The Relationship Between Cognitive Status and Known Single Nucleotide Polymorphisms in Age-Related Macular Degeneration.

Recent literature has reported a higher occurrence of cognitive impairment among individuals with Age-related Macular Degeneration (AMD) compared to older adults with normal vision. This pilot study explored potential links between single nucleotide polymorphisms (SNPs) in AMD and cognitive status. Individuals with AMD (N = 21) and controls (N = 18) were genotyped for the SNPs CFHY402H, ARMS2A69S and FADS1 rs174547. Cognitive status was evaluated using the Montreal Cognitive Assessment. The two groups differed significantly on which subscales were most difficult. The control group had difficulty with delayed recall while those with AMD had difficulty on delayed recall in addition to abstraction and orientation. Homozygous carriers of the FADS1 rs174547 SNP had significantly lower scores than heterozygotes or non-carriers on the MoCA. The results suggest that the FADS1 SNP may play a role in visual impairment/cognitive impairment comorbidity as reflected in the poorer cognitive scores among homozygotes with AMD compared to those carrying only one, or no copies of the SNP.

Effects of Lighting on Reading Speed as a Function of Letter Size.

OBJECTIVE: We sought to determine under what conditions brighter lighting improves reading performance. METHOD: Thirteen participants with typical sight and 9 participants with age-related macular degeneration (AMD) read sentences ranging from 0.0 to 1.3 logMAR under luminance levels ranging from 3.5 to 696 cd/m². RESULTS: At the dimmest luminance level (3.5 cd/m²), reading speeds were slowest at the smaller letter sizes and reached an asymptote for larger sizes. When luminance was increased to 30 cd/m², reading speed increased only for the smaller letter sizes. Additional lighting did not increase reading speeds for any letter size. Similar size-related effects of luminance were observed in participants with AMD. CONCLUSION: In some instances, performance on acuity-limited tasks might be improved by brighter lighting. However, brighter lighting does not always improve reading; the magnitude of the effect depends on the text size and the relative changes in light level.

Critical success factors in awareness of and choice towards low vision rehabilitation.

PURPOSE: The goal of the current study was to examine the critical factors indicative of an individual's choice to access low vision rehabilitation services. METHODS: Seven hundred and forty-nine visually impaired individuals, from the Montreal Barriers Study, completed a structured interview and questionnaires (on visual function, coping, depression, satisfaction with life). Seventy-five factors from the interview and questionnaires were entered into a data-driven Classification and Regression Tree Analysis in order to determine the best predictors of awareness group: positive personal choice (I knew and I went), negative personal choice (I knew and did not go), and lack of information (Nobody told me, and I did not know). RESULTS: Having a response of moderate to no difficulty on item 6 (reading signs) of the Visual Function Index 14 (VF-14) indicated that the person had made a positive personal choice to seek rehabilitation, whereas reporting a great deal of difficulty on this item was associated with a lack of information on low vision rehabilitation. In addition to this factor, symptom duration of under nine years, moderate difficulty or less on item 5 (seeing steps or curbs) of the VF-14, and an indication of little difficulty or less on item 3 (reading large print) of the VF-14 further identified those who were more likely to have made a positive personal choice. Individuals in the lack of information group also reported greater difficulty on items 3 and 5 of the VF-14 and were more likely to be male. CONCLUSIONS: The duration-of-symptoms factor suggests that, even in the positive choice group, it may be best to offer rehabilitation services early. Being male and responding moderate difficulty or greater to the VF-14 questions about far, medium-distance and near situations involving vision was associated with individuals that lack information. Consequently, these individuals may need additional education about the benefits of low vision services in order to make a positive personal choice.

Canadian ophthalmologists' opinions concerning complementary and alternative medicine (CAM) use in glaucoma.

