The Tonopen XL Tonometer and Observers

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1 {:]i~ wtu~,t Taiwan Vet J 35 (I): 15-20,2009 The Tonopen XL Tonometer and Observers 1,2 Shiun-Long LIN, 1,2 Feng-Pang CHENG, 2Yung-Chang LIN and *1Way-Shyan WAN G 1 Veterinary Medical Teaching Hospital, College of Veterinary Ntedicine, National Chung-Hsing University, Taichung, 402 Taiwan 2 Department of Veterinary Medicine, College of Veterinary Medicine, National Chung-Hsing Universit y, Taichung, 402 Taiwan (Received: August 20, Accepted: November 20, 2008 ) ABSTRACT The Tonope n XL app lanat ion tonometer has become a popu lar inst rume nt for estimat ing lo P because of its use for acquisition of clinically reliable read ings in many species. Afte r five years us ing of t he Tonope n XL, we observed the unstable resu lts from clinical practice. We presume t hat different users might give rise to different readings upon Tonopen XL applantation. Thirty-eight Beag les were tested by three individual veterinarians with various experiences. Veterinarian A experienced with Tonopen XL for over 4 years, Veteri narian B two years, and Vete rinarian C experienced on ly several days. Each Veterinarian measured t he lop of each dog respectively and the readi ngs were reco rded w hile Tonopen XL@'s error rate was 5%. No s ignificant difference was de tected be tween Veterinarian A and B, How eve r, sign ificant differe nces exist between Veterinarian C and both A and B. This res ult indicates that intra-oc ular pressure measu rement, app lied by Tonope n XL manipulation, could be largely affe cted by the skillfulness of the user. Thus proper usag e of Tonopen XL requires sufficient training and knowledge of all users. [Lin SL, Cheng FP, Lin YC, *Wang WS. The Tonopen XL and observers. Taiw an Vet J 35 (1) : 15-20,2009. " Corresponding author TEL: (04) ~36 9, FAX: (04) , wswang@dragon.nchu.edu.tw] Key word: intraocular pressure, lop, tonopen XL, tonometry INTRODUCTION Glaucoma has been one of the most important diseas e in Ophthalmology. When the intraocular pres sure (lop) increases, a human patient will suffer from headache, nausea, uncomfortable, and decrease vision [8]. However, the owner doesn't usually notice the increasing lop ofhis pet until the animal shows severe clinical symptoms, such as marked depression, blepharospasm, epiphora, corneal oedema, and episcl eral congestion [17]. At this point, it is almost too late to treat the animal. Mo re over, the lop exceeding 50 mmhg could trigger blindness. Thus, tonometry now has become an ess ential diagnostic procedure during eye examinations in animals [18]. Intraocular pressure (lop) measurement has an important role in the diagnosis of ocular dis eas es and monito ring of glaucoma in dogs. Tonometry is a indirect measurement of lop [9]. There are many kinds of tonometers clinically widely used, the Mackay-Marg, Tonopen XL, and pn eumatonograph tonometer, but the Tonopen XL is the mo st used by clinical veterinarians be-

2 16 Shiun -Long LIN et al cause of its small size, high reliability, and affordable cost [18]. The Veter inary Teaching Hospital of Chung Hsing University in Taiwan has brought Tono- pen 8 year s ago. We notice instable result s of measurements among var ious veteri narians, despi te the fact that ever y one ofus has greatly studied the instructio n and follow the proce dures comp letely. The Tonope n XL can display the average value of meas urements and its error rate (5%, 10%, 15%, and 20%) at the same time. There were seve ral reports describing the lop values obtained using different tonometer and the side effect oftonopen XL. The purpose ofthis study is to compare lop measured in vivo by Tonopen XL in clinically normal dogs, under three differe nt observers and to asce rtain the readings validity. MATERIALS AND METHODS Seve nty-six clinically normal