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ID naloge: 172 Letnik: 2003 Predmet: oftalmologija
ELEKTROFIZIOLOŠKA OCENA DELOVANJA CEPNIC PRI BOLNIKIH S PIGMENTNO RETINOPATIJO
Avtor: Tomaž Friedrich, Helena Skacej
Mentor: prof. dr. Marko Hawlina
Somentor: viš. znans. sod. dr. Jelka Brecelj
IZHODIŠCE: Skotopicna in fotopicna elektroretinografija (SF ERG) je temeljna elektrofiziološka preiskava za vrednotenje delovanja mrežnice. Poteka v skladu s standardi, ki se sproti dopolnjujejo z novimi dognanji z namenom izboljšati klinicno vrednost te preiskave. SF ERG ima pomembno vlogo v obravnavi bolnikov z najpogostejšo distrofijo mrežnice, pigmentno retinopatijo (RP). To je klinicno in genetsko zelo raznolika bolezen, za katero je znacilen napredujoc in generaliziran propad palicnic in cepnic, posledicno pa tudi ostalih celic mrežnice. V prepoznavanju in spremljanju RP se poleg SF ERG, ki je objektivna preiskava, uporabljajo tudi razlicne psihofizicne preiskave. Med temi sta najpomembnejši dolocanje vidne ostrine in vidnega polja.
NAMEN: Želeli smo izdelati normativne vrednosti za SF ERG z novim stimulatorjem, ki proizvaja dražljaje (bliske) z višjo svetilnostjo, kot so jo v našem laboratoriju uporabljali doslej. Vpliv visoke svetilnosti smo hoteli preveriti pri bolnikih z RP. Poleg tega smo za draženje cepnic, ki so v poteku bolezni najdalje ohranjene, uvedli tudi vecje število ponovitev dražljaja, kar se je razlikovalo od standardov. S tem smo poskušali objektivneje ovrednotiti delovanje cepnic pri bolnikih z RP. Pri njih smo želeli tudi ugotoviti, ali obstaja povezava med odgovori SF ERG ter izvidi vidne ostrine in vidnega polja.
HIPOTEZE: 1. Pri zdravih prostovoljcih in pri bolnikih z RP smo zaradi višje svetilnosti dražljaja pricakovali višje odgovore v primerjavi z vrednostmi, dobljenimi z dražljaji nižje svetilnosti. 2. Za bolnike z RP smo predvidevali, da bodo odgovori cepnic, draženih z vecjim številom ponovitev dražljaja, prisotni pri vec bolnikih kot pri standardnem nacinu draženja. 3. Predpostavili smo tudi, da med odgovori SF ERG ter izvidi vidne ostrine in vidnega polja obstaja povezanost.
METODE: V preiskavi je sodelovalo 30 zdravih prostovoljcev (34,8 14,7 let) in 16 bolnikov z RP (32,4 16,3 leta) obeh spolov. Vsi zdravi preiskovanci so imeli vidno ostrino 1,0 ter ocesno ozadje brez bolezenskih sprememb. Posneli smo jim odgovore SF ERG s stimulatorjem visoke svetilnosti. Kot aktivne elektrode smo uporabili HK-elektrode. Priprava preiskovancev in nastavitve parametrov SF ERG so bili, z izjemo vecjega števila ponovitev dražljaja pri snemanju odgovora cepnic, v skladu s standardi. Bolniki, ki so sodelovali v raziskavi, so imeli rod-cone obliko RP ter merljivo vidno ostrino in vidno polje. Obseg slednjega smo dolocili s kineticnim perimetrom, obcutljivost pa s staticnim perimetrom. Tudi njim smo posneli odgovore SF ERG. S testom Kolmogorov-Smirnov smo ugotavljali nacin porazdelitve dobljenih podatkov. Wilcoxonov test predznacenih rangov smo pri zdravih prostovoljcih uporabili za dolocitev razlik med rezultati, dobljenimi z višjo in z nižjo svetilnostjo dražljaja. Z istim testom smo pri bolnikih dokazovali razlike v ohranjenosti odgovorov cepnic, draženih z vecjim in manjšim številom ponovitev dražljaja. Povezave med SF ERG in vidno ostrino ter vidnim poljem smo preverjali s koeficientom korelacije po Spearmanu (r).
