ORIGINAL ARTICLE

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COMPARISON BETWEEN THE PANOPTIC OPHTHALMOSCOPE AND THE CONVENTIONAL DIRECT OPHTHALMOSCOPE IN THE DETECTION OF SIGHT THREATENING DIABETIC RETINOPATHY: THE KUCHING DIABETIC EYE STUDY

AK Tan^1,2,3 MD, PS Mallika³ MS, S Aziz² MS, T Asokumaran² MMed, G Intan2 MS, HA Faridah1 MS
¹Department of Ophthalmology, Pusat Perubatan Universiti Kebangsaan Malaysia (Tan Aik Kah, Faridah Hanom Annuar)
²Department of Ophthalmology, Hospital Umum Sarawak, Sarawak, Malaysia (Tan Aik Kah, Mohamad Aziz Salowi, Asokumaran Thanaraj, Intan Gudom)
³Department of Ophthalmology, Faculty of Medicine and Health Science, Universiti Malaysia Sarawak (UNIMAS), Sarawak, Malaysia (Tan Aik Kah, Mallika Premsenthil)

Address for correspondence: Dr Tan Aik Kah, Trainee Lecturer, Ophthalmology Unit, Faculty of Medicine and Health Sciences, Universiti Malaysia Sarawak, Lot 77, Sekysen 22 Kuching Town Land District, Jalan Tun Ahmad Zaidi Adruce, 93150 Kuching, Sarawak, Malaysia. Tel: +6082-416 550, Fax: + 6082-422 564, Email: portwinestain@hotmail.com, aktan@fmhs.unimas.my

Conflict of interest and funding: None

This study was conducted in the Department of Ophthalmology, Hospital Umum Sarawak.

INTRODUCTION

Diabetes is one of the most prevalent chronic conditions among Malaysians. The National Eye Survey 1996 results showed that the prevalence of diabetic retinopathy (DR) among Type 1 Diabetics (T1DM) aged 40 years and above with duration of more than five years was 14.6%.¹ Asia is expected to be home to 61% of the total global projected number of people with diabetes by 2010, as it is the most populous continent and due to increased urbanization and improved life expectancy.²

DR is a major public health problem.³ Overall, between 25% and 44% of people with diabetes at any point in time, have some form of DR. The prevalence of sight threatening retinopathy (STR), from either proliferative diabetic retinopathy (PDR) or clinically significant macular oedema (CSME) varies principally by the known duration of diabetes, with minor influences due to age and the type of diabetes.

Screening of diabetic eye disease has been proven to prevent loss of sight. In at least half of patients with PDR, severe visual loss can be prevented by Pan Retinal Photocoagulation (PRP).⁴ 50-60% of patients with visual impairment due to diabetic maculopathy, will improve by laser therapy as well.^5,6 Therefore, early intervention during the course of the disease will decrease the risk of complications, thereby reducing health care cost.

The Malaysia Clinical Practice Guideline: Diabetic Retinopathy (MCPG:DR) 1996, recognized that the lack of time and skill in detecting DR by conventional direct ophthalmoscopy (CO) hampers effective screening.³ A systematic review of published reports examining the effectiveness of ophthalmoscopy in screening for STR found that the sensitivity of detecting any STR by dilated direct ophthalmoscopy alone ranged between 43% and 96% and the specificity ranged between 87% and 100%.⁷ Even in the hands of an experienced ophthalmologist, however, CO is limited by weaknesses inherent to the instrument itself.⁸ Ophthalmologists are the clinical “reference standard” in screening and assessment of DR.³ Dilated slit lamp biomicroscopy (SLM) is now the clinical reference standard method for assessing the presence and severity of DR.

Bresnick GH et al. has developed the eye watch screening criteria (EWSC), which are based on examination of two standard retinal fields.⁹ This enable screening to be done more confidently by clinicians as it is often difficult for them to visualize the peripheral retinal field with the CO.

