photographic comparison provides a method for determining EVD, and this method can also be applied to other low vision devices.     

Low vision correction for high myopia.

High myopia is favorable for low vision corrections because the vision has usually been poor since childhood and the person has been able to read at close range, producing magnification. For near vision, in addition to bringing objects close, magnification is produced by high-add bifocals, trifocals, strong near vision spectacles and nonspectacle magnifiers. Hand magnifiers held at a distance from the eye are used with the spectacle correction. This paper describes the Visolett, used without correction or near vision correction, as the preferred non-spectacle magnifier because the reading area is self-illuminated, it doubles the approach magnification, rests on the paper, is simple to use, produces binocular vision, and attracts the least attention. Combination method of magnification consists in the use of the Visolett in addition to a spectacle magnifier, which doubles the magnification.     

手持放大镜对阅读速度的影响

目的探讨手持放大镜对视力正常者和低视力患者阅读速度的影响。设计前瞻性对照研究。研究对象初次使用手持放大镜的低视力患者13例和37例视力正常者。方法分别测试视力正常者不用手持放大镜阅读小五号字及初次使用＋10D、＋20D两种不同度数的手持放大镜、采用10cm、35cm两种不同距离阅读小五号字时的速度;并测量低视力患者首次使用手持放大镜阅读小五号字和不用放大镜阅读相同放大率的大字印刷体的阅读速度。主要指标阅读速度（字数／分钟）。结果视力正常者不用手持放大镜的阅读速度（194．6±45．2字／分）比用＋10D手持放大镜在眼睛到放大镜10cm（159．7±44．7字／分）、35em（162．5±46．7字／分）的阅读速度快,也比用＋20D手持放大镜在眼睛到放大镜10em（150．3±43．3字份）、35cm（150．0±43．4字,分）的阅读速度快,差异有统计学意义（P=0．001、0．002、0．000、0．000）;在相同放大倍率下,眼睛到放大镜的距离分别为10cm和35cm时,阅读速度的差异没有统计学意义（＋10D,P=0．783;＋20D,P=-0．981）。低视力患者首次使用手持放大镜阅读小五号字的速度（54．2±8．2字／分）比不用放大镜阅读相同放大率的大字印刷体的速度（64．0±9．4字／分）要慢,两者相比差别有统计学意义（P=0．000）。结论初次使用手持放大镜阅读者,无论是正常人还是低视力患者阅读速度均慢。因此低视力患者使用放大镜时要有熟练过程。（眼科,2010,19：139—141）     

Nomographs for the Optical Properties of Simple Magnifiers*

ABSTRACT A general solution for equivalent power F_c magnification M_g and linear field of view W for the simple magnifier is presented in the form of two nomographs. The nomographs are useful in demonstrating graphically how a variation in a ‘user’ parameter for a simple magnifier, such as object distance, image vergence, accommodation or spectacle near addition, or eye-to-magnifier separation can change the equivalent power and theoretical field of view of the eye-magnifier system.     

A marble used as a low-vision reading aid: a case report

An unusual low-vision remedy was encountered in which a simple dime-store marble was used in near vision tasks. Although the marble was found satisfactory as a low-vision aid, the patient could be better assisted with a commercially available magnifier of lesser dioptric power. This case serves to demonstrate a patient's ingenuity in independently solving his own low vision problem.     

Reading speed through different equivalent power low vision devices with identical field of view.

Adequate reading speed is one of the criteria low vision patients may use to assist them when they are comparing and selecting equivalent power low vision devices. Inherently, various optical devices of equivalent power will produce different fields of view. We compared the reading speed of 32 trained, normal observers with 4 commonly prescribed types of low vision devices of +12 D equivalent power (spectacles, hand magnifier, stand magnifier, and telemicroscope) which were modified to provide nearly identical fields of view. Our results show that only the reading speed obtained with the telemicroscope was significantly different from those of the other systems (p less than 0.01). Implications are that the field of view provided by a low vision device is the primary parameter limiting reading speed of equivalent power devices.     

