Samuel N. Markowitz

Principles of modern low vision rehabilitation

Low vision rehabilitation is a new emerging subspecialty drawing from the traditional fields of ophthalmology, optometry, occupational therapy, and sociology, with an ever-increasing impact on our customary concepts of research, education, and services for the visually impaired patient. A multidisciplinary approach and coordinated effort are necessary to take advantage of new scientific advances and achieve optimal results for the patient. Accordingly, the intent of this paper is to outline the principles and details of a modern low vision rehabilitation service. All rehabilitation attempts must start with a first hand interview (the intake) for assessing functionality and priority tasks for rehabilitation, as well as assessing the patients all-important cognitive skills. The assessment of residual visual functions follows the intake and offers a unique opportunity to measure, evaluate, and document accurately the extent of functional loss sustained by the patient from disease. An accurate assessment of residual visual functions includes assessment of visual acuity, contrast sensitivity, binocularity, refractive errors, perimetry, oculomotor functions, cortical visual integration, and light characteristics affecting visual functions. Functional vision assessment in low vision rehabilitation measures how well one uses residual visual functions to perform routine tasks, using different items under various conditions, throughout the day. Of the many functional vision skills known, reading skills is an obligatory item for all low vision rehabilitation assessments. Results of assessment guide rehabilitation professionals in developing rehabilitation plans for the individual and recommending appropriate low vision devices. The outcome from assessing residual visual functions is detection of visual functions that can be improved with the use of optical devices. Methods for prescribing devices such as image relocation with prisms to a preferred retinal locus, field displacement to primary gaze position, field expansion, and manipulation of light are practiced today in addition to, or instead of, magnification. Correction of refractive errors, occlusion therapy, enhancement of oculomotor skills, and field restitution are additional methods now available for prescribing devices leading to rehabilitation of visual functions. The outcome from assessing residual functional vision is detection of functional vision that can be improved with the use of vision therapy training. After restoration of optimal residual visual functions is achieved with optical devices, one can follow with training programs for restoration of lost vision-related skills. If an optical dispensary is available where prescribing of low vision devices routinely take place, this will help ensure familiarity and specialization of the dispensary and staff with low vision devices and their special dispensing requirements. The dispensing of low vision devices is an opportunity to introduce the device to the patient, train the patient in the correct use of the device for the task selected, and create a direct and continuous connection with the patient until the next encounter. Following assessment, prescribing, and dispensing of devices, a low vision practitioner, ophthalmologist or optometrist, is responsible for recommending and prescribing vision therapy training to improve residual functional vision. An attempt to present a template for a comprehensive modern low vision rehabilitation practice is made here by summarizing scientific developments in the field and stressing the multidisciplinary involvement required for this kind of practice. It is hoped that this paper and other initiatives from colleagues, the public, and government will promote and raise awareness of modern low vision rehabilitation for the benefit of all.

Microperimetry and clinical practice: an evidence-based review

Microperimeters embody technological abilities required to assess components of residual visual functions and functional vision. Residual visual functions and functional vision after macular vision loss are mostly defined by 3 major components: scotoma characteristics, preferred retinal loci (PRLs) and oculomotor control. Microperimetry may be proven superior as a method to standard automated perimetry (SAP) for residual visual function assessment. During microperimetry stimuli are projected directly on the retina with accurate test-retest of the same retinal point monitored by eye tracking technology. Microperimeters offer also abilities to determine accurately the location of a PRL. Recent research reveals also that fixation stability estimates in low vision cases are reliable predictors of visual acuity estimates. Fixation stability estimates provided automatically by the microperimeters are based on proprietary algorithms and provide reasonable estimates very close to BCEA values calculated from raw data. More and more microperimeters are used in clinical retina practice to assess more accurately the impact of diseases or of interventions on the retina. Microperimeters are also in use more often in glaucoma practices and it seems evident that the main usage for microperimeters is destined to monitor glaucoma damaged residual visual functions and functional vision. In addition identification of eccentric location of PRLs and fixation stability estimates at the PRL in low vision patients offers the LVR practitioner the option to use the best residual visual function available for rehabilitation. For mainstream ophthalmology many indicators point to the fact that microperimeters may take the lead role played by SAP in the last decades. For vision rehabilitation practitioners the advent of multiple choices for microperimetry portends the introduction of modern rehabilitation concepts in most clinical practices. Both developments seem to happen sooner, rather than later as expected by most.