PURPOSE: Our goal is to investigate the opinion and practice pattern of Canadian ophthalmologists regarding the use of and recommendations for complementary and alternative medicine (CAM) for their glaucoma patients. METHODS: Institutional review board approval for this prospective, cross-sectional survey was obtained from the Research Ethics Board of Sunnybrook Health Sciences Centre. The survey was sent to all ophthalmologists in Canada electronically through the e-mail lists of 4 ophthalmology associations. RESULTS: A total of 241 ophthalmologists representing all provinces in Canada responded to the questionnaire. Twenty-two percent felt that CAM does have a role in glaucoma therapy with specialists being more likely to believe there is a role (P<0.05). Of the total respondents, 26% ask their patients if they use CAM with those in practice for <20 years more likely to encourage use (P<0.05). Of the respondents, 9% recommend CAM and if an ophthalmologist was in practice for <20 years he/she was significantly more likely to recommend CAM (P<0.01). Respondents (62%) in general do not discourage CAM with younger ophthalmologists (younger than 50 y, P<0.02) and ophthalmologists in practice for <20 years (P<0.05) being less likely to discourage CAM use. Respondents (41%) believe that CAM rarely ever affects compliance with ophthalmologists from an urban practice (P<0.01) and academic practice (P<0.05) more likely to deny effect on compliance. Respondents believe that CAM sometimes (46%) results in patient morbidity with ophthalmologists being in practice for <20 years believing that morbidity is less likely (P<0.05). CONCLUSION: A substantial minority of respondents believe that CAM has a role in glaucoma therapy, recommend its use, and ask their patients if they use CAM. Younger doctors are more likely to encourage alternatives; those in practice for <20 years are more likely to ask about alternative medicine use, recommend its use, and believe that morbidity usually does not result from the use of alternative treatments.

Overcoming barriers to low-vision rehabilitation services: improving the continuum of care.

OBJECTIVE: Low-vision rehabilitation is beneficial for patients with uncorrectable vision impairment, specifically in tasks such as reading and activities of daily living. However, referral to and use of these services remain less than optimal. Inspired by the findings of the Montreal Barriers Study, this article reports on an alternative way of introducing low-vision rehabilitation to clients within an ophthalmology department through the presence of an optometrist. DESIGN: The Department of Ophthalmology at the Jewish General Hospital and the 2 Montreal low-vision rehabilitation agencies established a shared satellite office within the department to overcome administrative barriers, reduce the need for travel, and provide services within a familiar environment for patients. PARTICIPANTS: From June 2011 to December 2012, 35 patients with low vision were seen by 1 of the optometrists within the ophthalmology department. METHODS: The optometrist was available on a part-time basis for a total of 20 half days. RESULTS: Seven patients (20%) were already clients of a rehabilitation agency and were seen for follow-up, whereas 3 (9%) did not qualify for rehabilitation based on their level of visual function. A further 6 patients (17%) were treated whereby their needs were met within that appointment, and 19 clients (54%) received initial examination and were referred to the rehabilitation agency for additional services. CONCLUSIONS: The presence of a vision rehabilitation agency in an ophthalmology department through its optometrists helps triage patients, increases the integration of this service, and facilitates the continuum of care. Further fine-tuning will focus on increasing staff awareness and expansion of assistive technologies available at the satellite office.

Barriers to low vision rehabilitation: the Montreal Barriers Study.

PURPOSE: One objective of the Montreal Barriers Study was to examine demographic characteristics of people with vision impairment that may hinder their referral or decision to access rehabilitation services. METHODS: Data collection was conducted in three phases, whereby during phase I, patients in ophthalmology department waiting rooms underwent a structured interview to ascertain demographic variables that may be related to their utilization of the rehabilitation process. Phase II examined variables recorded in the rehabilitation agency file of those who had made the choice to access services. Phase III examined the rehabilitation access behavior of those participants who were referred as part of phase I. RESULTS: In phase I, 54% of the 702 participants had been referred to and received rehabilitation services. An additional 13% were aware of these services but chose not to access them, whereas 33% were unaware of their existence. The variables associated with positive access choice were education, diagnosis, race, acuity at the time of interview, and living situation. In phase II, it was found that acuity at agency intake was markedly better than at the study interview. Of the participants who were referred to rehabilitation services as part of the phase I protocol, it was found in phase III that only 56% had engaged in rehabilitation services. CONCLUSIONS: It seems that even under ideal referral situations, there remain barriers to vision rehabilitation services that have not been specifically identified in the present study. Further research is necessary on the psychological and psychosocial contributors to this process.

Spatial judgments in patients with retinitis pigmentosa.

Previous investigations into cortical plasticity in the presence of ocular disease have focused on central retinal damage. Perceptually, patients often report distortions of visual space which can be partially explained by perceptual filling-in. The mechanisms involved could also apply to peripheral field loss. Spatial interval discrimination was tested in 28 retinitis pigmentosa (RP) patients and a control group. When stimuli were presented to both hemispheres, bias did not differ whereas threshold was poorer in RP patients. When presenting the task to only one hemifield, bias was related to field asymmetry, but only in the left visual field, r(2)=.59. Brain laterality may be an important factor when examining changes in cortical function in response to peripheral system damage.