REZULTATI: Pri zdravih preiskovancih so bile amplitude odgovorov SF ERG, dobljene z uporabo visoke svetilnosti dražljaja, pomembno višje od vrednosti, dolocenih z dražljaji nižje svetilnosti (p = 0,008), medtem ko se latence statisticno niso razlikovale (p = 0,075). Koeficienti variacije (KV) amplitud so bili pri uporabi visoke svetilnosti dražljaja nižji (p = 0,008) kot KV amplitud, izracunanih na osnovi nižje svetilnosti dražljaja, KV latenc pa se med obema svetilnostima niso statisticno razlikovali (p = 0,767). Tudi pri bolnikih z RP so bile amplitude odgovorov SF ERG višje pri uporabi dražljajev z visoko svetilnostjo. Poleg tega smo z uporabo takšnega nacina draženja pri enem izmed dveh nakljucno izbranih bolnikov zaznali odgovor, ki je bil pri nižji svetilnosti dražljaja neizziven. Med vsemi odgovori SF ERG je bil odgovor cepnic pri draženju mrežnice z vec ponovitvami dražljaja prisoten pri najvecjem deležu oci bolnikov (68,8 %), medtem ko so bili odgovori palicnic izzivni le pri 6,3 % oci. Pri bolnikih z RP je bila ohranjenost odgovora cepnic, draženih z vecjim številom dražljajev, za 25 % višja kot pri standardnem nacinu draženja (p = 0,005). Povezanosti med odgovori SF ERG ter izvidi vidne ostrine in vidnega polja nismo dokazali (- 0,5 < r < 0,5; p > 0,05).
ZAKLJUCKI: Na podlagi dobljenih rezultatov smo potrdili prvi dve hipotezi. Z uporabo višje svetilnosti dražljaja so bili odgovori SF ERG pri zdravih prostovoljcih in pri bolnikih z RP višji v primerjavi z odgovori, dobljenimi z nižjo svetilnostjo dražljaja. Pri enem izmed dveh nakljucno izbranih bolnikov je bilo možno izzvati prej neizziven odgovor. Zato je uporaba visoke svetilnosti dražljaja pri snemanju SF ERG primernejša za vrednotenje delovanja prizadete mrežnice kot svetilnost, ki so jo v našem laboratoriju uporabljali doslej. Z vecjim številom ponovitev dražljaja smo odgovor cepnic izzvali pri vec bolnikih z RP kot pri standardnem nacinu draženja. Nov nacin draženja je tako boljši za elektrofiziološko oceno delovanja cepnic. Tretje hipoteze nismo dokazali, saj med objektivno (SF ERG) in psihofizicnimi preiskavami (merjenje vidne ostrine in vidnega polja) v naši skupini bolnikov ni bilo povezanosti.
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[Abstract / English version]
ELEKTROFIZIOLOŠKA OCENA DELOVANJA CEPNIC PRI BOLNIKIH S PIGMENTNO RETINOPATIJO
Author: Tomaž Friedrich, Helena Skacej
Mentor: prof. dr. Marko Hawlina
Co-mentor: viš. znans. sod. dr. Jelka Brecelj
BACKGROUND: Full-field electroretinography (ERG) is the fundamental electrophysiological examination test which evaluates the retina function. It is performed in compliance with the standard recording procedure. The latter is readily modified according to new research results in order to improve the clinical value of the investigation. Full-field ERG is important in dealing with patients having the most common retina dystrophy - the retinitis pigmentosa (RP). This disease is clinically and genetically a very diverse condition with characteristically progressive and generalized degeneration of rods, cones and consequently also other cells of the retina. Besides full-field ERG which is an objective examination, also various psychophysical investigations are used to recognize and monitor RP. The most important among them are the measurements of the visual acuity and the visual field.