Concept of a functional retinal locus in age-related macular degeneration

PURPOSEnPreferred retinal loci used for eccentric fixation in patients with age-related macular degeneration (AMD) may be different from the eccentric neighbouring loci of highest retinal sensitivity. This study was designed to highlight the conceptual difference between the 2 and the concept of a functional retinal locus encompassing both the preferred retinal locus and the locus with highest retinal sensitivity.nnnDESIGNnProspective, nonrandomized, observational case series.nnnPARTICIPANTSnWe recruited 15 adults with documented AMD, low vision, and best-corrected visual acuity of 20/50-20/400 in the better eye.nnnMETHODSnAutomated microperimetry methods were used to assess topographic retinal sensitivity and location of preferred retinal loci.nnnRESULTSnMean (SD) age for the group was 85.1 (6.5) years. Mean (SD) best-corrected visual acuity measured was 0.88 (0.25) logMar units (20/150). The mean (SD) eccentricity of the preferred retinal locus used for fixation was different from the eccentricity of the area with highest retinal sensitivity in the same eye (7.53 degrees [2.47 degrees ] vs 9.30 degrees [2.93 degrees ], respectively; p < 0.0003). The oculomotor efficiency score measured 82%. The mean (SD) retinal sensitivity at the preferred retinal loci was inferior to that of loci with highest retinal sensitivity (5.83 [4.26] vs 8.60 [3.06] dB, respectively; p < 0.0007). The highest correlation was measured between potential visual acuity estimates and estimates of retinal sensitivity at the highest retinal sensitivity loci (p < 0.0048).nnnCONCLUSIONSnPreferred retinal loci and highest retinal sensitivity loci are not identical in AMD cases. A new concept of functional retinal locus is proposed to define their relation. A new concept of an oculomotor efficiency score is proposed to define oculomotor abilities when macular function is lost.

Visual field expansion in patients with retinitis pigmentosa.

BACKGROUNDnTo determine the effectiveness of using spectacle-mounted prisms for field expansion in patients with retinitis pigmentosa (RP).nnnMETHODSnVision-related activities of daily living (V-ADL) questionnaire scores and functional visual field score (FFS) measurements were conducted before and after a one-month trial of spectacle-mounted prisms in those patients with RP who had residual central visual fields of less than 10 degrees.nnnRESULTSn16 patients were recruited who met study inclusion criteria. Mean V-ADL and FFS at baseline were 67.6 (73%) and 22.9 (46%), respectively. After a 1-month trial using spectacle-mounted prisms, V-ADL and FFS demonstrated significant improvement to 73.4 (80%, p < 0.05) and 27.0 (54%, p < 0.001), respectively.nnnINTERPRETATIONnSpectacle-mounted prisms effectively create visual field expansion and noticeable spatial orientation benefits in patients with RP. This may provide an adjunctive tool in low vision rehabilitation and should be considered in all cases with RP with less than 10 degrees of visual field.