Health-related and subjective quality of life of older adults with visual impairment.

PURPOSE: To document health-related quality of life (HRQOL) and subjective quality of life (SQOL) and explore their correlates in older adults seeking services for visual impairment (VI). METHOD: A convenience sample of 64 participants (79.3 +/- 5.9 years) with VI was interviewed at home. HRQOL was measured with the Visual Function Questionnaire-25 and SQOL with the Quality of Life Index. The potential correlates were as follows: personal factors (sociodemographic characteristics, co-morbidity, depressive symptoms, activity level), environmental factors (technical aids, social support) and participation in daily activities and social roles (level and satisfaction). RESULTS: Compared to normative data from previous studies of older adults, the participants had lower HRQOL but similar SQOL. Greater level of participation in social roles, higher perceived activity level, use of a writing aid and greater satisfaction with participation in social roles together explained better HRQOL (R2 = 0.66). Fewer depressive symptoms, greater satisfaction with participation in social roles and with social support and fewer co-morbidities together explained better SQOL (R2 = 0.70). CONCLUSIONS: HRQOL of older adults with VI is mainly explained by level of participation correlates, while their SQOL is mainly explained by depressive symptoms and satisfaction variables. The results also underscore the importance of social roles for HRQOL and SQOL of this population.

Beyond visual acuity: functional outcome and patient satisfaction following treatment for age-related macular degeneration.

OBJECTIVE: The success of current medical treatments for choroidal neovascular membranes secondary to age-related macular degeneration (AMD) has often been determined anatomically by change in lesion size and cessation of leakage. Measuring the functional success of treatments has most often revolved around visual acuity and has seldom encompassed patients' satisfaction with treatment. Using additional objective and subjective measures to assess the outcome of treatments may provide greater insight into the visual functions that are lost, maintained, or improved during the course of treatment. STUDY DESIGN: Cross-sectional study. PARTICIPANTS: Forty-six patients diagnosed with exudative AMD. Participants had received at least 1 photodynamic therapy (PDT) treatment at the time of testing (mean 3.0, SD 1.9). METHODS: Objective tests of visual function (Snellen, Early Treatment Diabetic Retinopathy Study, Minnesota Low-Vision Reading Test, Contrast Sensitivity, Face Acuity) and a subjective questionnaire, the Visual Function-14 (VF-14) were administered to all patients. Treating ophthalmologists completed a 3-item questionnaire. RESULTS: No objective measures of visual function correlated with patient satisfaction or with the ophthalmologists' evaluation of treatment success. The VF-14 was not related to the ophthalmologists' evaluation of treatment outcome. Similarly, patient satisfaction was unrelated to the ophthalmologists' assessment of treatment success. A correlation was found between the VF-14 and patient satisfaction, r = 0.50, p < 0.05. CONCLUSIONS: Objective measures of visual function do not necessarily reflect the viewpoint of patients regarding PDT treatment outcome. Patients and doctors differ in their interpretation of treatment success and patients' overall satisfaction might best be reflected through a visual function questionnaire.

Participation in daily activities and social roles of older adults with visual impairment.

PURPOSE: (1) to document participation in daily activities and social roles of older adults seeking services for visual impairment (VI) and compare it with that of the older population without VI or other disabilities, and (2) to explore correlates of their participation. METHODS: The 64 participants (46 women) had an average age of 79.3 years (SD = 5.9 years) and presented various types of VI. Participants were interviewed at home to collect information regarding their visual function (National Eye Institute Visual Function Questionnaire-25), sociodemographic and clinical characteristics, including depressive symptoms (Geriatric Depression Scale), and participation (Assessment of Life Habits/LIFE-H). Each participant was matched with another person without disabilities randomly recruited from the community. Results for the two populations on the Life-H participation domains were compared using t-tests. In the group with VI, general information (independent variables) was examined in relation to participation main scores (dependent variables), followed by multiple linear regression analyses. RESULTS: Participation in daily activities and social roles of participants with VI (mean +/- SD (/9) = 6.8 +/- 1.0 and 5.6 +/- 1.6, respectively) was significantly lower than that of participants without VI (8.1 +/- 0.4 and 8.3 +/- 0.4) (p < 0.0001). Depressive symptoms and perceived quality of distance vision were the strongest correlates and together explained more than 65% of the variance in the participation scores of the subjects with VI. CONCLUSIONS: This study demonstrates the participation restrictions associated with VI and underlines the importance of psychological aspects in participation.