eyes in thirty eight healthy Beag les, aged from 5-6 months, and weighted kg, 2 1 males and 17 females, complete slit-lamp biomicroscopic examination (Kowa SL- 14, Kowa Company, Tokyo, Japan) were perfo rmed on both eyes of each dog. Each dog was restrained by an assistant in normal position and topical anesthetic Proparacaine Hydrochloride (0.5% Alca ine", Alcon) was given on each cornea right 1 minu te before the Tonope n XL applanat ion for lo P readi ng. The dog was restrained properly, taking care to avo id putting pressure against the globe or the jugular vein. Three veteri narians measurement with the Tonope n XL was performed 2 min apar t from the other one. Among the three veterinarians, Veterinarian A has used Tono-Pen for more than four years, Veterinarian B two years, and Veterinarian C only a coup le of days. Each one of them performed the examination procedure exactly following Tono-Pen Manual. Each observer measured the lop several times in each dog respectively until the lop error rate was in 5% and recorded it. We perform the statis tical analysis by SAS ANOVA and Duncan grouping on the resu lts from all three Veterinarians. RESULTS The lop was measured by three differe nt veterinarians with Tonopen XL in 38 norma l beagles and the distribution of whole data was show in Fig. 1. With readings obtained from Veterinarian A, the mean ± SD lop was ± mmhg, and ranged from 9 to 28 mmhg; from Veterinarian B the mean lop was ± 3.36 mmhg, and ranged from 8 to 29mmHg; from Veterinarian C, the mean lop was ± 5.70 mmhg, and ranged was from 9 to 43 mmhg (Fig. 2 and Table I). The distribution of lop in these 38 dogs from three veterinarians detected by Tonopen XL was shown in Fig. I. From the results of statistical analysis, throug h SAS ANOVA and Duncan Grouping treatm ent, we found an extre mely significa nt differ- Fig. 1 Results of the lop read ing with Tonopen XL by three different veter inarians (Vet A, Vet B and Vet C) in 38 Beag les

3 The Tonopen XL and User 17 Table 1. Mean and standard deviation of the lop reading with Tonopen XL by 3 different veterinarians in 38 Beagle dogs. Veterinar ian A B C bil 22 ::r: 20 '-' 0.. Q I I VetA Vet B Vet C Observers Fig. 2 Mean and standard deviation of the lop reading with Tono-Pen by different veterinarian in 38 Beagle dogs. Showed extremely significant differences between Veterinarian C and the other two. The lop (mea n ± SO) ± 3.15 " ± 3.36 " ± 5.70 b Different alpha betical characters indicate significa nt difference betwee n gro ups (P<O.OO 1). ence between Veterinarian C and the other two veterinarians respectively, yet, no significa nt difference between Veterinarian A and B. DISCUSSION Th e glaucoma in the dog and cat consist of a group ofdiseases that share a common feature ofelevated intraocular pressur e (lop), retinal ganglion cell loss and optic nerve atrophy [4]. Tono metry, an indirect measur ement ofi OP via digital palpation, indentation, and applanation techniques, is an esse ntial diagn ostic procedure for almost eve ry ocular examination of animals. Owi ng to its simple and nonin vasive characteristics, tonometry allows the exa miner to evaluate intraocular hyp erten sion or hypotension and to intermittently monit or glaucomatous eyes for progress ion or resp onse to therapy. The Tonopen XL applanation tonometer has become a popular instrument for estimating lop because of its use for acquisition of clinically reliable readings in many species [9]. The Tonopen XL is a miniaturized Mackay-Marg tonometer with electronic signal analysis and digital pressure display [6]. Because of its portability, reliability, and relatively low cost, Tonop en XL has become the most popul ar instrument amo ng veter inary ophthalmolo-,a. gists for measur ement of lop in different animal includ ing rat [5,12]. There are a grea t numb er ofstudi es to compare the