AIM: The normative values for the full-field ERG with a new stimulator producing higher luminance stimuli (flashes) than the present stimulator had to be determined by this research. We wanted to check the effect of the high luminance to the patients with RP. To stimulate cones which are still preserved in the course of the disease we also introduced averaging the responses with higher number of stimuli, this being a novelty to the standard recording procedures. This was supposed to evaluate the cone function with RP patients more objectively. With these patients we also wanted to determine to what degree the full-field ERG responses are correlated with the visual acuity and the visual field.
HYPOTHESES: 1. Due to higher luminance stimuli higher full-field ERG responses were expected with RP patients as well as with the control group. 2. For RP patients more recordable cone responses were awaited due to averaging the responses with higher number of stimuli. 3. Full-filed ERG responses, visual acuity and visual field were anticipated to be correlated.
METHODS: 30 healthy volunteers (34,8 14,7 years) and 16 RP patients (32,4 16,3 years) of both sexes were involved in the examination. All healthy volunteers had visual acuity of 1,0 and a normal fundus. Their responses to the full-field ERG with high luminance stimuli were screened. HK-electrodes were used as active electrodes. The preparation of the examinees and the parameter settings, except for the averaging the cone responses with higher number of stimuli, were in compliance with the previous standard recording procedures. The patients who participated in the examination had rod-cone RP, measurable visual acuity and visual field. The size of the latter was determined by the kinetic perimeter and its sensitivity with the static perimeter. The full-field ERG was screened as well. The Kolmogorov-Smirnov test was used to determine the distribution of the data. The Wilcoxon signed ranks test was applied with results of the healthy volunteers to determine the difference between higher and lower luminance. The same test was used for the patient results to prove the difference between averaging the cone responses with higher and those with lower number of stimuli. The correlations between the full-field ERG, the visual acuity and the visual field were determined with the Spearman correlation coefficient (r).
RESULTS: Healthy examinees had the full-field ERG amplitudes obtained with high luminance stimulus significantly higher compared to the lower luminance stimulus (p = 0,008) while the latencies did not differ statistically (p = 0,075). The variance coefficients (VC) of the higher luminance stimulus amplitudes were lower (p = 0,008) than the VC amplitudes of the lower luminance stimulus, while the latencies VC's between the higher and lower luminance stimulus, however, did not differ statistically (p = 0,767). The RP patients had the full-field ERG amplitudes higher with high luminance stimulus as well. This sort of stimulus on two randomly chosen patients with negative full-field ERG at lower luminance stimulus resulted also in detecting a positive response in one patient. Among all the full-field ERG responses the cone response obtained by the higher number of stimuli was preserved in 68,8 % of the patients' eyes while the rod response was detected only in 6,3 % of the patients' eyes. RP patients had 25 % more recordable cone responses using the higher number of stimuli compared to the standard one (p = 0,005). The correlations between the full-field ERG responses, visual acuity and visual field could not be proved (-0,5 < r < 0,5, p > 0,05).
CONCLUSIONS: Our results confirmed the first two hypotheses. Higher luminance stimulus resulted in higher full-field ERG responses for the healthy volunteers as well as for the patients. In one out of two patients a previously undetectable ERG response was now recorded. Therefore, the use of higher luminance stimulus for the full-field ERG is more suitable to evaluate the function of the degenerated retina. Averaging the cone responses with higher number of stimuli resulted in more RP patients having the cone response preserved compared to the standard recording procedure. Thus, the new stimulus provides a better evaluation of the electrophysiological function of cones. The correlation between the objective (full-field ERG) and the psychophysical examinations (visual acuity and visual field), however, could not be proved, so the third hypothesis was rejected.
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