Hierarchical linear modeling of visual acuity change over time: rate of functional recovery after macular hole surgery.

PURPOSE: To examine acuity recovery rate after Macular Hole (MH) surgery, using Hierarchical Linear Modeling (HLM) with linear and curvilinear regression analysis. METHODS: Preoperative MH diameter (OCT) and acuity (ETDRS) were recorded in 20 eyes. Acuities were tested during follow-up (6 to 23 months), with three to eight measurements per eye. The resulting 95 acuities were analyzed using HLM. Variability at the level of the person was explained by change over time, using a natural logarithm conversion. Across patients, MH diameter was used to predict slopes and intercepts at the level of the individual. RESULTS: MH diameter was able to account for significant amounts of variability in preoperative acuity (intercept) and significantly influenced rate of functional recovery (slope). A nonlinear approach to the data accounted for the largest amount of variance. CONCLUSIONS: Participants with larger MHs recovered relatively more acuity sooner while eyes with smaller MHs had better absolute acuity outcome. HLM provides important insight into the recovery process after MH surgery and is more flexible with follow-up data. In the context of MH treatment, most recuperation occurred during the initial 6 months.

Luminance contrast with clear and yellow-tinted intraocular lenses.

PURPOSE: To determine whether yellow-tinted intraocular lenses (IOLs) negatively affect luminance contrast in postoperative cataract patients. SETTING: Department of Ophthalmology, Sir Mortimer B. Davis Jewish General Hospital, McGill University, Montreal, Quebec, Canada. METHODS: Luminance contrast was measured using the minimum-motion technique. The stimulus consisted of blue and red sinusoidal gratings differing in luminance. Patients had implantation of a clear or yellow-tinted IOL and were tested monocularly 2 to 9 weeks after cataract surgery. No patient had concomitant ocular diseases or congenital color defects, assessed by their ophthalmologist, or flicker-sensitive epilepsy. All patients had a visual acuity of 20/40 or better a mean of 4 weeks+/-2 (SD) postoperatively. RESULTS: Patients ranged in age from 55 to 89 years. An independent-samples Student t test showed that patients with a yellow-tinted IOL had significantly lower luminance contrast values than patients with a clear IOL (P<.05). CONCLUSIONS: The results suggest that yellow-tinted IOLs affect the perception of luminance under photopic conditions. More blue light was required to make luminance judgments with a yellow-tinted IOL than with a clear IOL. Further study of the functional impact of luminance reduction by yellow-tinted IOLs is warranted.

Differences between recognition and resolution acuity in patients undergoing macular hole surgery.

PURPOSE: The present investigation compared recognition acuities (ETDRS chart) with resolution acuities (Landolt-C chart) in a sample of patients with idiopathic macular holes (MH). Traditionally, visual acuity in a clinical setting is measured with a letter chart. Yet, the ability to recognize a letter differs from a resolution task, such as detecting the direction of a gap in a ring. It was hypothesized that resolution acuity would be more impaired than recognition acuity in patients with MH, because component cues in letter optotypes are not available in Landolt-Cs. METHOD: Visual acuities of 23 patients with MH (age range, 52-82) were tested, using standard ETDRS and Landolt-C charts. Optical coherence tomography was used to confirm the diagnosis of MH. RESULTS: Acuities correlated strongly, before and after surgery (r = 0.92 and r = 0.95, respectively). However, paired t-tests determined that resolution acuity was significantly more impaired at both time points than was recognition acuity (P < 0.001). Using Bland-Altman plots, the limits of agreement between the two acuity types indicated that resolution acuity differed from recognition acuity by up to five lines before surgery and up to 3 lines after surgery. CONCLUSIONS: ETDRS and Landolt-C acuities differ in a clinically significant way in patients before and after MH surgery. Measuring recognition acuity by reading letters may lead to an overestimate of visual ability at the retinal level in patients with MH by including compensatory top-down cognitive processes that are unavailable for resolution tasks.

Macular hole: perceptual filling-in across central scotomas.

The present study examined perceptual distortions of a vertical line before and after macular hole (MH) surgery in 25 eyes of 24 patients. Participants' perceptual reports of distortions were classified as solid, bent right/left, thinned at the center, or broken. The majority of patients (72%) reported symmetrical distortions of the line pre-operatively. After surgery, participants with larger MHs were more likely to retain residual distortions. Of particular interest is the group reporting thinning of the line preoperatively, as the center should be perceptually missing. Examination of MH diameters in relation to the line perceptions indicated that the shape of the perceived line can be explained at the retinal level, while its continuity must be perceptually created at the cortical level.

