IOP by Goldman Applanation Tonometry and the Tono-Pen in Afro-Americans

ABSTRACT

One hundred subjects attending the Preventative-Community Opthalmology Service in a community-based primary care center (Southside Healthcare, SW Atlanta, GA) were examined between January 24, 1996 and April 26, 1996. Ninety-nine African Americans and one Hispanic subject contributed 113 patient visits, hence there were 226 eye pairs for analysis. The mean age (n=100) was 55.8ñ16.8 years (x+sd). There were 62 females (54.2ñ17.8 years) and 38 males (58.3ñ14.9 years). The Kowa (portable) applanation tonometer and Tono-Pen (Mentor) were employed to measure the intraocular pressure in subjects at high risk for severe visual loss from either hypertension (glaucoma), diabetes (retinopathy), or HIV-related ocular syndromes. Assignment to order of measurement device was done randomly by coin-flip. The mean IOP for Kowa was 19.56ñ4.55mmHg and Tono-Pen was 19.53ñ4.63mmHg. Data from scatter plot with regression line indicate that an increase of 1mmHg for Kowa applanation tonometer was associated with 0.73mmHg for the Tono-Pen; hence the correlation factor r=0.58. Both tonometers are virtually comparable at 16-24mmHg range. The Tono-Pen demonstrated significant error at both the high (IOP>25mmHg) and low (IOP<12mmHg) ranges. Our data indicate that for low IOP range (10-15mmHg) the Tono-Pen read 2.6mmHg higher than the Kowa tonometer; similarly within the high IOP range (>25mmHg) the Tono-Pen read 4.2mmHg lower than the Applanation tonometer. The clinical caveats to primary care doctors screening emergency room patients are to ensure that ocular hypotony, a pertinent physical finding in penetrating eye injuries, is not overlooked with Tono-Pen tonometry. Studies comparing Goldman slit lamp mounted Applanation tonometers and Tono-Pen devices indicate that consistencies exist at both the high (>24) and low (<12) IOP ranges. (AU)