intraocular pressur e values obtained using Tonop en XL and other tonometers in dogs, human and the other animals. Throughout the entire research in general, the readings oflop by TonoP en has no significant difference with other tonometers [5-7,10,14,15]. In the clinical setting, the Tonopen XL had given a more eas ily interp reted digital readout than the MacKay-Marg. The sma ller sensitive tip also permitted preci se application to the cornea, which may be usefu l in some patients with diseased corneas [10]. But there is a disput ation about the incorrect high lop values in human eyes with a thick cornea using applanation tonometry [2,3,8, 11,16]. By the way, some doctors describe signs and symptoms of latex allergy associated with the use of the TonoP en in a patient with severe latex allergy. Tonopen XL covers, contained latex, induc ed agitation, bilateral conj unctival injection, eyelid erythema, and eyelid edema in latexallergic patient [1]. Maybe this is why most of ophthalm ologic doctors measure the lop ofhuman pati ent will choose that un-cont acted pneumatonograph tonometer. For Tono-Pen tonometry, topical anesthetic is instilled, and the eye lids are retracted. The prob e tip is gently and repeatedly used to contact the central cornea [18]. In the past ten yea rs applanation of this instru ment, we observe the instable results of measurements from the clini cal cases. For it is possible to get different results by applying different pressures on cornea through Tonopen XL. We presum e that different users might give rise to different result s. Previous reports indicated that lop varies with age [13]. The first part of this experim ent is to test on the same age 38 Beagle s performed by three different veterinarians using Tonop en XL at the same time. Among the three veterinarians, Veterin arian A has used Tonop en XL

4 18 Shiun-Long LIN et al for more than four years, Veterinarian B two years and Veterinarian C a couple of days. Each Veterinarian measuredthe lop of each dog respectively and the readings were recorded while Tonopen XL@'s error rate is in 5%. The reported normal range in the dog is approximately 16.7 ± 4.0 mmhg [13]. From this research the lop detected by Veterinarian A, and B is 16.67± 3. I5 mmhg, ± 3.36 mmhg. But Veterinarian C is ± 3.36 mmhg quite different from normal range as reported. There are no significant differences between Veterinarian A and Veterinarian B, however, it showed extremely significant differences betweenveterinarian C and the other two and the stander deviation of these 3 veterinarians is C (± 5.70) > B (± 3.36) > A (± 3.I5) (Fig. 2 and Table I). This result indicates that checking intra-ocular pressure by Tonopen XL@, although easily-operat ed, could get easily affected by the experiences of the clinical veterinarians. The M retractor bulbi in dogs' eyes will retract the eye backwards when the cornea contacts with the probe of Tonopen XL@and affect the value of measurement. It is suggested for a veterinarian to apply anesthesia on cornea before performing the measurement by Tonopen XL@and keep the touch ofprobe and cornea at a right angle. Besides, remember to avoid measurements on ulcer lesions and scars. It is a good design that TonopenXL itself can record, display and memorizethe result along with the error rate, so that a user may reduce the artificial error as much as possible. The result of this experiment shows that an inexperienced user such as Veterinarian C could get significantly different readings from Veterinarian A and B. Yet, there is no significant difference between Veterinarian A and B. The unpredictable result of an inexperienced veterinarian may result from the unstable pressure applied on cornea through Tonopen XL@. The error is beyond the compensation power of design of TonopenXL@. The error of this value might be greatly diverse if the