Defining the nature of motion perception deficits in glaucoma using simple and complex motion stimuli.

PURPOSE: The purpose of this study is to determine the nature of motion perception deficits in primary open-angle glaucoma by measuring the sensitivity of simple (luminance-defined) and complex (texture-defined) motion, the latter requiring supplementary neural processing to be resolved. These findings will help address the possible extent of the cortical damage in glaucoma that has been recently demonstrated by anatomic and physiological studies. They also serve the purpose of establishing which motion paradigms would be most appropriate for assessing glaucoma-related functional loss. METHODS: Direction-identification thresholds for first-order and second-order motion were measured for 26 patients with primary open-angle glaucoma (for both phakic and pseudophakic) and 18 nonglaucomatous observers. RESULTS: The glaucomatous observers showed significantly increased motion thresholds for both first- and second-order motion conditions when compared with nonglaucomatous observers. However, the relative increase in threshold for first-order motion did not differ significantly from that of second-order motion. CONCLUSIONS: These findings imply that there is no measurable higher-level cortical function damage caused by the glaucomatous process because no greater loss in second-order motion was observed. Based on the results, we suggest that motion paradigms used to assess functional loss in primary open-angle glaucoma should consist of simple, first-order type stimuli to minimize potential confounds such as those introduced by both the normal and pathologic aging process on complex motion processing (i.e., perimetry using complex motion stimuli).

Quebec model for low vision rehabilitation.

The increase in longevity (and secondary morbidity) in the Quebec population adds social and financial pressure to society, as it does elsewhere in Canada and in many western countries. This article gives a brief history of the evolution of vision rehabilitation services in Quebec and describes how services are provided for people with low vision throughout the province. Although numerous groups, associations, centres, and resources are available to assist people with vision impairments, such as the Canadian National Institute for the Blind-Québec, the majority of visual rehabilitation services are provided by government-sponsored rehabilitation centres, namely the Centres régionaux de réadaptation en déficience physique that are located strategically throughout the province. Low vision clinical evaluations in these centres are shared by 36 optometrists throughout the province. Between 5 and 7 ophthalmologists are involved in low vision care, half in university-affiliated hospitals, primarily in Montreal. There may be delays of up to 6 months to be seen in a funded low vision clinic. Statistics obtained from la Régie de l'assurance maladie du Québec show that there are approximately 8,000 requests for low vision aids every year, and that 80% of clients retain at least some level of visual function. Services are covered by Medicare and low vision aids are provided at no cost, although ophthalmologists cannot prescribe low vision aids through the Medicare-funded system. We must ensure that the capacity of our system continues to provide adequately for clientele in the future.

Visual function assessment and metamorphopsia after macular hole surgery.

The purpose of this study was to develop a new resolution acuity measure for patients after macular hole surgery. Fifty eyes of 44 patients who had undergone successful treatment were tested. Visual acuity was measured with the Snellen, Early Treatment of Diabetic Retinopathy Study and Landolt-C charts. A Line Resolution Test was performed as part of their follow-up exam where a vertical line was presented. Participants were categorized by their perception of the line as solid, bent or broken. The line could be distorted into a sine-wave pattern in order to determine the participants' detection threshold for the distortion. Chart acuities did not differ among the three groups, as categorized by their line perception. Only the distortion measure was sensitive enough to differentiate the solid- from the broken-line group. The distortion measure assesses resolution power of the macula in smaller increments than acuity charts. This hyperacuity approach is more appropriate in the assessment of functional outcome after microsurgery.

Red-green chromatic mechanisms in normal aging and glaucomatous observers.

