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Height of Tumbling E for Visual Acuity Assessments at various distances

person holding eyeglasses

When developing mobile apps / charts for assessing visual acuities using Snellen's / LogMAR notation, there is a need to estimate the size of letters for a given working distance for assessing a specific cutoff. Under normal vision, for a visual acuity of 6/6, the whole letter subtends an angle

Nginx Log Full URL in Reverse Proxy

If you run a NGINX reverse proxy hosting multiple services, you may need to see which access was for which service. The Access log can be modified to log the full URL as under

Sample size for Paired T test

Simple pre-post designs where the outcome assessed is continuous. Using pwrss package Output References

Resoucres for working with OCT images

Meta / reviews of datasets Datasets Tools Codes

Precision based Sample Size Calculation using precise in R

https://joss.theoj.org/papers/10.21105/joss.03118 https://ctu-bern.github.io/presize/ Verbatim From the article - There are two approaches for each measure. Proportion Shiny Webapp

Recommended Precision for Sample Size of Prevalence

Often people are confused about the precision that should be used when estimating sample size for prevalence studies. Some guidance here From: Sample size calculation for prevalence studies using Scalex and ScalaR calculators Expected PrevalenceRecommended PrecisionLarge ScaleSmall ScalePreliminary StudyRemark110 to 90%2 ~ 3%4 ~ 5% > 5% 2 < 10%0.25*EP0.50*EP > 0.50*EPCannot be equal to EP or larger e.g. 4%1%2% > 2%Cannot be 4% or

Sample size for Prevalence in R using epiR

Simple Random Sampling Expected prevalence 50%, relative error 10%, Finite population correction - None Expected prevalence 50%, absolute error 10%, Finite population correction - None One Stage Cluster Sampling Estimate number of clusters when Expected prevalence = 50% , relative error 10%, cluster size 75, ICC 0.2, 95% Confidence. Entire

Sample Size for Correlations

To assess sample size for an expected Pearsons correlation ρ0 between two continuous variables n = ([z1 - α + z1 − β]2/z02) + 3 Where z0 = 0.5 (ln [1 + ρ0] − ln [1 − ρ0]) This tests the hypothesis, H0: ρ = 0 versus H1: ρ = ρ0 > 0 Estimation

Logitech MX keys in Win/Mac dual OS setup

I recently started using the Logitech MX Keys and MX 2 mouse multi-device feature. Device 1 is Windows and device 2 is Mac OS. The biggest problem was the behaviour of ~ key and home/edn keys. Searching online gave me a solution Swapping PC and Mac layouts FN+O — swaps PC

February 27, 2025

Evolution of Definitions of Visual Impairments

In recent months one thought has been occurring to be regarding classification of Visual Impairment and blindness. ddd ddd I find it is strange that the most widely understood classification of blindness and visual impairment in surveys do not have complete grounding in ICD-10/ ICD-11. As you will see below,

December 25, 2024