Designing half-eye binocular spectacle magnifiers

The process of designing half-eye frames with a smaller than usual eye size and narrower distance between lenses (DBL) in order to produce additional base-in prism effect is described. This method enhances binocular function while the spectacle magnifier is used. The design also provides a lighter, thinner, and cosmetically more acceptable optical aid. Binocular half-eye spectacle magnifiers are useful optical aids, especially for patients with binocular vision, because they are produced in strong powers with strong prism effects incorporated in the lenses. The magnifiers range in power from +6.00 D [symbol: see text] 8 delta base-in to +14.00 D [symbol: see text] 18 delta base-in for vision ranging from 20/60 (6/18) to 20/320 (6/96). Binocular half-eye spectacle magnifiers are recommended for prolonged reading because the strong base-in prism effect relieves the convergence effort, also providing a large field of vision with both hands free.     

Results of treatment in amblyopia associated with unilateral high myopia without strabismus.

Fifty-five patients with amblyopia in unilateral high myopia without strabismus were treated. Thirty-two (58%) had a visual improvement by two lines or more on the Snellen chart and 17 (31%) attained a final visual acuity of 6/12 or better. In patients with pretreatment corrected vision of 6/60 or better in the amblyopic eye treatment consisted of full-time occlusion of the good eye, in some cases supplemented by the after-image method of pleoptic exercises in the amblyopic eye. Overall improvement of vision in this group was 72.7%. Occlusion of the good eye combined with pleoptic exercises in the amblyopic eye had no advantage over simple occlusion of the good eye. In patients with pretreatment corrected vision worse than 6/60 in the amblyopic eye occlusion of the amblyopic eye was done and the after-image method of pleoptic exercises was instituted. Improvement of vision in this group was 36.3%. The study showed that it is worth the trouble to treat this disorder even after the age of 14 years and stresses the utility of pleoptic therapy in older patients with severe amblyopia.     

Technical Note: The Relationship Between Magnification and Field of View for Simple Magnifiers

ABSTRACT The optical performance of a simple magnifier depends in part on the way it is used by the patient. Clinicians often find that aids do not appear to deliver their ‘rated’ magnification, and patients report that aids of stronger dioptral power perform worse than weaker aids. This paper reviews the relationship between magnification and field of view of a simple magnifier using conventional formulae, and suggests a method of instructing a patient in the use of an aid to obtain its maximum performance.     

Comparison of reading speed in normal observers through different forms of equivalent power low vision devices

Compensation at near for vision loss can be achieved using a variety of equivalent forms of low vision magnifiers. Each has inherent advantages and disadvantages in terms of field, working distance, etc. We compared the reading speed of 60 trained, normal observers with 4 commonly prescribed types of low vision devices of +12 D equivalent power (spectacles, hand magnifier, stand magnifier, and telemicroscope) to their normal reading speed. Although there was individual variance in performance, reading speed with all the devices was generally within 20% of normal reading speed. Implications are that in terms of differences in reading speed for normals, the form of the low vision device is not as significant as acquiring proficiency in the use of the selected device.     

Consensus statement on indications for anti-angiogenic therapy in the management of corneal diseases associated with neovascularisation: outcome of an expert roundtable

The cornea is the clear window at the front of the eye and is the eye's main refractive medium. Its transparency is essential for vision. Corneal neovascularisation is a common clinical problem with serious consequences for vision; it can compromise corneal transparency and plays a major role in corneal graft rejection by breaching corneal immune privilege. In this review, we formulate a consensus on the unmet medical needs in the management of corneal neovascularisation and outline a framework for the clinical research that is needed to identify suitable agents to meet these needs.     

Primary success with low vision aids in age-related macular degeneration.