Image relocation with prisms in patients with age-related macular degeneration

BACKGROUNDnTo determine the benefits of image relocation (IR) with prisms in patients with age-related macular degeneration (AMD).nnnMETHODSnThis was a retrospective comparative interventional case series of 100 patients with AMD and 5 years of available follow-up records. Participants underwent complete low vision (LV) assessments, including identification of preferred retinal locus (PRL). Prisms were added to prescription glasses to produce IR to the presumed PRL. Main outcome measures were best-corrected visual acuity (BCVA), location of the PRL preferred by the patient for rehabilitation, use of glasses prescribed, and number of prism diopters prescribed.nnnRESULTSnPatients wearing prescribed glasses for distance with prisms for IR showed improved BCVA (t(63) = 9.5, p = 0.001) as did those patients wearing prescribed glasses for distance without prisms for IR (t(14) = 2.25, p = 0.04). Patients wearing prescribed glasses for distance with prisms for IR achieved better BCVA than those patients wearing prescribed glasses for distance without prisms for IR (t(77) = 2.0, p = 0.05). Patients reported using distance glasses with prisms for 3 to 48 months (mean [SD], 8.4 [11.7] mo). Number of prism diopters used (mean [SD], 5.8 [1.9] D) was well tolerated by all patients. PRL preferred by patients was on the upper retina in 98.5% of cases.nnnINTERPRETATIONnIR with prisms to PRL in patients with AMD results in a significant and sizable improvement in BCVA. This effect is probably created by facilitation of oculomotor functions resulting from direct reduction of fixation instability.

The use of prisms for vision rehabilitation after macular function loss: an evidence-based review.

To determine the efficacy of prisms used for redirection of incoming images towards the peripheral retina in cases with macular function loss. Meta‐analysis of published work reporting outcomes from interventions using prisms was performed. The primary outcome measure selected for analysis was visual acuity (VA) used for viewing distance targets. Pooled data from 449 cases where prisms were prescribed for wearing in distance glasses were analysed. Visual acuity was better after using prisms (1.05 versus 0.89 logMAR units, pu2003<u20030.044). Mean effect size for improving VA was 79 bigger than the effect size calculated for the control group (0.158 versus 0.002). Most patients (76%) reported compliance with the therapy and also reported other benefits directly derived from the realized VA improvement. Published studies collectively offer positive evidence in support of using prisms for low vision rehabilitation after macular function loss. Further research is required to reach definitive binding conclusions.

Scotoma size reduction as an adaptive strategy in age-related macular degeneration

OBJECTIVEnRetinal areas with reduced sensitivity to light stimuli represent the true scotoma size in patients with age-related macular degeneration (AMD), whereas the perceived visual field defect area that covers a specific target of regard may represent an effective size of the same scotoma. This study was designed to highlight the conceptual difference between the true scotoma size and its effective scotoma size counterpart.nnnDESIGNnProspective nonrandomized observational case series.nnnPARTICIPANTSnTen adults with documented AMD, low vision, and best-corrected visual acuity of 20/50-20/200 in the better eye.nnnMETHODSnEffective scotoma size and true scotoma size were calculated from measurements with the macular grid test performed with automated perimetry and from microperimetry performed with the Nidek MP-1, respectively.nnnRESULTSnTen patients aged 70-92 years (mean 81 years) met the inclusion criteria. Mean effective scotoma size measured with the macular grid test was 40.19 (SD 34.88) deg2. Mean true scotoma size measured with microperimetry was 75.17 (SD 56.08) deg2 (p < or = 0.003). The log unit change in scotoma size, defined as scotoma utility score, was -55.91%. The effect size observed for the scotoma utility score was 0.74.nnnCONCLUSIONSnEffective scotoma size experienced by patients with AMD is significantly smaller than true scotoma size. This reduction may be explained by adaptive variability in eye positions during any single fixation stability attempt, which ultimately results in enhanced visual field perception.