Retinal photography is a workable option. Although the non-mydriatic fundus camera can speed up the screening process, it is not widely available at the present moment. Non-mydriatic retinal photography may be limited by reduced sensitivity for screening and detecting DR and by technical failure with ungradable photographs caused by small pupils and media opacities. Moreover, non-mydriatic fundus photography does not currently meet the National Institute for Clinical Excellence guidelines for quality assurance objectives for DR screening tests requiring sensitivity ≥80%, specificity ≥95% and technical failure rate <5%.¹⁰

The PanOptic ophthalmoscope (PO) was developed by Welch Allyn. The company claimed that PO has several advantages over CO. PO allows fundus examination through small undilated pupils. It also provides a dramatically wider, more panoramic view of the fundus. It enables a 25° field-of-view (FOV) versus the standard 5° FOV of the CO. It increases magnification by 26% over the standard CO and it provides greater working distance.¹¹

Gill JM et al. concluded in their study that using PO to screen for DR by family physicians is not sufficiently accurate to replace routine referral for all patients with diabetes.¹² In their study however, the PO was used to screen for DR in undilated eyes. In another study by McComiskie JE et al., the medical students rated that the PO was much easier to use compared to the CO although the accuracy was similar for the two instruments.¹³

To an ophthalmologist, the advantages in terms of wider FOV and higher magnification provided by the PO is comparable to those provided by a MaxField ® STD 90D over a conventional 90D condensing lens. This potential is further enhanced by pupil dilatation. Therefore, it is timely for us to explore the full potential and limitations of the PO from the ophthalmologists’ point of view. The result of this study would provide evidence-based data on the true performance of the PO. This may provide another cost-economical option for the screening of DR in the next edition of MCPG:DR.

METHODS

This study was approved by the Malaysian Medical Research Ethic Committee (NMRR-08-1220-2539) and the Research Ethics Committee, Universiti Kebangsaan Malaysia (FF-084-2010). This was an ophthalmology clinic-based, double-masked, cross-sectional observational study. All new referrals of diabetic patients to the ophthalmology clinic of Sarawak General Hospital from 1st January 2009 to 31st May 2009 were invited to join the study. Written informed consent was obtained from all participants with due regard to the Declaration of Helsinki and Malaysian Guidelines for Good Clinical Practice (GCP).

Inclusion criteria were age 20 and above, definite diagnosis of DM (T1DM or T2DM), availability of companion to accompany patient home and willingness to give a signed written informed consent.

Exclusion criteria were patients found not suitable for pupil dilatation due to medical reasons (shallow anterior chamber angle) or social reasons, pupil dilatation less than 7 mm, history of prior laser therapy (PRP, focal or grid laser photocoagulation) or posterior segment surgery (vitrectomy) and presence of significant media opacity.

PROCEDURE

Both the PO and CO are operator dependent and patient dependent. Gill et al. showed that there is a wide range of kappa statistic, between 0.06 to 0.70, among family physicians in the screening for DR.¹² In order to avoid inter-observer and intra-observer variation, only one investigator (TAK) was assigned to perform the examinations. A nurse would inform the investigator if there was a new referral of diabetic patient. The patient’s age was determined. The patient would be asked three questions. The first question was to determine if he or she agrees to be subjected to dilated fundus examination. The second question was to determine if he or she has any companion to accompany him or her home after the examination. The third question was to determine if he or she had any prior intra-ocular surgery, including laser surgery. Next, the patient’s anterior chamber depth would be assessed with a pen torch. This is to screen for patients at risk of acute angle closure attack following pupil dilatation.

The patient would be invited to participate in this study if he or she agreed for dilated fundus examination, had companion to accompany him or her home, had no prior intra-ocular surgery and not at risk of developing acute angle closure attack. A signed written informed consent would be obtained from the patient. In order to maintain masking, there will be no further history taking at this point.

Both eyes were dilated with topical tropicamide 1.0% and phenylephrine 2.5%. After ten minutes, the pupils were examined to determine if dilatation is adequate. If pupil dilatation was inadequate (less than 7 mm), topical tropicamide 1.0% and phenylephrine 2.5% would be instilled for the second time. The eyes were re-examined after another ten minutes, if pupil dilatation was still inadequate in both eyes, the patient would be excluded from the study.

Since DM is a systemic disease, both eyes are equally affected in most patients. The knowledge of the DR status in one eye will influence the examiner’s judgment of the DR status for the contra-lateral eye. Therefore, only one eye from a particular patient would be included in this study. The investigator would perform a Bruckner test using the CO to examine the red reflex of both eyes simultaneously. The eye with the least media opacity would be included in the study. If the red reflex was equal in both eyes, the right eye would be chosen.

Coin flipping was used to determine which instrument would be used first to examine the patient; “head” for PO and “tail” for CO. As the examinations were carried out by only one investigator, the knowledge of the DR status obtained by using the first instrument will inevitably influence the judgment of the DR status obtained by using the second instrument. This constitutes a limitation of the study.