The benefit obtained from various low vision aids (LVAs) was studied in 65 consecutive patients with atrophic (70.3%) or disciform (29.7%) age-related macular degeneration (ARMD). 13.8% were able to read newsprint with age-related reading correction under proper lighting conditions. The primary success achieved with LVAs was good, 91.4% of patients being able to read newsprint. In most cases a simple magnifier (52.3%), high-powered reading glasses (10.8%) or Fonda's glasses (12.8%) were sufficient. The magnification preferred was 5x or less in 25.6% and greater than 5x to 9x in 48.8%. Patients with disciform degeneration required higher magnification than those with atrophic degeneration. It is concluded that most patients with ARMD found low vision aids useful for reading purposes and that a simple optical device was sufficient to achieve reading vision.     

The impact of cataract surgery on patients from a low-vision clinic

Objective

To evaluate the effects of cataract extraction with intraocular lens implantation (CE-IOL) in low-vision patients.

Design

Prospective, interventional case series.

Participants

Twenty low-vision patients (30 eyes) underwent CE-IOL by 1 surgeon at an academic institution.

Methods

Pre- and post-CE-IOL visual acuities and responses to a 23-page survey (self-reported functioning in general vision, mobility, illumination, and ability to see faces) were compared.

Results

Sixteen patients had age-related macular degeneration (AMD); 1 patient each had rod-cone dystrophy, oculocutaneous albinism, retinitis pigmentosa, or cerebrovascular accident. The average age was 78 years (range: 53-96 years). Preoperative best-corrected visual acuity (BCVA) ranged from 20/70 to count fingers; postoperative BCVA at 8 weeks was 20/40 to 20/400, with improvement in 25 (83%) eyes of 15 patients, and no change in the rest. The average change in logMAR of BCVA in the 1 eye or in the eye with better preoperative vision in bilateral surgery was an improvement of 0.6 logMAR units (p = 0.0001). Seventeen (85%) patients noted an improvement in visual function and would consent to CE-IOL again. Twelve patients completed the survey pre- and post-CE-IOL at 3 months. More patients could read with a magnifier after surgery. On average, self-reported functioning was improved.

Conclusions

In this small study, CE-IOL offered subjective and objective benefits to patients from a low vision clinic, many of whom may have been dissuaded from CE-IOL. Most patients had moderately dense cataracts and moderate to advanced AMD, and these features may help form clinical recommendations. Expectations are important to elicit preoperatively. Postoperatively, patients may be more receptive to low-vision services and devices when the prognosis for visual rehabilitation is better.     

A retrospective study of low-vision cases in an Indian tertiary eye-care hospital

PURPOSE: To obtain data on the characteristics of low-vision patients seen at a tertiary eye care hospital in India. METHODS: Records of 410 patients were retrospectively reviewed at the Centre for Sight Enhancement, L.V. Prasad Eye Institute, Hyderabad, India. Patient underwent a comprehensive clinical low-vision examination. Data obtained included age, gender, consanguinity, visual acuity, visual fields, ocular conditions causing low vision and types of low-vision devices and methods prescribed. RESULTS: Two hundred and ninety seven (72%) of 450 patients were male. One-fifth were in the 11-20 years age group (21%). Visual acuity in the better eye was < 6/18-6/60 in almost half these patients (49.3%). One hundred and twenty two patients (29.9%) referred with a visual acuity of > or = 6/18, either had difficulty in reading normal print or had restricted visual fields. The main causes for low vision were: retinitis pigmentosa (19%), diabetic retinopathy (13%), Macular diseases (17.7%), and degenerative myopia (9%). Visual rehabilitation was achieved using accurate correction of ametropia (174 patients), approach magnification (74 patients) and telescopes (45 patients) for recognising faces, watching television and board work. Spectacle magnifiers (187 patients), hand/stand magnifiers (9 patients), closed-circuit television (3 patients), overhead illumination lamp (143 patients) and reading stand (24 patients) were prescribed for reading tasks. Light control devices (146 patients) were used for glare control, and cane (128 patients) and flashlight (50 patients) for mobility. Patients were trained in activities to improve their daily living skills, (54 patients); counselled in environmental modification (144 patients) and ancillary care (63 patients) for educational and vocational needs. CONCLUSION: Data obtained from this study elucidates the characteristics of low-vision patients. This information is likely to help in the development of appropriate low vision services.     