Canadian research contributions to low-vision rehabilitation

BACKGROUNDnDemographic changes likely to occur in the near future and the need for planning to address them are behind the urgent drive to assess present-day provision and utilization of low-vision rehabilitation (LVR) services in the community. Perhaps even more important is the assessment of supporting research work in this field of health care. The purpose of this study, therefore, was to investigate the current involvement of researchers in Canada in the elucidation of the LVR sciences.nnnMETHODSnA PubMed search of the MEDLINE database was performed. Publications were identified according to preset criteria and search key words pertinent to various aspects of LVR sciences. Data were collected on the corresponding authors and their affiliations, type of journal and type of study performed, and reported outcome measures.nnnRESULTSnApproximately 1500 papers were reviewed, and 131 that met the preset criteria were included in the study. Medical doctors published most papers (48.1%), followed by optometrists, those with PhDs, occupational therapists, and others; most of the papers (44.3%) were published in ophthalmology journals. Research was performed mainly at Canadian universities (84%), and the findings were published in the last 3 decades. The studies largely concentrated on rehabilitation services and other aspects of vision rehabilitation (55%), whereas studies focusing on the evaluation of tools used for assessment of either visual functions or functional vision were in the minority (45%).nnnINTERPRETATIONnThe majority of research activity in Canada is university based and involves the medical profession in a leading role, thus affording LVR the appropriate medium for promotion and development of a multidisciplinary approach to outstanding research issues. Only a fraction of current research in LVR (12.2%) deals with outcome measures of the therapeutic interventions aimed at restoring functional vision.

Residual stereopsis in age-related macular degeneration patients and its impact on vision-related abilities: A pilot study

OBJECTIVEnTo determine the effect of residual stereopsis on vision-related abilities of low vision (LV) patients with age-related macular degeneration (AMD).nnnMETHODSnProspective non-randomized observational case series. Inclusion criteria included documented AMD, LV with best corrected visual acuity (BCVA) of 20/50-20/400 in the better eye, and ages between 50 and 90 years. Stereoacuity was measured using the near Frisby Stereotest. Vision related abilities were documented with the VA LV VFQ-48 questionnaire.nnnRESULTSnTwenty-seven subjects with mean age of 84±6 years old were recruited, of which 59.3% (16/27) were female. 59.3% (16/27) of the subjects were not able to see any stereoacuity plate, 25.9% (7/27) had stereoacuity of 340s of arc (SOA), 11.1% (3/27) had stereoacuity of 170 SOA and 3.7% (1/27) had stereoacuity of 85 SOA. The mean Overall Functional Visual Abilities (OFVA) score was significantly higher in those with stereopsis (2.25±0.99) than those without stereopsis (1.50±0.92) (P=0.028).nnnCONCLUSIONSnLV patients with stereopsis have better OFVA than those without. Stereopsis should be considered as a component of LV rehabilitation and considered as an outcome measure in research and clinical practice.

Use of prisms for vision rehabilitation after macular function loss may impact oculomotor control

OBJECTIVEnTo determine the effect from using prisms for image relocation on fixation stability estimates in low-vision (LV) patients with age-related macular degeneration (AMD).nnnMETHODSnThe study was designed as a prospective, nonrandomized, observational case series. Inclusion criteria included documented AMD, LV with best corrected visual acuity of 20/50 to 20/400 in the better eye, and cases wearing distance glasses with prisms for image relocation incorporated in the glasses. Preferred retinal locus (PRL) and fixation stability were assessed using the Nidek MP1 and MAIA microperimeters. A control group was used to compare results.nnnRESULTSnWe recruited 14 study subjects with AMD and 10 with no retinal pathology serving as a control group. On average, 6 (SD 2) prisms diopters were prescribed to all in distant viewing glasses. Fixation stability was better at 3-month interval from baseline (p = 0.021) in the AMD group and stayed the same for the following 9 months. No change in fixation stability was noticed in the control group. There was no statistically significant difference in PRL eccentricity between the 3- and 12-month intervals in the AMD group (p = 0.39). However, there was a positive correlation between PRL eccentricity and baseline bivariate contour ellipse area in the AMD group (p = 0.052).nnnCONCLUSIONSnPatients with LV with AMD who are using prisms for image relocation toward the peripheral retinal exhibit better fixation stability than those who are not using prisms. Better fixation stability may impact on other visual outcomes. Use of prisms should be considered in any LV rehabilitation attempt and used in conjunction with other modern interventions in LV rehabilitation.