users apply different strength in multiple applications on each cornea using Tonopen XL@. For this reason, we suppose that checking lop by Tonopen XL@, although easily-operated, could get easily affected by the experiences of the clinical veterinarians. That's why there is a new production the rebound tonometer ICare@in 200 I. But as well the easily using the Tonopen XL is still the most popular tonometer for veterinarian and pediatric ophthalmolog ist. Thus proper usage of Tonopen XL requires sufficient training and knowledge (of user instruction) of all users. REF ERENCES 1. Bergwerl< I<L. I<odsi SR. Latex allergy associated with the lat ex cover on the TonoPen. Am J Ophtha lmol 127: Dohadwala AA. Munger R. Damji I<F. Positive correlation between Tono-Pen intraocu lar pre ssure and central corneal thi ckne ss. Ophthalmology 105: Feltgen N. Feif ert D. Funl< J. Correlation between cent ral corneal thickness, app lanation tonometry, and direct int racameral lop readings. Bri J Ophthalmol 85: 85-87, Gelatt I<N, Gelatt JP. Surgica l procedures for treatment of the glaucoma. In: Gelatt I<N, Gelatt JP. Pergamon Handbook of Small Animal Ophthalmic Surge ry Vol 2: Cornea l and Intraocular Procedures. Pergamon, , Gelatt I<N, Macl<ay EO. Distribution of int raocular pre ssure in dogs. Vet Ophthalmol 1: , Hessemer V, Rossler R.. j acobi I<W. Tone -Pen, a new tonometer. Int Ophthalmol 13: 51-56, lest er M, Mermoud A. Achache F. Roy S. New Tonopen XL: Comparison with the Goldmann tonometer. Eye 15: I<ansl<i JJ. The Glaucoma s-methods of examination. In: I<ansl<i JJ. Clinical Ophthalmo logy, Heinemann, '0 ed. Butterworth 9. Leiva M, Naranjo C, Peria MT. Compar ison of the rebound tonometer (ICare" ) to the applanation tonometer (Tonopen XL" ) in normotensive dogs. Vet Ophthalmol 9 (1) : Miller PE, Phillip PJ. Majors LJ, I<urzman 10. Evaluat ion of two applanation tonometers in cats. Am J Vet Res 52: , Mol< I<H. Wong CS, Lee VW. Tono-Pen tonometer and corneal thlckness. Eye 13: Moore CG.. Milne ST, Morrison JC. Noninva sive measurement of rat int raocular pre ssure with the Tono- Pen. Inv Ophthal Visua l Sci 34 : , Mughannam AJ. cook CS, Fritz CL. Change in intraocuiar pre ssure during maturation in Labrador Ret riever dogs. Vet Ophtha l (2): 87-89, Paranhos AJ. Paranhos FR. Prata JJ, Omi CA. Mello PA. Shields MB. Infiuence of I<eratometric readings on comparative intraocular pressure measurements with Goldmann, Tone- Pen, and noncontact tonometers. J Glaucoma 9 : Priehs DR. Gum GG., David WR, Moore LE. Evaluat ion of three applanation tonometers in dogs. Am J Vet Res 51: , 1990.

5 The Tonopen XL lij and User Rao VJ. Gnanaraj L. Mitchell I<W. Figueiredo FC. Clinical comparison of ocular blood f low tonometer. Tonopen, and Goldmann applanation tonometer for measuring intraocular pr essure in postker atoplas t y eyes. Cornea 20: Renwick PW. Glaucoma. In: Petersen-Jones SM. Cr ispin S. Manual of Small Anima l Ophthalmology. Sri Sm Anil Vet Associ Strubbe. Gelatt. Ophthalmic examination and diagno stic procedure s. In: Gelatt I<N. Veterinary Ophth almology 3,d ed. Lippin cott Williams & Wilkin s

6 20 Shiun-Long LIN et at 眼壓筆檢查與使用者的關係 1,2 林茍龍 1,2 鄭豐邦 2 林永昌叫玉清賢 1 國立中興大學獸醫教學醫院台中市 2 國立中興大學獸醫學系台中市 ( 收稿日期 : 97 年 8 月 27 日 接受日期 : 97 年 11 月 20 日 ) ; 自要眼壓計是用來檢查眼球壓力, 以監測青光眼的程度及治療的反應 眼壓筆 (To n o P e n ) 以其輕巧攜帶容易 可信度高及價格適中, 已經是獸醫師最流行用來檢測各種動物眼壓的工具 國立中興大學獸醫教學醫院經多年臨床使用發現其測量值差異頗大, 可能隨著眼壓筆探頭接觸角膜力道的不同而產生不同的結果 因此推測不同人使用眼壓筆將可能產生不同的結果 本實驗 ( 1 ) 以 3 8 隻米格魯犬 ( 5 至 6 月齡 5 至 7 回 3 公斤 2 1 隻雄性 1 7 隻雌性 ) 及三位獸醫師為對象, 其中 A 獸醫師使用眼壓筆已經 4 年多 B 獸醫師 2 年 c 獸醫師使用過數次 每一隻犬的眼球均被三位獸醫師以眼壓筆測量, 並記錄眼壓筆本身誤差為 5% 之測量值 三者之測量值經 SAS 統計軟體之變方分析及 D u n c a n grouping 處理發現 C 之測量值與 A B 有非常極顯著差異 (p < 0.001) ; 而 A 與 B 無顯著差異 顯示眼壓筆雖然操作 簡單但易有人為誤差, 臨床上仍須有經驗獸醫師操作 [ 林茍龍 鄭豐邦 林永昌 * 玉清賢 自民壓筆檢查與使用者的關條 台灣獸醫誌 3 5 (1): * 聯絡人 TEL : (04) FAX. (04) wswang@ dragon.nchu.edu.tw] 品質訝 : DB, 廬, 品穿盧計, 艘軍皇宮 XL