Effects of Magnifier Training: Evidence from a Camera Built in the Magnifier

Purpose: This study evaluated the effect of an evidence-based magnifier training on viewing behavior in visually impaired children aged 3 to 6½ years.

Methods: Effects of a training with a stand magnifier were evaluated by analyzing recordings of 21 visually impaired children, obtained from a miniature camera mounted in the magnifier. In a pre-test, post-test design, 11 of the children trained without magnifier and 10 children trained with magnifier. Three measures were compared from pre- to post-test assessment: 1) observation time in seconds through the magnifier during task performance; 2) the eye that was used during task performance with the magnifier (right eye/left eye as recorded by the camera); and 3) the self-chosen eye-to-chart distance (in cm) in near visual acuity measurement.

Results: Three important changes were found by analyzing the eye-camera recordings: (1) There was a significant shift in average observation time (i.e., the duration of looking through the magnifier in a single glance), before and after training. In the pre-test children used less than 10 s for a glance through the magnifier, whereas in the post-test this was 10–30 s.

(2) In 5 children there was no preference with respect to the number of glances through the magnifier with right or left eye during pre-test measurement. However, such a task-specific dominance was clearly observed in this subgroup after training (post-test measurement).

(3) The eye-to-chart distance, as measured during near-vision testing with LH-single and LH-line test, decreased significantly over the training period (from 9.5 cm to 7.9 cm, pre- to post-test).

There were no differences in the outcome measures between the with-magnifier and without-magnifier training groups. We can conclude that (1) the magnifier training had a positive effect on viewing behavior and the development of dominance, and (2) camera observations provide valuable data on children’s viewing behavior.     

Needs analysis for teachers of the visually impaired

The needs of educators dealing with low vision children were assessed by use of a mailed questionnaire. Teachers of the visually impaired (VH) of the Los Angeles City, Los Angeles County, and Long Beach City districts comprised the sample population. Analysis of the results revealed unmet needs in the following areas: teachers' knowledge in use of low vision aids, lack of low vision assessment by vision care specialists for their students, difficulty with adequacy of eye reports, and lack of communication with their students' eye care specialists. Recommendations are made for improvement of these problem areas.     

Low vision in east African blind school students: need for optical low vision services.

AIMS--There is increasing awareness of the needs of children with low vision, particularly in developing countries where programmes of integrated education are being developed. However, appropriate low vision services are usually not available or affordable. The aims of this study were, firstly, to assess the need for spectacles and optical low vision devices in students with low vision in schools for the blind in Kenya and Uganda; secondly, to evaluate inexpensive locally produced low vision devices; and, finally, to evaluate simple methods of identifying those low vision students who could read N5 to N8 print after low vision assessment. METHODS--A total of 230 students were examined (51 school and 16 university students in Uganda and 163 students in Kenya, aged 5-22 years), 147 of whom had a visual acuity of less than 6/18 to perception of light in the better eye at presentation. After refraction seven of the 147 achieved 6/18 or better. Eighty two (58.6%) of the 140 students with low vision (corrected visual acuity in the better eye of less than 6/18 to light perception) had refractive errors of more than 2 dioptres in the better eye, and 38 (27.1%) had more than 2 dioptres of astigmatism. RESULTS--Forty six per cent of students with low vision (n = 64) could read N5-N8 print unaided or with spectacles, as could a further 33% (n = 46) with low vision devices. Low vision devices were indicated in a total of 50 students (35.7%). The locally manufactured devices could meet two thirds of the need. CONCLUSION--A corrected distance acuity of 1/60 or better had a sensitivity of 99.1% and a specificity of 56.7% in predicting the ability to discern N8 print or better. The ability to perform at least two of the three simple tests of functional vision had a sensitivity of 95.5% and a specificity of 63.3% in identifying the students able to discern N8 or better.