Abashyna N.M.; Kuryltsiv N.B.

Lviv state medical university.

Heidelberg Retinal Tomography in early diagnosis

of primary glaucoma

Treatment for any disease begins with an accurate diagnosis. For glaucoma, this means not merely looking for changes of intraocular pressure and in the visual field but examining changes of the optic nerve. Structural damage can occur without functional loss, so early detection allows treatment to begin sooner. For early diagnosis of primary glaucoma (PG) we can use Heidelberg Retinal Tomography (HRT). It allows examine the optic disc and retinal nerve fiber layer accurately.

 We conducted our research in Chicago Eye Institute from June to September 2006. 208 patients (included 146 woman), aged 41 to 89, with glaucoma suspected were examined there. For effective diagnostics of PG we used a set of five evaluation rules of the HRT results (Felipe A. Medeiros, MD):

Rule 1. Observe the scleral ring.

Clinicians must identify the scleral ring to evalu­ate the limits and size of the optic disc. The scleral ring is a white band encircling the optic nerve. It is more clearly visible in the temporal region. Once identified, the optic nerve can be delimitated and vertical and horizontal diameters identified. A direct oph­thalmoscope or slit-lamp biomicroscopy with a high-diopter lens can be used to evaluate optic disc size. Optic disc size can be classified as small, average or large. Average vertical diameter is 1.8 mm. Large – greater than 2.2 mm, small discs – 1.5 mm or less. Measuring the optic disc size is important as size of the optic disc cup varies with the size of the disc. Therefore, large optic discs in healthy individuals tend to have large cups, which can lead to an erroneous diagnosis of glaucoma. On the other hand, small cups can be glaucomatous in patients with small discs.

Rule 2: Identify size of neuroretinal rim.

The width of the neuroretinal rim must be evaluat­ed in all sectors of the optic disc. The width of the rim is the distance between the border of the disc and position of blood vessel bending. To correct­ly evaluate the position of blood vessel bending, clin­icians must have a stereoscopic view of the optic disc, with the help of stereoscopic optic disc photographs or slit lamp examination.

A healthy disc follows the ISNT rule: the inferior rim is thicker than the superior rim, which is thicker than the nasal rim, which is thicker than the temporal rim. When the rim configuration does not obey the ISNT rule, glaucomatous damage must be suspected. The color of the rim is also important. Pallor of the rim increases the likelihood that a non-glaucomatous optic neuropathy is present, especially when pallor is greater than cup size.

Rule 3: Examine Retinal nerve fiber layer (RNFL).

 RNFL examination should be performed using red-free RNFL photographs or the green light at the slit lamp.

Eye care professionals should look at three char­acteristics of the RNFL: the presence of brightness and striation and the visibility of parapapillary retinal vessels. They should search for diffuse and localized retinal nerve fiber layer loss. RNFL loss in glaucoma can occur in a diffuse, localized or mixed pattern. With diffuse loss, there is diffuse reduction of the RNFL brightness and striations. Localized RNFL loss appears as wedge-shaped dark areas emanating from the optic disc. As nerve fibers become lost, the borders of the parapapillary retinal vessels are more easily visible.

Rule 4: Examine parapapillary atrophy.

Clinicians must examine the region of parapapil­lary atrophy, which can be divided into two zones. The alpha zone is represented by hypo-and hyperpigmented areas. Therefore, the presence of an alpha zone is generally not helpful in determining if a disc is glaucomatous.

The second area is the beta zone. It is an area of atrophy of the retinal pigment epithelium. It appears as a whitish area around the optic nerve that should not be confused with the scleral ring.

If both alpha and beta zones are present, the alpha zone is always peripheral to the beta zone.

The beta zone is more common in glaucomatous eyes than in healthy eyes. More importantly, the size of the parapapillary atrophy zone correlates with the area of neuroretinal rim loss. The thinner the rim, the larger the area of parapapillary atrophy. Therefore, if a zone of parapapillary atrophy is detected, clinicians should look to the corresponding area of the rim.

Rule 5: Look for retinal and optic disc hemorrhages.

Finally, the clinicians are looking for on the pres­ence of retinal and optic disc hemorrhages. Optic disc hemorrhages are indicative of glaucoma progression and appear as flame-shaped hemor­rhages. These normally disappear after 2 to 6 months. They are commonly followed by progressive rim thinning in the corresponding area, progressive retinal nerve fiber loss or broadening of a preexisting RNFL defect.

Detection of disc hemorrhage requires careful optic disc examination, as the hemorrhages can be small and easily missed.

         The obtained result of our research are: primary glaucoma is diagnosed in 92% patients, included mild in 77% person, moderate – 13,2%, severe greater – 0,8% patients. Secondary glaucoma is diagnosed in 3,3 % patients, normal-tension glaucoma – 4,7%. It took nearly 16,5 minutes to test the both patient’s eyes. The advantage of HRT for early diagnosis of PG is the absence of necessity at hospitalization and using any drug. This test does not have any side effects. As a result, there are no patient complaints.

         Our experience of using HRT leads us to the confidence, that retinal tomography is very effective, easy-to-use and precision test for early diagnosis of primary glaucoma. It is expediently to inculcate this diagnostic method to the ophthalmological practice.