The examination would first be performed using either the PO (head) or the CO (tail), then followed by CO and PO respectively, and lastly using the SLM. After the first examination, the patient would be asked to wait for one hour while the investigator attended to other patients in the busy ophthalmology clinic. This was done with the hope that the investigator will have a vague or no memory of the fundoscopic findings with the first instrument. The second examination was performed after at least an hour. There was no history taking during the first two examinations.

A thorough history would be taken before the patient was subjected to third examination using the SLM (reference standard). The patient’s diabetic record would also be revealed. Both eyes would be examined using the SLM. Under the SLM, the investigator would be able to determine the true DR status of each eye. Hence, the investigator was unmasked. The patient would then be informed of his or her DR status as well and manage accordingly. All relevant findings were documented in the Case Report Form (CRF).

There were only three instruments involved: one CO, one PO and one slit lamp used in the study.

Pupil dilatation

We believe that DR grading without pupil dilatation is unacceptable; even in the busy primary health care setting. Pupil dilatation (using 0.5% to 1.0% tropicamide and/or 2.5% phenylephrine) is safe and markedly increases the sensitivity of DR screening. The Melbourne Visual Impairment Project (MVIP) and Blue Mountain Eye Study (BMES) showed high levels of patient acceptance for pupil dilatation. These studies have also confirmed the safety of pupil dilatation. The examiner will screen the patients prior to pupil dilatation as mentioned above.

Conventional direct ophthalmoscopy (CO): Welch-Allyn model 11740

Conventional direct ophthalmoscopy was performed after pupil dilatation in a dark room. For the detection and grading of DR and DME, the examiner will first examine the optic disc, then the superior nasal quadrant, superior temporal quadrant, inferior nasal quadrant, inferior temporal quadrant and lastly the macula. Examinations were also done using the red-free light.

PanOptic Ophthalmoscope (PO): Welch-Allyn model 11820

PanOptic ophthalmoscopy was performed after pupil dilatation in a dark room. The side cup provided by the manufacturer was not used. For the detection and grading of DR and DME, the examiner will first examine the optic disc, then the superior nasal quadrant, superior temporal quadrant, inferior nasal quadrant, inferior temporal quadrant and lastly the macula. Examinations were also done using the red-free light. The investigator was given a PO for three months for him to familiarize himself with the equipment.

Slit Lamp Biomicroscopy (SLM): Inami model L-0240

Slit lamp biomicroscopy was performed using the MaxField®STD 90D and Volk Double Aspheric 78D condensing lens. Examinations were also done using the red-free light.

DEFINITION OF TERMS

The Early Treatment Diabetic Retinopathy Study (ETDRS) staging system is the reference standard for grading in clinical trials and epidemiologic studies. However, its use in daily clinical practice is limited by relatively complicated rules, multiple severity levels and need to correlate with standard photographs. In September 2001, the American Academy of Ophthalmology (AAO) launched the Global Diabetic Retinopathy Project to promote the development of a common clinical severity scale for DR and diabetic macular oedema (DME), to facilitate improved communication between retina sub-specialists, ophthalmologists, endocrinologists/diabetologists and primary care physicians. 

The International Clinical Diabetic Retinopathy and Diabetic Macula Edema Disease (ICDR and DMED) Severity Scale proposed five severity levels of DR - none, mild, moderate, severe and proliferative; in the presence or absence of macular oedema, which is graded separately.^14,15 (The International Clinical Diabetic Retinopathy Disease Severity Scale is available at http://www.icoph.org/pdf/Diabetic-Retinopathy-Scale.pdf. The International Clinical Diabetic Macular Edema Disease Severity Scale is available at http://www.icoph.org/pdf/Macular-Edema-Scale.pdf ). In this proposed new scale, the examiner might evaluate the individual lesions, but will record only the overall severity level. This clinical severity scale has been adopted by the Prevention of Blindness Committee, Ministry of Health, Malaysia, to facilitate screening and referral of DR cases among the primary health care workers.

Sight Threatening Retinopathy (STR) is defined by the presence of either:^16,17
i.   Severe NPDR or worse;
ii.  Moderate DME or worse

“Ease of use” grading for CO and PO

The “Ease of use” grading for both CO and PO was adopted from the work of McComiskie et al.:¹³

1. Could not use this scope
2. Could not see the red reflex to even begin
3. Could not focus the fundus
4. Could see vessels but not the disc
5. Could see disc and retinal fields but it wasn't in focus
6. Determined clinical severity with high level of difficulty
7. Determined clinical severity with medium level of difficulty
8. Determined clinical severity with low level of difficulty
9. Determined clinical severity very easily