Systematic Error in Computerized Pachymetry

Stucchi, C.A.; Gennari, G.; Aimino, G.; Carlo, I. di; Bauchiero, L.

doi:10.1159/000310434

Cited by 9 publications

(8 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…21 Only a few studies have attempted to evaluate the variability of ultrasonic pachymetry: their results show a good degree of reproducibility, although most of them involved small sample sizes or were designed to compare ultrasonic pachymetry with other methods of measuring CCT. [22][23][24][25][26][27][28][29] The aim of this study is to evaluate the variability of ultrasonic pachymeter in the clinical setting and to provide a quantitative estimate of expected CCT measurements repeated by the same or different operators.…”

mentioning

confidence: 99%

Intraobserver and interobserver reproducibility in the evaluation of ultrasonic pachymetry measurements of central corneal thickness

Miglior

2004

British Journal of Ophthalmology

151

View full text Add to dashboard Cite

Purpose: To assess reproducibility of central corneal thickness (CCT) measurement by means of ultrasonic pachymetry. Methods: Fifty one volunteers underwent three sessions of CCT measurements, each consisting of three CCT measurements, performed by each of three different observers. Intraand interobserver reproducibility was calculated by means of intraclass correlation coefficient (ICC). The expected range of variability between two independent evaluations was calculated using scatter plots of each test-retest difference against their mean. The standard deviation of the mean differences in the test-retest scores was used to describe the differences in the score spread. Results: The ICC ranges of the intra-and interobserver evaluations were 0.95-0.97 and 0.89-0.95 respectively; the expected variability was (¡1% and (¡ 2% respectively (95% confidence interval). Conclusions: The measurement of CCT by means of ultrasonic pachymetry is highly reproducible.T he measurement of central corneal thickness (CCT) is an important step in ophthalmic evaluations preceding kerato-refractive surgery.1 It is also an increasingly important procedure in the evaluation of patients with ocular hypertension (OHT) or glaucoma. CCT can be clinically assessed by means of optical or ultrasonic pachymetry, 2 and optical coherence tomography. 21Only a few studies have attempted to evaluate the variability of ultrasonic pachymetry: their results show a good degree of reproducibility, although most of them involved small sample sizes or were designed to compare ultrasonic pachymetry with other methods of measuring CCT. 22-29The aim of this study is to evaluate the variability of ultrasonic pachymeter in the clinical setting and to provide a quantitative estimate of expected CCT measurements repeated by the same or different operators. MATERIALS AND METHODSOne eye was randomly chosen for each of 51 volunteers aged 49-82 years (31 healthy individuals, 16 patients with OHT, and four patients with primary open angle glaucoma).Individuals with previous corneal surgery, previous or current corneal disease, and contact lens wear were excluded from the study.Ultrasonic pachymetry was performed with an undilated pupil using an ''Altair'' Ultrasonic Pachymeter (Optikon 2000, Rome, Italy) whose probe tip is approximately 1 mm in diameter.The pachymeter was calibrated at the beginning of each session. After the instillation of a topical anaesthetic (oxibuprocain 0.4%), the probe was placed perpendicularly on the central cornea. This was confirmed by an audible beep produced by the instrument.Three well trained operators (EA, MG, GM) independently measured the CCT of each eye in a random sequence within 3-4 minutes of each other in order to rule out the influence of possible diurnal variations in CCT. [30][31][32][33] In order to reduce the possibility of ocular surface drying, 27 one drop of artificial tear (Dacriosol, Alcon, Fort Worth, TX, USA) was instilled 30 seconds before each measurement. Each measurement was recorded by an assistant. The observe...

show abstract

mentioning

confidence: 99%

Intraobserver and interobserver reproducibility in the evaluation of ultrasonic pachymetry measurements of central corneal thickness

Miglior

2004

British Journal of Ophthalmology

151

View full text Add to dashboard Cite

show abstract

“…All the measurements were taken late in the morning. Recently, Stucchi et al [3] have reported how the instillation of oxybuprocain 4% associated with the prone position may cause a nonnegligible alteration in the thickness of the corneal surface, but, considering that such phenomena take place, according to the same authors, this only happens at specific hours, so it cannot significantly affect our cases.…”

Section: Discussionmentioning

confidence: 76%

“…Regarding this, the literary contribution is very poor. Even if many authors have underlined the necessity of reducing corneal pain, limiting the light beam and the number of maneuvers during measurements potentially capable of altering the corneal hydration status, only a few of them have quantified the entity of that phenomenon [1,2,3].…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Eventual Error Caused by Dehydration with Pachometry

et al. 2001

View full text Add to dashboard Cite

Among the possible variables responsible for systemic errors in the acquisition of pachometric measurements, the corneal hydration condition plays a determinant role. In the present study, the authors have investigated the importance of this condition with two different pachometers (Storz Corneoscan II and Allergan Humphrey), reproducing an experimental dehydrated condition. The main datum arising from the comparison of the measurements obtained is represented by the different time course of the value of the measurement in the two groups. In fact, confronting the medium initial superimposed thickness value in the two tables (521 vs. 520 µm) there is a substantial difference in the final examination. For the first group of 60 corneas, the thickness values appear almost identical in the different intervals of time (medium initial thickness 521 vs. 512 µm final thickness). For the group examined with the solid-point machine, a decreasing thickness equal to 7% was evidenced (520 vs. 482 µm) with a significant decrease in the corneal thickness after only 45 s.

show abstract

“…One explanation for this observation lies in the fact that the left eyes had more time between instillation of anesthetic eye drops and the CCT measurement than did the right eyes, possibly leading to greater drying of the cornea on the left. Stucchi et al 29 described the role of corneal surface hydration in ultrasound pachymetry. Additionally, there might be more variability in the CCT measurement of a left eye by a right-handed examiner.…”

Section: Discussionmentioning

confidence: 99%