- Email: [email protected]
Re: Lee et al.: Evaluating access to eye care in the contiguous United States by calculated driving time in the United States Medicare population (Ophthalmology. 2016;123:2456-2461)
Correspondence 3. Koktekir BE, Gedik S, Bakbak B. Bilateral severe anterior uveitis after unilateral selective laser trabeculoplasty. Clin Experiment Ophthalmol. 2013;41(3):305-307.
Re: Lee et al.: Evaluating access to eye care in the contiguous United States by calculated driving time in the United States Medicare population (Ophthalmology. 2016;123:2456-2461) Lee et al1 state, “Our findings contrast with the results of Gibson,2 who analyzed 3143 counties in the United States and found that 24.1% of the counties were in the lower 2 quartiles of ophthalmologist availability but in the upper 2 quartiles of optometrist availability.” Gibson2 created population-weighted quartiles of the county-level number of ophthalmologists per capita and the county-level number of optometrists per capita. Lee et al1 maintain that “this method of analysis grossly underestimates availability.” This letter argues that Lee et al1 did not support these assertions and notes that it has not been established that driving time to the closest eye care provider, the measure of provider availability used by Lee et al,1 is a better predictor of vision health outcomes than other measures of the availability of eye care providers. To the first point, Lee et al1 did not present findings about the number of geographic areas with a combination of “lower” ophthalmologist availability and “higher” optometrist availability or the percentage of the population that lived in these types of areas; therefore, it is not possible to directly compare their findings with those of Gibson.2 Additionally, Lee et al1 presented no empirical evidence to support the statement that provider density measures grossly underestimate availability. Their critique that county-level provider density measures do not consider the proximity of ophthalmologists and optometrists in neighboring counties is well-taken and is also mentioned as a caveat by Gibson,2 but the validity of this point does not necessarily mean that countylevel provider density measures grossly underestimate availability. Lee et al1 estimated that >90% of US Medicare beneficiaries lived within a 30-minute drive of an ophthalmologist and within a 15-minute drive of an optometrist. Driving time may be misestimated for some residents of rural areas, because census block groups can be very large in rural areas and the estimates of Lee et al1 are based on the distance from the geographic center of an individual’s census block group of residence rather than on the distance from the precise location of an individual’s residence. Drawing on 2010 decennial census data to provide examples of the frequency and geographic distribution of large census block groups, 97 of 413 block groups in Wyoming, 941 of 15 814 block groups in Texas, and 310 of 4489 block groups in Wisconsin were >50 square miles. Based on 2010 decennial census data, 22.4% of the US population aged 65 years lived in a rural area. The number of providers per capita in a geographic area can be thought of as a rough measure of both provider proximity and provider capacity. Driving time to the closest eye care provider does not capture the capacity of providers to take on additional patients or to see existing patients in a timely fashion. Lee et al could use their data to create a measure of eye care provider capacity by calculating for each US Medicare beneficiary how many other TO THE EDITOR:
Medicare beneficiaries had the same closest provider. They could examine how this measure varied for residents of different regions of the country and for residents of rural and urban areas, and they could examine the extent to which the driving time and provider capacity measures offered consistent views on the degree of eye care provider availability. Previous research in the United States has found that measures of eye care providers per capita were significantly associated with vision health outcomes in empirical models that included a large set of controls for individual and contextual characteristics, providing evidence on the predictive validity of provider density as a measure of the availability of eye care providers.3e5 Although it stands to reason that driving time measures of eye care provider availability would be similarly associated with vision health outcomes, to my knowledge this association has yet to be examined. Until the superior predictive validity of driving times has been established, the question of which measure is the best measure of the availability of eye care providers remains unsettled.
DIANE GIBSON, PHD Marxe School of Public and International Affairs, Baruch College, City University of New York, New York, New York
Financial Disclosures: The author has no proprietary or commercial interest in any materials discussed in this article. Available online: May 22, 2017. Correspondence: Diane Gibson, PhD, Marxe School of Public and International Affairs, Baruch College - CUNY, 17 Lexington Avenue, Box D-901, New York, NY 10010. E-mail: [email protected].