PURPOSE: This study was designed to determine whether normal aging and glaucoma are associated with red-green (R/G) chromatic processing abnormalities, a function that is primarily performed by the parvocellular visual pathway. METHODS: Chromatic processing mechanisms were examined in 98 glaucomatous observers (between the ages of 49 and 93 years; mean age, 70.8 +/- 9.4 [SD]) and 67 normal observers (between the ages of 49 and 88; mean age, 70.6 +/- 10.6 years) with the use of the minimum-motion and motion-nulling paradigms. Phakic glaucomatous (n = 60; mean age, 68.7 +/- 8.9 years) and normal (n = 32; mean age, 69.8 +/- 10.6 years) and pseudophakic glaucomatous (n = 38; mean age, 74 +/- 9.4 years) and normal (n = 35; mean age, 71.4 +/- 10.6 years) subjects were tested to evaluate the effects of lenticular aging on color perception. RESULTS: Phakic observers (normal or glaucomatous) displayed significantly different minimum-motion values than did both their younger counterparts and all the pseudophakic subjects. These results suggest that normal aging with the presence of a natural lens is accompanied by a significant decrease in green-light sensitivity, an effect that is not exacerbated by glaucoma and is primarily related to optical factors. The data also revealed no differences in color motion perception between groups, indicating that the higher cortical mechanisms of the parvocellular pathway implicated in the analysis of information about the middle and long wavelengths of the visible spectrum are not selectively affected by the disease process and normal aging. CONCLUSIONS: Normal aging and glaucoma do not produce significant R/G chromatic processing deficits at retinal and postretinal levels when optical factors are excluded. The authors propose the hypothesis that glaucoma-related effects on motion perception and blue-on-yellow perimetry should be viewed as evidence of loss of ganglion cells that necessitates integration of information over larger retinal areas and more receptor cells than in the R/G chromatic system. Ganglion cells with large receptive fields involve more neural connections and are less numerous than those that respond to R/G information. The functional consequence of this could be that the loss of a single ganglion cell with a larger receptive field would have a greater impact on visual function than the loss of a ganglion cell with a smaller receptive field, such as the ones that process R/G information. The authors believe that glaucoma-induced functional loss is best viewed as related to receptive field structure and function rather than to anatomic cell-type damage.

The role of lenticular senescence in age-related color vision changes.

PURPOSE: It has been reported that greater age-related losses in sensitivity occur for short-wavelength visual stimuli than for medium- and long-wavelength visual stimuli. The purpose of the current experiment was to determine to what extent optical, receptoral, and postreceptoral factors contribute to these age-related changes in color vision. METHODS: One hundred two observers (ages 18-87) completed a minimum motion task to determine isoluminance between red and green and between red and blue. A motion-nulling task was also performed to assess the L-M postreceptoral chromatic mechanism. RESULTS: No significant age-related changes occurred in red-green isoluminance values. Red-blue isoluminance values showed a significant and systematic decrease with age in observers with phakic eyes. Pseudophakic eyes in older subjects performed this task as well as phakic eyes in young subjects. The motion-nulling results demonstrated small age-related losses in the postreceptoral color mechanisms. CONCLUSIONS: The findings of this experiment, particularly those of the red-blue isoluminance task, indicate that the optical factor of lenticular senescence is the main contributor to the age-related changes observed in color vision. A model based on age-related changes in lenticular absorbance shows good fit with the experimental data of observers with phakic eyes, suggesting that optical factors are the main cause of the age-related changes in these color vision tasks.

Using the arteriolar Pressure Attenuation Index to predict ocular hypertension progression to open-angle glaucoma.

BACKGROUND: Vascular phenomena are considered important to optic nerve and visual field progression in open-angle glaucoma (OAG). A recently described formulation, the Pressure Attenuation Index (PAI), links arteriolar caliber variations to pressure loss along the retinal arteriolar system. OBJECTIVE: To examine whether the PAI could predict ocular hypertension (OHT) progression to OAG. METHODS: The PAI was calculated for 27 eyes of 14 patients with OHT using initial and final digitized optic disc photographs taken during a follow-up interval of 5 to 18 years. Serial stereo color disc photographs and visual fields were analyzed to determine progression. RESULTS: At baseline, the arteriolar tree of 8 subjects with OHT that progressed to OAG (n = 8 eyes) demonstrated a 45.8% greater mean PAI value than that of 7 subjects who did not progress (n = 7 eyes) (mean +/- SEM, 5.31 +/- 0.93 vs 3.64 +/- 0.34; r = 0.83). Progression was independent of baseline cup-disc ratio. The PAI values of subjects with stable OHT remained stable after a median follow-up interval of 12.0 years. The PAI values of subjects with OHT that progressed demonstrated a further increase of 19.97% +/- 11.24% during a median follow-up period of 6.0 years. CONCLUSIONS: The results support the hypothesis that low end-arteriolar pressure predicts the progression from OHT to OAG. The PAI provides a new, early, reproducible, and physiological method to study vascular phenomena in glaucoma.