References 1. Lee CS, Morris A, Van Gelder RN, Lee AY. Evaluating access to eye care in the contiguous United States by calculated driving time in the United States Medicare population. Ophthalmology. 2016;123:2456-2461. 2. Gibson D. The geographic distribution of eye care providers in the United States: implications for a national strategy to improve vision health. Prev Med. 2015;73:30-36. 3. Chou C, Zhang K, Crews J, et al. Impact of geographic density of eye care professionals on eye care among adults with diabetes. Ophthalmic Epidemiol. 2012;19:340-349. 4. Gibson D. Eye care availability and access among individuals with diabetes, diabetic retinopathy, or age-related macular degeneration. JAMA Ophthalmol. 2014;132:471-477. 5. Gibson D. The local availability of eye care providers and the vision health of adults in the United States. Ophthalmic Epidemiol. 2016;23(4):223-231. We sincerely thank Dr Gibson for her comments on our recent article concerning access to eye care providers.1 Dr Gibson notes that we have used a novel metricdshortest driving distancedas a proxy for access to care, and that comparisons of this metric with existing methodologies, such as county-level provider data studied by her own group, are difficult. We concur with this assessment, but wish to highlight ways in which we feel the current metric may differ from county-level provider data. REPLY:
e65
Re: Lee et al.: Evaluating access to eye care in the contiguous United States by calculated driving time in the United States Medicare population (Ophthalmology. 2016;123:2456-2461) Lee et al1 state, “Our findings contrast with the results of Gibson,2 who analyzed 3143 counties in the United States and found that 24.1% of the counties were in the lower 2 quartiles of ophthalmologist availability but in the upper 2 quartiles of optometrist availability.” Gibson2 created population-weighted quartiles of the county-level number of ophthalmologists per capita and the county-level number of optometrists per capita. Lee et al1 maintain that “this method of analysis grossly underestimates availability.” This letter argues that Lee et al1 did not support these assertions and notes that it has not been established that driving time to the closest eye care provider, the measure of provider availability used by Lee et al,1 is a better predictor of vision health outcomes than other measures of the availability of eye care providers. To the first point, Lee et al1 did not present findings about the number of geographic areas with a combination of “lower” ophthalmologist availability and “higher” optometrist availability or the percentage of the population that lived in these types of areas; therefore, it is not possible to directly compare their findings with those of Gibson.2 Additionally, Lee et al1 presented no empirical evidence to support the statement that provider density measures grossly underestimate availability. Their critique that county-level provider density measures do not consider the proximity of ophthalmologists and optometrists in neighboring counties is well-taken and is also mentioned as a caveat by Gibson,2 but the validity of this point does not necessarily mean that countylevel provider density measures grossly underestimate availability. Lee et al1 estimated that >90% of US Medicare beneficiaries lived within a 30-minute drive of an ophthalmologist and within a 15-minute drive of an optometrist. Driving time may be misestimated for some residents of rural areas, because census block groups can be very large in rural areas and the estimates of Lee et al1 are based on the distance from the geographic center of an individual’s census block group of residence rather than on the distance from the precise location of an individual’s residence. Drawing on 2010 decennial census data to provide examples of the frequency and geographic distribution of large census block groups, 97 of 413 block groups in Wyoming, 941 of 15 814 block groups in Texas, and 310 of 4489 block groups in Wisconsin were >50 square miles. Based on 2010 decennial census data, 22.4% of the US population aged 65 years lived in a rural area. The number of providers per capita in a geographic area can be thought of as a rough measure of both provider proximity and provider capacity. Driving time to the closest eye care provider does not capture the capacity of providers to take on additional patients or to see existing patients in a timely fashion. Lee et al could use their data to create a measure of eye care provider capacity by calculating for each US Medicare beneficiary how many other TO THE EDITOR:
Medicare beneficiaries had the same closest provider. They could examine how this measure varied for residents of different regions of the country and for residents of rural and urban areas, and they could examine the extent to which the driving time and provider capacity measures offered consistent views on the degree of eye care provider availability. Previous research in the United States has found that measures of eye care providers per capita were significantly associated with vision health outcomes in empirical models that included a large set of controls for individual and contextual characteristics, providing evidence on the predictive validity of provider density as a measure of the availability of eye care providers.3e5 Although it stands to reason that driving time measures of eye care provider availability would be similarly associated with vision health outcomes, to my knowledge this association has yet to be examined. Until the superior predictive validity of driving times has been established, the question of which measure is the best measure of the availability of eye care providers remains unsettled.
DIANE GIBSON, PHD Marxe School of Public and International Affairs, Baruch College, City University of New York, New York, New York
Financial Disclosures: The author has no proprietary or commercial interest in any materials discussed in this article. Available online: May 22, 2017. Correspondence: Diane Gibson, PhD, Marxe School of Public and International Affairs, Baruch College - CUNY, 17 Lexington Avenue, Box D-901, New York, NY 10010. E-mail: [email protected].
References 1. Lee CS, Morris A, Van Gelder RN, Lee AY. Evaluating access to eye care in the contiguous United States by calculated driving time in the United States Medicare population. Ophthalmology. 2016;123:2456-2461. 2. Gibson D. The geographic distribution of eye care providers in the United States: implications for a national strategy to improve vision health. Prev Med. 2015;73:30-36. 3. Chou C, Zhang K, Crews J, et al. Impact of geographic density of eye care professionals on eye care among adults with diabetes. Ophthalmic Epidemiol. 2012;19:340-349. 4. Gibson D. Eye care availability and access among individuals with diabetes, diabetic retinopathy, or age-related macular degeneration. JAMA Ophthalmol. 2014;132:471-477. 5. Gibson D. The local availability of eye care providers and the vision health of adults in the United States. Ophthalmic Epidemiol. 2016;23(4):223-231. We sincerely thank Dr Gibson for her comments on our recent article concerning access to eye care providers.1 Dr Gibson notes that we have used a novel metricdshortest driving distancedas a proxy for access to care, and that comparisons of this metric with existing methodologies, such as county-level provider data studied by her own group, are difficult. We concur with this assessment, but wish to highlight ways in which we feel the current metric may differ from county-level provider data. REPLY:
e65